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Maintenance & Technical (165)

FAA Revises and Clarifies the Cherokee Wing Spar Proposed Airworthiness Directive 2018-CE-049-AD

After receiving more than 100 comments and reviewing additional information, the FAA has removed some Cherokee models from AD 2018–CE–049–AD applicability list—but adds three others. 

On June 3, 2020, the FAA issued an update to an existing Notice of Proposed Rulemaking (NPRM) on Piper Cherokee PA-28 and PA-32 wing spar cracks. 

The update—a Supplemental NPRM (SNPRM)—is an amendment to the original NPRM.

There’s good news In the SNPRM for over 8,000 lower-powered fixed gear PA 28 Cherokee owners and some not-so-good news for Cherokee Six PA-32 260 and PA-32 300 owners. 

The FAA removed PA-28-140, -150, -160, -161 and -180 models from the applicability page of the AD; these airplanes are considered “low risk” and are exempt from the proposed AD. 

This note in the SNPRM explains why some PA-28 models were removed and why PA-32 models were added

“The FAA developed a more precise methodology for identifying risk. Flight loads of all similar models were compared to those of the PA-28R-201 (accident aircraft) as a baseline. Those aircraft models with calculated wing loads greater than or equal to 95 percent of baseline are considered at-risk and are included in the new effectivity.”

“This risk approach and the resulting change in applicability adds three airplane models (Models PA-32R-300, PA-32RT-300, and PA-32RT-300T).”

The new SNPRM restates the following from the original NPRM:

“This SNPRM would only apply when an airplane has either accumulated 5,000 or more hours TIS [Time in Service]; has had either main wing spar replaced with a serviceable main wing spar (more than zero hours TIS); or has missing and/or incomplete maintenance records.”

And add the following clarification:

“This SNPRM specifies that the owner/operator (pilot) may do the aircraft maintenance records review and the factored service hours calculation. Reviewing maintenance records is not considered a maintenance action and may be done by a pilot holding at least a private pilot certificate. This action must be recorded in the aircraft maintenance records to show compliance with that specific action required by the AD.”


Why is the SNPRM Issued?

Comments on the original NPRM from Piper aircraft, the National Transportation Safety Board (NTSB), and others, along with engineering and load revisions and feedback from inspections caused the FAA to write revisions into the proposal. 

The proposed AD will require affected owners to remove two bolts from the outermost end of the wing spar structure attached to the fuselage and conduct an inspection for cracks in that area utilizing a non-destructive method called eddy current inspections. 

Eddy Current Inspection Details

The SNPRM cites Piper Service Bulletin 1345 (dated Mar. 27, 2020) and titled, “Main Wing Spar Inspection,” as guidance for carrying out the eddy current inspection. 

Other changes from the original NPRM include expanding the qualifications for personnel qualified to conduct the eddy current inspections, increased the estimated labor hours to conduct an inspection, and increased the labor number of labor hours to replace a spar from 32 to 80. 

In addition, the SNPRM prevents the installation of a used spar in airplanes with failed spars. Only new spars may be installed.

After each eddy current inspection has been completed, a reporting form in the SNRPM—not the form in SB 1345—must be filled out and sent to the FAA and Piper within 24 hours if cracks are found, or within 10 days if no cracks are found. 

The FAA considers this SNRPM an interim action. If data from reports warrant changes, the FAA may take further rulemaking action.

As many readers already know, the original NPRM—issued December 18, 2028— requested that owners and other concerned individuals submit comments regarding the proposed actions in the NPRM. A total of 172 comments were filed before the comment period ended on February 4, 2019.

Piper Flyer readers can access the comments to the original NPRM at tinyurl.com/NPRMCherokeeWingSpar122118 . On the right side of the first page this is a window titled, “Enhanced Content.” Click on the “172” comments text to open the file.

This link also provides instructions on how to send comments on the new SNRPM. The new comment period ends July 20, 2020. 

Access the revised SNPRM at regulations.gov/document?D=FAA-2018-1046-0180

My article on the original NPRM “Piper PA-28 and PA-32 Wing Spar NPRM 2018-CE-049-AD” can be accessed here: https://tinyurl.com/EllsCherokeeWingSpar1 

That article includes information on 100-hour inspections and how to calculate factored service hours. 

Steve Ells has been an A&P/IA for 45 years. He is a commercial pilot with instrument and multi-engine ratings and loves utility and bush-style airplanes and operations. Ells an associate editor for AOPA Pilot. He owns Ells Aviation (EllsAviation.com) and lives in Templeton, California. Send questions and comments to



Newly issue SNPRM: regulations.gov/document?D=FAA-2018-1046-0180

Original NPRM: tinyurl.com/NPRMCherokeeWingSpar122118


A Roadmap for Effectively Responding to an NPRM

A Roadmap for Effectively Responding to an NPRM

PFA Contributing editor and A&P/IA Steve Ells, provides guidance for responding to an FAA Notice of Proposed Rulemaking (NPRM) with specific advice for the current SNRPM regarding the Cherokee wing spar concern. 

“A notice of proposed rulemaking (NPRM) is a public notice that is issued by law when an independent agency of the US government wishes to add, remove, or change a rule or regulation as part of the rulemaking process.”


The NPRM process is the norm for new rulemaking—issuing an airworthiness directive—unless the FAA decides that a safety issue is so time-critical that there’s no time for the NPRM process. In instances like this, the new rule, an airworthiness directive (AD) will go direct-to-final-rule. 

The Supplemental NPRM (SNPRM) issued on June 3 that relates to Piper PA 28 and PA 32 wing spar center section bolt hole eddy current inspections can be accessed at: https://www.federalregister.gov/documents/2020/06/03/2020-11343/airworthiness-directives-piper-aircraft-inc-airplanes.

That link will take you to the Federal Register page for this SNPRM. In the upper right corner, in a green box it says, “Submit a Formal Comment.” Below that is a link to take you to the 172 comments that were filed following the initial NPRM. 

In the discussion portion of the SNPRM, you’ll see how the FAA responded to comments and its rationale for those responses.

I recommend that you read through past comments. They will give a good idea of what makes an effective comment. 

There are guidelines that must be followed if you want your comment to be effective. They are in the Code of Federal Regulations (CFR) Section 11.43 and follow below:

(a) Your written comments must be in English and must contain the following:

(1) The docket number of the rulemaking document you are commenting on, clearly set out at the beginning of your comments.

(2) Your name and mailing address, and, if you wish, other contact information, such as a fax number, telephone number, or e-mail address.

(3) Your information, views, or arguments, following the instructions for participation in the rulemaking document on which you are commenting.

(b) You should also include all material relevant to any statement of fact or argument in your comments, to the extent that the material is available to you and reasonable for you to submit. Include a copy of the title page of the document. Whether or not you submit a copy of the material to which you refer, you should indicate specific places in the material that support your position.

The docket number and identifier for the Cherokee Wing Spar SNPRM are: Docket No. FAA 2018-1046. The Product Identifier is 2018-CE-049-AD.

Here are some rules of thumb for commenting:

Anger doesn’t work. 

Blaming the FAA doesn’t work.

Complaining about how much this is going to cost you doesn’t work.

Explaining that your PA-28/PA-32 was only flown to church on Sundays on severe clear no wind days; or any other reason you shouldn’t be bound by the AD doesn’t work.

What does work is a comment that contributes to a workable solution. In the case of SNPRM 2018-CE-049-AD, a comment that provides solution to the problem of cracks in the bolt holes in the wing spar center section.

After reading the SNPRM, which unlike the original NPRM prohibits the installation of a used spar center section, you might write a comment asking why a used spar center section can’t be used to replace one with existing cracks. Since the SNPRM makes no mention of a need for recurring inspections, you might ask why, if the used parts pass the eddy current inspection, they can’t be used. 

You might ask if the proposed AD will give any credit to owners who, after the first NPRM, (issued in December 2018) got their spars inspected and no cracks were found. Will that count as compliance with the AD, even if the AD is not issued until a later date? 

You might work with a Designated Engineering Representative (DER) to create what’s called an alternate method of compliance (AMOC) and submit that with the engineering data that supports it. For example, some who commented on the original NPRM said that the only end-all for these spar cracks is something like an external reinforcement with a spar strap or similar. 

Finally, if you don’t want to, or are unable to submit your comment electronically, the other methods of responding are listed below:

You may send comments, using the procedures found in 14 CFR 11.43 and 11.45, by any of the following methods:

Federal eRulemaking Portal: Go to https://www.regulations.gov. Follow the instructions for submitting comments.

Fax: 202-493-2251.

Mail: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590.

Hand Delivery: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

Steve Ells has been an A&P/IA for 45 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Templeton, California. Send questions and comments to


Checking Your Six: Comanche Stabilator Maintenance

Checking Your Six: Comanche Stabilator Maintenance


Piper’s long-running preference for stabilators began with the PA-24 Comanche. A&P/IA KRISTIN WINTER discusses the stabilator system and its most common problems, as well as what you can do to keep your tailfeathers airworthy.

The Piper PA-24 Comanche was the first Piper production aircraft to use an all-moving stabilator instead of the more common horizontal stabilizer and elevator combination. Piper obviously liked the result, as they used stabilators in the Aztec and in all the Cherokees and their derivatives.

Piper stabilators have proven to be fairly robust, with only a few issues that can easily be addressed with heads-up maintenance. In this piece, we will look at the known issues with Comanche and Twin Comanche stabilators.

Torque tube horn cracking
(AD 2012-17-06)

The stabilator system had been reasonably AD-free until 2012, when the FAA issued AD 2012-17-06, which addresses cracking in the torque tube horn that attaches the counterbalance arm to the torque tube, to which in turn the stabilator halves are attached.

The cracks propagate from the inside, as all three of the cracked horns in the photo show (See photo below).

The cracks progress from there to the outside, and eventually, a secondary crack will propagate on the aft side, as cracks in the front have now progressed to the point there is relative movement inside the horn. Once this happens, complete failure of the horn is likely but a few flight hours away.

A Tale of Two Pipers

A Tale of Two Pipers

Piper Aircraft Corporation’s expansion in the mid-1950s led to the opening of a second facility at Vero Beach, Florida. The differences between Piper aircraft designed and built in Lock Haven, Pennsylvania, and those born in Vero Beach, Florida, are numerous and important for owners, operators, and mechanics to understand.

While many Piper pilots are aware on some level that Piper used to make aircraft in Lock Haven, Pennsylvania, and now makes them in Vero Beach, Florida, fewer understand the significance of that bit of Piper history.

It is not too much to say that Piper Aircraft in Lock Haven is almost a different aircraft manufacturer than Piper Aircraft in Vero Beach. The change of location led to significant design differences that need to be understood.

A history lesson

To appreciate the differences between the two Pipers and their respective product lines, a bit of history is in order.

Most know that Piper got its start in Pennsylvania when William Piper, Sr. bought into Taylor Aircraft. Piper then bought Taylor out, and moved the company to Lock Haven, Pennsylvania, renaming it Piper Aircraft Corporation. This was back in the day of the Piper J-3 Cub, prior to World War II. (In “Piper Aircraft,” historian Roger Peperell notes that W.T. Piper bought out Gilbert Taylor in 1935, moved to Lock Haven and officially changed the company’s name in 1937.  —Ed.)

From the beginning, W.T. Piper sought to be the Henry Ford of aviation, attempting to make aviation affordable to the masses. With the Piper Cubs and their derivatives, Piper arguably achieved that goal.

After World War II, airplane development turned from tube and fabric truss construction to aluminum, semi-monocoque designs.

Piper’s first two all-metal aircraft were the Piper PA-23 Apache and the Piper PA-24 Comanche. These were both fine airplanes, but Piper’s lower-end line was still represented by the tube-and-fabric PA-20 Pacer and PA-22 Tri-Pacer. These models were competing against Cessna’s 170 and 172 series, which were more modern, all-metal aircraft. Piper needed a competitor to Cessna’s offerings, and they wanted to be able to produce it more cheaply. 

Piper faced a couple of limitations with building a less-expensive, all-metal competitor in Lock Haven. One limitation was that the Lock Haven plant had little room to expand. This made it difficult to add the facilities necessary to launch another line of aircraft.


Additionally, the Lock Haven facility was largely unionized, which meant that labor costs were high, making the goal of a relatively inexpensive competitor to the Cessna 172 more difficult to realize.

Vero Beach expansion

In the mid-1950s, Piper opened a second engineering, and then manufacturing, facility in Vero Beach, Florida.

Piper hired outside engineers, Fred Weick, Karl Bergey, John Thorp, and others to design a new aircraft that would be a modern replacement for the PA-22 Tri-Pacer. There was little cross-pollination with the engineering department in Lock Haven.

The result was the Piper PA-28 Cherokee, which was certified in 1960. One goal was for the Cherokee to be relatively cheap to manufacture. The Cherokee had fewer than half the number of parts of a PA-24 Comanche and fewer than half the rivets. The Cherokee was a design that had little in common with those coming out of Lock Haven.

Evolutionary design and the Cherokee

Once a manufacturer has made a clean-sheet design, it is natural to extend the basics of the design to make new products or to improve existing ones. Evolutionary design is standard in the industry. It is much cheaper to scale up or down an existing design rather than start from scratch. It saves engineering time and it makes an aircraft easier to certify.

The Cherokee series and its many derivatives are a classic example.

The original fixed-gear, four-place PA-28 Cherokee design begat models ranging in horsepower from 140 to 235. The PA-28 got a new wing in the 1970s, which was itself only a modification of the existing wing.

The new “Warrior” wing was a longer, tapered version of the original “Hershey Bar” wing, so called because of its rectangular shape and resemblance to the candy bar.

The new wing was of the same airfoil and had the same wing area. The change took the outer portion of the wing and tapered and lengthened it.

The fuselage was stretched, and a bigger engine installed to make the PA-32 Cherokee Six, but the general structure and the design details remained essentially the same.

Retractable landing gear was added to the PA-28-180 Cherokee 180 to make the PA-28R Cherokee Arrow. The same retractable landing gear system was added to the Cherokee Six to make the PA-32R Lance/Saratoga line.

The PA-32 Cherokee Six was modified to make the PA-34 Seneca by using two smaller engines on the wings in place of a single big one in the nose. A similar modification to the PA-28R-201 Arrow IV design resulted in the PA-44 Seminole.

Throughout all these changes, the structure remained fundamentally the same; the landing gear—fixed or retractable—remained the same; the control system remained essentially the same, and so on.

Lock Haven design characteristics

The same sort of design extension is true for Piper in Lock Haven and other manufacturers. However, Lock Haven did not stretch any of its designs as far as Vero Beach did with the original Cherokee.


There are certain hallmarks of a Lock Haven design. They always used the same basic design for how the wings and the fuselage met. They used the same hydraulic landing gear system in the Apaches, Aztecs, Navajos and Cheyenne series. They used bladder fuel tanks in most models, whereas Vero Beach did not.

Manufacturers’ similarities

Anyone familiar with the single-engine Cessnas will see the design similarities throughout. The same can be said of the twin-engine Cessnas (until you get into the Citation line of jets). Beechcraft got a lot of mileage out of the basic Bonanza design, which stretches back to the 1940s. And a Mooney is a Mooney is a Mooney.

When comparing different lines of aircraft from the same manufacturer, many of the design details and the way of doing things show their common origins (assuming they’re from the same engineering center).

The departures between the Lock Haven Pipers and the Vero Beach Pipers are fairly dramatic and it is worth keeping that distinction in mind. A Piper is not always the same animal, just because it is a Piper.

An instructor experienced in a PA-28R Arrow will know nothing about a PA-24 Comanche by dint of his/her Arrow experience alone. A mechanic that has worked on PA-28 Cherokees most of his career will be lost at sea when presented with his first PA-23 Aztec.

When dealing with Pipers, keep in mind that there were essentially two different Piper Aircraft companies.

Piper wing attachment designs

In the wake of the in-flight breakup of the Piper Arrow, operated by Embry-Riddle Aeronautical University, some Piper owners or prospective owners/pilots have expressed concern about the structural integrity of all Piper aircraft. In that accident, the left wing separated at the root.

The NTSB has just made a final determination as to the cause. It confirms that fatigue cracks propagated from the outboard bolt holes in the lower spar cap. Additional inspections of Embry-Riddle’s fleet of Arrows found another to be cracked in the same location. The FAA has proposed an Airworthiness Directive requiring eddy current NDT testing of the bolt holes looking for fatigue cracks.

The NTSB final report focuses on the numerous landing cycles that these aircraft experienced, which, in the case of the Embry-Riddle aircraft, was in excess of 30,000 landings, and the fact that these aircraft spent their operational life bouncing around at low altitudes. The NTSB report goes on to state that private-use aircraft are not subject to the same magnitude of repetitive stresses. (The final report was published by the NTSB on Sept. 3, 2019. For a link to this 30-page document, visit the PA-28 board under “Piper Models” at PiperFlyer.org/forum. —Ed.)

The Vero Beach Piper PA-28 Cherokee series and its derivatives, including the Arrow, all use the same structural design to attach the wings to the fuselage. The Cherokee uses a carry-through box structure that is built into the fuselage. The main spar of each wing has a stub portion that slides into the carry-through box, and then eight bolts go through the box and upper spar cap and 10 bolts go through the box and lower spar cap.

In contrast, the Lock Haven Piper design attaches the wings together in the center and then attaches the fuselage to the wings. The Lock Haven design has no carry-through structure built into the fuselage. Instead, the main spar of each wing extends out beyond the wing surface a distance approximately equal to half of the width of the fuselage. The main spar of each wing is attached to the other wing main spar with substantial splice plates on both the top and bottom, plus two channels on the front and back of the spar webs. The fuselage is then attached to the wing structure.

The engineering merits of the two types of structures can be debated. However, what is clear is that the failure mode that happened to the PA-28R-201 Arrow (and back in the 1980s to a PA-28-181 Archer) will not happen to the Lock Haven-designed aircraft such as the PA-23 Apache, PA-24 Comanche, PA-23-250 Aztec, PA-30 Twin Comanche, PA-31 Navajo, and the PA-42 Cheyennes.

From the PA-24 Comanche in-flight breakups which I have studied, it appears that the center sections on these aircraft do not fail and do not develop the same type of fatigue cracks as have occurred in the PA-28 series.

The in-flight breakups of which I am aware in the Lock Haven birds involved massive overloading usually caused by flying into a thunderstorm. Even then, it has not generally been the center section of the wings that broke, but rather an outboard section of the wing broke.

It should also be noted that the structure attaching the two halves of the wing together on the Lock Haven aircraft is easy to visually inspect. The Vero Beach Cherokee attachment system requires either sophisticated testing or removal of the wings.


We are all waiting for the other shoe to drop with the Cherokee wings in the form of an expected AD. It should be kept in mind that the aircraft which suffered the wing failures were all high-cycle aircraft. The first in the 1980s had thousands of hours of pipeline patrol flying; bumping along in summer turbulence day in and day out. The Embry-Riddle Arrow had over 6,000 hours of flight training use.

Keep in mind that the proposed AD does not require an inspection on an aircraft which has not had 100-hour inspections until something like 85,000 hours. The fact that the AD applies primarily to aircraft that have a long commercial use history suggests that it is not a factor for the average owner.

Kristin Winter has been an airport rat for almost four decades. She holds an ATP-SE/ME rating and is a CFIAIM, AGI, IGI. In addition, Winter is an A&P/IA. She has over 8,000 hours, of which about 1,000 are in the Twin Comanche and another 1,000 in the Navajo series. She owns and operates a 1969 C model Twinkie affectionately known as Maggie. She is a recognized authority on Piper Comanche aircraft. Currently she is serving as Director of Operations for a commuter airline in Southeastern Alaska. Send questions or comments to .

From Piper Flyer 1019

Piper PA-28 and PA-32  Wing Spar NPRM  2018-CE-049-AD

Piper PA-28 and PA-32 Wing Spar NPRM 2018-CE-049-AD

01/15/21 Editor's note: The final Airworthiness Directive has been issued and differs from this proposed version. 
A proposed AD requires an inspection of the lower wing spar cap on airframes with high-load or unknown usage history (as determined by a formula). STEVE ELLS shows you how to calculate your airplane’s “factored service history” and details the compliance steps and costs involved.

Dec. 21, 2018, the Federal Aviation Administration published a Notice of Proposed Rulemaking (NPRM), to define the proposed protocol for an inspection process to address the possibility of cracks in the lower wing spar cap of Piper PA-28 and PA-32 series airplanes.

After the crash of an Embry-Riddle Aeronautical University (ERAU) Piper PA-28R Arrow due to a wing separation on April 4, 2018, I researched and wrote a story about the accident, and looked back at the history of PA-28 and PA-32 wing cracks. The story appeared in the July 2018 issue oraf Piper Flyer. (See Resources for more information. —Ed.)

The importance of this proposed eddy current inspection is detailed in this sentence from the NPRM:

We are issuing this AD to detect and correct fatigue cracks in the lower main wing spar cap bolt holes. The unsafe condition, if not addressed, could result in the wing separating from the fuselage in flight.

The NPRM process

In my experience, the FAA often issues important NPRMs and Airworthiness Directives (ADs) just before a long weekend. This NPRM, 2018-CE-049-AD, was published Friday, Dec. 21, 2018. (See “Aviation Safety Alerts” on page Page 54 of this issue. —Ed.)

The NPRM proposal specifies that the AD will apply to the following Piper single-engine aircraft:

Model PA-28-140, PA-28-150, PA-28-151, PA-28-160, PA-28-161, PA-28-180,

PA-28-181, PA-28-235, PA-28R-180, PA-28R-200, PA-28R-201, PA-28R-201T, PA-28RT-201, PA-28RT-201T, PA-32-260, and PA-32-300 airplanes.

An NPRM is a preview of a proposed AD. The NPRM is an opportunity for owners, operators and other interested parties to respond to the proposal with comments, corrections and suggestions. 

The comments must have depth, breadth and be constructive. It’s important that the comments and corrections be based in experience and be factual. Comments that amount to nothing more than raging about cost or how the AD will decimate the fleet are of scant value. 

The comment period is 45 days from the date of issuance. Feb. 4, 2019, is the end of the comment period for 2018-CE-049-AD. 

“Factored service hours”

This proposed AD is unusual in that it requires owners and technicians to calculate “factored service hours.” The NPRM says:

This proposed AD would require calculating the factored service hours for each main wing spar to determine when an inspection is required, inspecting the lower main wing spar bolt holes for cracks, and replacing any cracked main wing spar.

The NPRM cites the discovery of a crack in the lower wing spar cap of a Piper PA-28R-201 as the reason for the proposal. It goes on to say:

An investigation revealed that repeated high-load operating conditions accelerated the fatigue crack growth in the lower main wing spar cap. In addition, because of the structural configuration of the wing assembly, the cracked area was inaccessible for a visual inspection. Model PA-28-140, PA-28-150, PA-28-151, PA-28-160, PA-28-161, PA-28-180, PA-28-181, PA-28-235, PA-28R-180, PA-28R-200, PA-28R-201T, PA-28RT-201, PA-28RT-201T, PA-32-260, and PA-32-300 airplanes have similar wing spar structures as the model PA-28R-201.

100-hour inspections as an indicator of high-load operations

Factored service hours are derived by researching the aircraft records to determine (1) the number of 100-hour inspections and (2) the total airframe hours, also called time in service (TIS). 

The factored service hours for each airframe are calculated by plugging the number of 100-hour inspections and TIS hours an airplane has accumulated into an equation. 

The rationale for using factored service hours (rather than total airframe time) is because the FAA believes that PA-28 and PA-32 airplanes used in flight schools, for-hire operations and other high-load environments such as low-altitude pipeline patrol, for example, are the airplanes that are subject to the heavy loading necessary for cracking to occur.

The NPRM says further:

Only an airplane with a main wing spar that has a factored service life of 5,000 hours, has had either main wing spar replaced with a serviceable main wing spar (more than zero hours TIS) or has airplane maintenance records that are missing or incomplete, must have the eddy current inspection.

How to determine factored service hours

The following is a summary of the formula for determining an airplane’s factored service life, published in the NPRM.

Step 1: Review the maintenance records (logbooks) to determine: a) the number of 100-hour inspections and b) total hours on the airplane since new or since any new wing or new wing spar replacement. 

Note: If a used spar or wing has been installed; or if the aircraft’s maintenance records are unclear as to the number of hours on the airplane, the bolt hole eddy current inspection must be done since it is impossible in those cases to determine how long the wing has been in service.

Step 2: Calculate the factored service hours for each main wing spar using the following formula: (N x 100) + [T-(N x 100)]/17 = Factored Service Hours, where N is the number of 100-hour inspections and T is the total hours TIS of the airplane. 

Thereafter, after each annual inspection and 100-hour TIS inspection, recalculate the factored service hours for each main wing spar until the main wing spar has accumulated 5,000 or more factored service hours.

The same formula is used to determine the factored service hours for all PA-28 and PA-32 airplanes. It works for those that have had only 100-hour inspections, those that have had no 100-hour inspections and airplanes that had some (but not all) 100-hour inspections over the life of the airplane.

Factored service hour calculations

Now, let’s do a few. Remember N is the number of 100-hour inspections and T is the total hours TIS of the airplane.

Picking numbers out of the air, let’s say our sample airplane has been used exclusively as a trainer for a well-known flight school for 4,662 hours and has had 46 100-hour inspections. What are the factored service hours of this airplane?

The formula for factored service hours is given in the NPRM as (N x 100) + 

[T – (N x 100)]/ 17 

For this airplane, that’s (46 x 100) + [4,662 – (46 x 100)]/17 

Simplified, (4,600) + [4,662 – (4,600)]/17

And finally, 4,600 + 3.657, which means this airplane has 4,603.65 factored service hours.

The inspection isn’t due yet, but will be soon, once the airplane reaches 5,000 factored service hours.

What about a privately-owned Piper PA-28-180 Cherokee 180 with complete maintenance records that has never had a 100-hour inspection?

Here’s an example straight out of the NPRM for determining factored service hours for an airplane with no 100-hour inspections. 

The airplane maintenance records show that the airplane has a total of 12,100 hours TIS, and only annual inspections have been done. Both main wing spars are original factory-installed. In this case, N = 0 and T = 12,100. 

Use those values in the formula as follows: (0 x 100) + [12,100 - (0 x 100)]/17 = 711 factored service hours on each main wing spar.

Despite the high number of airframe hours, this airplane has relatively few factored service hours and thus won’t need the inspection for quite some time.

Then, there are airplanes that have been used by a flight school, yet are now privately-owned. Here’s an example for an airplane that has 5,500 hours TIS and 25 100-hour inspections.

Use the same formula: (25 x 100) + [5,500 – (25 x 100]/17 equals 2,676 factored service hours.

This airplane is a little more than halfway to needing the inspection.

Math whizzes will recognize that the factored service hours formula is written based on an engineering calculation that wing spars in airplanes used for hire are 17 times more likely to have a spar crack than those that haven’t been flown for hire. 

My friend Mike Busch remarked:

The idea is that factored service hours are the sum of “abusive hours” and one-seventeenth of “non-abusive hours,” where “abusive hours” are defined as those hours during which the airplane was engaged in operations requiring 100-hour inspections (i.e., ops that included carrying passengers for hire and/or giving flight instruction for hire).

The only gotcha is for airplanes that have incomplete or approximated airframe hours instead of actual airframe hours. For instance, if an aircraft maintenance record (logbook) was lost or if one of the continuous record logs is missing, that airplane must have the wing spar bolt hole eddy current inspection specified in Paragraph (h) (1) and (2) of the NPRM and the inspection protocol in Appendix 1 of the AD. 

Inspection timeline and ongoing inspection requirements

The AD, as proposed, will require each airplane affected to have its number of inspections and TIS hours recalculated using the formula in the AD at each annual or 100-hour inspection to determine if it has gotten to the 5,000-hour factored service time point. 

Airplanes that get to 5,000 factored service hours per the formula, or airplanes with unknown airframe or wing hours TIS must have the eddy current inspection done within the next 100 hours time in service or 60 days, whichever occurs later.

According to figures in the NPRM, the eddy current inspection should take 1.5 man-hours. 

Reporting inspection results

The AD will require a written report within 30 days following each inspection. Here’s how it’s explained:

Within 30 days after completing an inspection required in Paragraph (h) of this AD, using Appendix 2, “Inspection Results Form,” of this AD, report the inspection results to the FAA at the Atlanta ACO Branch. Submit the report to the FAA using the contact information found in Appendix 2 of this AD.

Interim action

We consider this proposed AD interim action. The inspection reports will provide us additional data for determining the cause of the cracking. After analyzing the data, we may take further rulemaking action.

Based on these calculations, affected airframes that have never been operated where 100-hour inspections were required, seem to have little to be concerned about.

Airframes that have a factored service life of 5,000 hours or more will need to find a facility that can do a bolt hole inspection in accordance with the guidelines in Appendix 1 of the AD. 

If cracks are found, the wing spar will need to be replaced. The AD estimates that that repair will take 32 work hours and estimates that, at a labor cost of $85/hour the total cost will be $2,720 in labor. The FAA projects the part cost at $5,540, for a total cost of $8,260. 

However, since many of affected airframes are approaching 60 years’ time in service, I suspect that there will be owners and operators that elect to get the bolt hole eddy current inspection done regardless of the number of factored service hours on the airframe. It’s the only way to make sure there are no cracks. 

Know your FAR/AIM and check with your mechanic before starting any work.

Steve Ells has been an A&P/IA for 45 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Templeton, California, with his wife Audrey. Send questions and comments to .




“PA-28 and PA-32 Wing Spar Cracks: What You Should Know”
by Steve Ells, July 2018


NPRM 2018-CE-049-AD
Federal Aviation Administration
Pre-Purchase Inspection: All It Should Be

Pre-Purchase Inspection: All It Should Be

11 tips to help you make a smart buying decision.

The most important rule in the sales game is “you make your money when you buy something, not when you sell it.” When it comes to buying an airplane, it’s about saving money in the long run. Saving money happens to be a big factor in the airplane-happiness formula.

As outlined in my previous article “Start with the Right Airplane,” in August 2018’s Piper Flyer, once a thorough search has identified a strong candidate airplane, it’s time to commit to a thorough inspection. What follows is a list of observations and guidelines to use before and during a pre-purchase inspection:

1. Have the inspection performed at a neutral facility by a trusted inspector who is interested in protecting you.

2. The first thing I would verify during a pre-purchase inspection is that the data plate and logbooks actually belong to the airplane. That may sound crazy, but considering the age of the fleet and the many reasons a less-than-honest person can benefit from changing the identity of a damaged or stolen airplane, these things happen. At Air Mod, we have seen this issue rear its ugly head three times in the past 15 years.

3. Have copies of the logbooks sent to the inspecting agency in advance. Be suspicious of missing logbooks, sketchy entries, or unusual periods of idle time when the aircraft was not flown. Missing items or gaps in the documentation could be an attempt to cover up damage history.

4. Establish a clear understanding with the seller regarding your expectations, and let them know what item(s) constitutes a dealbreaker. Be realistic; you are not buying a new airplane. If a non-dealbreaking item is found, be fair and objective when negotiating the cost of fixing it. Don’t be a nitpicker. Choose your battles as to what issues you may want to negotiate.

5. Confirm that the equipment list conforms to what is actually installed in the airplane. Most importantly, affirm that the installed equipment is approved for the candidate airplane and that the proper paperwork verifying approval for installation in that exact make and model of aircraft is contained in the aircraft’s records. It’s also very important to inspect the quality of the workmanship and the components used in the installation.

The process of acquiring paperwork after the fact for previously-installed-but-undocumented equipment can be expensive, and perhaps, impossible. I like to get the original equipment list from the manufacturer and compare it to what is currently installed in the airplane. Deviations can then be checked out to ensure the required documentation is in the aircraft or engine logbooks.

6. Don’t buy a corrosion bucket. Your money is in the airframe. Almost all 30-plus-year-old airframes, most of which were not primed with zinc chromate during manufacture, will have some corrosion. But corrosion can be remediated and controlled with modern technology and proper intervention techniques. (Wolter will cover corrosion issues in more detail in future articles. —Ed.)

In Piper airframes, we tend to find the most cabin corrosion hidden behind and below the floor carpets. Unfortunately, one must remove the often glued-in-place floor carpet as well as any foam or heavy cardboard substrate material in order to inspect the belly skins and structure for corrosion. Additionally, the lower glued-in-place side wall carpet must be peeled back in the corners to inspect the steel riveted-in-place reinforcement corner brackets and seat belt attachment fittings. 


One final cabin item to inspect requires removing the windshield post plastic trim and inspecting the lower steel attachment brackets. We often find these critical steel reinforcement components to be rusting with their aluminum attachment rivets corroding.


The rest of the airframe (wings, aft fuselage, tail assembly, etc.) is easily inspected by removing inspection panels and fairings.

7. Identifying undocumented damage requires a careful and experienced eye. A savvy technician will know where and how to spot repaired damage. Overset rivets or driven rivets replaced with blind rivets are cause for some investigation. 

Shiny or zinc chromated new components in older airframes are just some of the clues that can reveal a secret. Be curious about a 40-year-old retractable-gear airplane; many have had gear-up incidents somewhere in the past.

8. Don’t overlook an evaluation of the avionics equipment in the candidate airplane. Having a knowledgeable technician ground-check the radios and autopilot is a very good investment. The technician can confirm that all equipment is approved for installation in the specific make and model of aircraft and that all components are approved to work together. They can also verify that the installation was done well. Not all work is good work, as shown in the accompanying picture.


9. Carefully inspect any modifications that were installed after the aircraft was built. Look closely to assess the quality of workmanship and verify that approvals and appropriate paperwork are included in the logbooks.



10. Ruling out the presence of hail damage is one inspection that’s sometimes overlooked. The best way to check for hail damage is to turn off the lights in a closed hangar and put a bright single light source as close to the aircraft skin as possible; look for any waviness in the skin surface that will be visible in the very low angle of the light. It is surprisingly difficult to see slight unevenness in a metal surface in bright overhead light. Skilled use of body fillers can hide almost any dent.

11. Not all engines are created equal. Low-horsepower four-cylinder Lycoming engines of 180 hp or less are about as bulletproof as they come. These engines can be evaluated with the usual maintenance record check, compression test, borescope cylinder inspection and an oil filter inspection. 

High horsepower equals high heat, and high heat equals more stress on cylinders, rings and valves. Add turbocharging to the system and there are more items to check out. Complex engines require careful and knowledgeable management and inspection. I personally believe the most predictable and cost-effective plan is to buy a high-horsepower airplane with a run-out engine and start your relationship with your airplane with a fresh quality overhaul.

It’s important to point out that not all overhauls are alike. By FAA definition, an engine can be considered overhauled if it has been disassembled, cleaned, inspected and all the critical components are precision measured to ensure that they meet minimum tolerance. 

This means that worn, but still serviceable, parts can be put back in an engine that can then be logged as overhauled and legally signed off for return to airworthy service. 

If one critical component experiences as little as one-thousandth of an inch of additional wear, the engine is no longer airworthy. So, hours since overhaul can have a significant—and precarious—meaning. (For more on this subject, see “My Engine is 50 Hours from TBO” by Bill Ross. You can find the article in the September 2018 issue. —Ed.)

The most predictable way to make sure an overhauled engine makes it to TBO is to require that it be overhauled using new limits. That means that all the parts begin their new life fitting exactly to new engine specifications and have a margin for wear that will help to ensure performance longevity, and, most importantly, safety—all the way to TBO.

Two more engine issues that are important to consider are how active the engine has been and how many years it’s been since it was last overhauled. 

Be concerned about an engine that was overhauled 20 years ago or has been inactive for an extended period of time. An inactive engine tends to develop corrosion and arthritic components, decreasing the likelihood that the engine and supporting components will make it to TBO. These conditions will often lead to increased maintenance issues along the way.

Writing this article reminded me of a wise older gentleman (fortunately, it seems like every airport has one) who said something years ago that I think was probably true, but at the time seemed a little harsh. He told me, “The three biggest lies in aircraft shopping are: one, no damage history; two, no corrosion; and three, the engine temperature and manifold pressures have never gone above redline.” 

Considering the age of the fleet today, these three comments are likely true and worthy of your attention. Be a smart buyer. 

Until next time, fly safe!

Industrial designer and aviation enthusiast Dennis Wolter is well-known for giving countless seminars and contributing his expertise about all phases of aircraft renovation in various publications. Wolter founded Air Mod in 1973 in order to offer private aircraft owners the same professional, high-quality work then only offered to corporate jet operators. Send questions or comments to .

Q&A: PA-34 Leaky Door Seals & Bouncing Fuel Gauges, PA-28R Main Gear Sidebrace Studs

Q&A: PA-34 Leaky Door Seals & Bouncing Fuel Gauges, PA-28R Main Gear Sidebrace Studs

Q: Hi Steve,

Couple of questions for you. I own a 1975 Piper PA-34-200T Seneca II Turbo. I have air leaks through the pilot entrance door. We’ve put in a new seal and adjusted it, but it still leaks. We think if we replaced the windlace with a new, more supple one that it would take care of the problem. Can you tell me where I could purchase this product? 

I also have a fuel gauge problem on the right engine. It does not indicate accurately and will vary between full and empty and anywhere between. What would be the best way to repair this problem? I read in your October 2016 issue on the Seneca II that Michael has had problems with this also. (See Resources for a link to the story. —Ed.)

I live in Glenwood Springs, Colorado, and fly out of Glenwood Springs Municipal Airport (KGWS). The runway is 3,300 feet by 50 feet, at 5,916 feet msl. The Seneca II operates very well here. Love this PA-34; it performs everything
I ask of it.

I appreciate any advice you can give me.



A: Hi Darwin,

Glad you like your Seneca. I wish I had one. 

The two companies that sell a variety of door seals are Brown Aircraft in Jacksonville, Florida, and Aircraft Door Seals in Wisconsin. I don’t have enough experience with these companies to recommend one over the other, but I believe both will send you a sample of the seal they recommend for your airplane so you can take a look at it. (Aircraft Door Seals is a Piper Flyer supporter. —Ed.)

I do know that Dennis Wolter of Air Mod, who is now writing for Piper Flyer, sometimes has to “build up” the surface behind the seal to get the seal he wants. Wolter uses flat rubber sheets in different thicknesses. He and his staff trim and adjust to get the proper build up. That tells me that you can have a very good length of seal, but you may still have to spend time tuning the installation to get the sealing you want. 

As far as your bouncing fuel gauge, it can be a couple of things. 

It can be problems with the gauge itself. Remove the signal wire at the sender and, while watching the gauge, touch the signal wire to the body of the fuel sender assembly. If the gauge is good, the needle should move smoothly from empty to full. If there’s hesitation or nonlinear needle movement, it’s probably a malfunction in the gauge.

If that looks good, you can test the fuel level sender by flying until the fuel level is below half so you can look inside the tank to locate the sender float.

Remove the signal wire from the sender. Then, by reaching in through the filler, use a safe tool to move the float on the sender arm up and down while an ohmmeter is attached to the signal stud on the sender. The varying resistance seen on the meter should be smooth and linear as the float is moved. I’ve used a long, smooth wooden dowel to move the float.

Other than visually inspecting the signal wire for bare spots—which is impossible in some installations—if you can find no other explanation for the bouncy needle, replacing the wire is probably the best solution. 

One option if you determine it’s the sender is to order new senders from CiES. They are much better and more accurate than the original Piper senders, and are FAA approved for installation on your Seneca. The CiES fuel level senders rely on a magnetic connection between the float arm and the signal arm. This type of connection eliminates corrosion and wear problems in the senders and provides a very linear signal. CiES senders are compatible with a wide variety of gauges and engine monitors.

Happy flying,


Aircraft Door Seals, a PFA supporter, will send prospective customers a sample of the seal material best suited for their aircraft.

Q: Hi Steve, 

Every 500 hours, my 1971 PA-28R-200 Arrow requires a removal and inspection of the main sidebrace bracket assembly to comply with an AD. My time has come...and apparently, it’s a bit of a job to remove these brackets. 

My A&P mentioned that if the brackets are replaced by those from a PA-32, then they will not require inspection again. The part numbers he provided me are: Part No. 95643-06/-07/-08/-09. I’ve found some new, but they are over $2,000 each! Any assistance locating some reasonably-priced alternatives would be greatly appreciated.



A: Hi Pete,

Your mechanic is referring to AD 97-01-01 R1. The title is “Main Gear Sidebrace Stud.” It calls for removal and inspection of the sidebrace studs. 

The initial inspection does not require the purchase of anything.

I suggest you remove the sidebrace stud brackets. It’s an easy task in my PA-24 which is also affected by the same sidebrace stud inspection as your PA-28R. 

After you remove the sidebrace stud brackets, remove the stud from the brackets and get your mechanic to find a shop near where you live that can do the fluorescent penetrant inspection or the magnaflux inspections called for in the AD. I believe all aircraft engine shops have the tooling to perform the magnaflux inspections. 

If you don’t find any cracks, reinstall the stud in the brackets and reinstall the brackets in the aircraft. Fly for another 500 hours and repeat. When I did the inspection on my PA-24, there were no cracks in either of my studs. 

The AD provides two ways to comply if cracks are found in either of your sidebrace studs. 

First, since the original-sized stud is no longer available, owners have the option of installing a larger stud in the original bracket after installing a new bushing and machining the larger stud to work with the original bracket and new bushing. 

Piper Flyer Association member Jason Williams added this on the PiperFlyer.org forum: “You can buy the new 5/8-inch stud (Piper Part No. 78717-02) and bushing (Piper Part No. 67026-12), along with the washers, roll pin and nut for around $700. A good machine shop should be able to ream and chamfer your bracket to accept the new parts.”

Thanks, Jason, your help is appreciated.

The second option is to buy new brackets, studs and bushings, and install these parts. 

As far as buying less expensive parts, that’s not as easy as it once was. Piper now sells its parts through Aviall, a national parts house. 

You may find the parts you need through an internet search or used from a salvage yard (see Resources for more information on how to locate parts and parts suppliers —Ed.) but they will have to be inspected in accordance with the AD prior to installation.

Let me know what the inspection turned up.

Happy flying,


AD 97-01-01 R1 calls for removal and inspection of the sidebrace studs for Piper PA-24, PA-28R, PA-30, PA-32R, PA-34 and PA-39 series airplanes.

Know your FAR/AIM and check with your mechanic before starting any work.

Steve Ells has been an A&P/IA for 44 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Templeton, California, with his wife Audrey. Send questions and comments to .



Aircraft Door Seals – PFA supporter
Brown Aircraft 


CiES Inc. – PFA supporter


Piper Flyer Yellow Pages
Piper Flyer parts locating request form (must be logged in)




“Life with a Seneca II” by Michael Leighton
Piper Flyer, October 2016
AD 97-01-01 R1, “Main Gear Sidebrace Stud”
Piper Flyer forum (must be logged in)
Engine Mounts Explained

Engine Mounts Explained

The engine mount represents a crucial link between your engine and airframe, and it should be treated as a mission-critical accessory. STEVE ELLS visited Loree Air, an FAA-certified repair station, for insight into the engine mount repair process.

I have found no evidence that my engine mount—that web of steel tubes that supports the engine and nosegear on my 1960 Piper PA-24 Comanche airframe—had ever been overhauled or recertified.

It seems a bit hard to believe. After all, it’s been bolted onto my airplane for 57 years. You’d think one mechanic or owner along the way would question whether the mount had suffered the ravages of time or had any issues. But like I said, when I started digging in the logs, I found no maintenance record entry that showed me it had ever received specific attention.

I recently discovered a cracked tube, and when I scrubbed it with a wire brush, I found a gaping hole—the tube had rusted through from the inside. I removed the welded steel mount in order to send it in for repair and recertification. 

As it turned out, the tube with the rusted spot was only one of seven tubes that had to be replaced. I had no idea the mount was in such bad shape!

What engine mounts are made of

SAE grade 4130 steel, also known as chrome-moly, is a through-hardened chromium-molybdenum steel alloy that is used in the light airplane industry where light, strong tubing is needed. It’s strong for its weight, easy to work, easy to weld and provides a good cost-to-strength ratio. 

Chrome-moly steel is available from aviation parts suppliers such as PFA supporters Acorn Welding, Aircraft Spruce and Airparts Inc. Wicks Aircraft also supplies this tubing. (Another PFA supporter, Wilco Inc., carries SAE 4130 in sheets. —Ed.)

The seven tubes that were replaced on my engine mount consisted of one 1/2-inch diameter tube, two 5/8-inch diameter tubes and four 3/4-inch diameter tubes. 

Chrome-moly tubing is purchased by specifying the outside diameter (OD) in 1/16-inch steps and the wall thickness. The wall thickness of the 5/8-inch OD tubes in my engine mount is 0.035 inch, which is close to the thickness of a credit card. The wall thickness of the 1/2-inch OD tubes is 0.049 inch, which is approximately the thickness of a CD. 

The 1/2-inch and 5/8-inch tubes sell for $4.35 per foot at Aircraft Spruce; the 3/4-inch tube is $3.35 per foot. 

I needed 4 feet of 5/8-inch tube and 68 inches of 3/4-inch tube to repair my mount before it could be recertified as airworthy. The materials cost was less than $50 at retail prices. 

A chrome-moly steel mount is a sweet piece of engineering. My refurbished engine mount (as delivered to me) weighs 15 pounds, 11 ounces; yet it is strong enough to support the Comanche’s Lycoming O-360 engine (258 pounds), a Hartzell two-bladed propeller (51 pounds) and support and endure the shocks suffered by my retractable nosegear.

The refurbished engine mount of the author’s 1960 PA-24 Comanche weighs 15 pounds, 11 ounces. It is strong enough to support a 258-pound Lycoming O-360 engine and a 51-pound Hartzell two-bladed propeller, and will also endure the shocks suffered by the retractable nosegear.
Removing and sending the mount out for repairs

After I found the hole in the lower right tube, I removed the engine and nose landing gear assembly. Removing parts, like the demolition phase of a room remodel, always goes quickly. In this case, I knew I needed to label and sort the parts and engine accessories because it was going to be almost two months before I was going to be reinstalling the engine and nosegear. 

One trick I’ve used for years when removing an engine or other assembly is to take photos of everything before picking up the wrenches. When I first heard of this photo trick, shops were using Polaroid cameras. Today, a cell phone and/or tablet is more than sufficient. 

One of the decisions that I pored over was where to send the mount for repair and recertification. I wanted an FAA-certified repair station that had the capabilities to repair and recertify my mount. My favorite internet search engine turned up four options. They were, in alphabetical order: Acorn Welding Ltd., Aero Fabricators (a division of Wag-Aero), Aerospace Welding Minneapolis and Loree Air Inc. and I have no doubt that there are others. 

I also searched for a used, serviceable mount. I found one on the East Coast and negotiated what I thought was a good price—but after learning that it would take more than $500 to ship it to me on the West Coast, the deal fell through.

Obviously, the cost of shipping a mount, as well as how to ship a mount, must be considered. Companies told me that the most common method is to bolt the mount to a piece of stout plywood, then either build a wooden or cardboard box around it for shipping by UPS or FedEx; or to bolt the mount to a pallet and ship it as truck freight. Since the repair facility has no control over handling after it leaves their possession, it’s critical to create a shipping container that protects the mount during shipping. 

PFA supporter Aero Fabricators quoted me $1,400, which included changing up to 10 tubes, and told me the turnaround time was two to three weeks. Aerospace Welding quoted a price of more than $2,500. 

Another PFA supporter, Acorn Welding, was unable to estimate their cost over the phone, but Paul Gyrko, head of sales, took the time to answer my questions and explain the full process when I called for information. 

Steve Loree Jr. at Loree Air told me that the cost to inspect, repair, normalize, paint and certify my mount would be $1,700 if it only required cleaning, inspecting, repainting and certification; and a maximum of $2,100 if work was needed. Loree also warned me the company had a five-week backlog. 

Given that Loree Air was only 278 road miles away from my home base—while the other three were all over 1,800 road miles away—and that I had good reports from friends that had used them, I decided to use the five-week window for other tasks and took my mount to Loree.

After another PA-24 owner offered to fly me up to Placerville to drop off the mount, I packed my sad old mount in the back of my buddy’s Comanche and flew it up to the Placerville, California airport (KPVF) where I left it with Nicole, who runs the office. 

Ready for pickup

Steve Jr. called on a Tuesday in late June to tell me that after cleaning and sandblasting all the paint off my mount, a thorough inspection revealed some surface damage to the exterior of a couple of tubes; bends in two tubes; and more tubes that showed evidence of internal rust. 

I asked him if it was OK if I drove to the shop once my mount was finished; I wanted to hang around and ask a lot of questions about mount damage and repairs. I figured this was an opportunity to pick up some hints and tips that a mechanic in the field could use to determine if a welded steel tube engine mount or landing gear support structure was airworthy. He said that would be fine.

Five weeks later I got the call; the repaired mount was ready. 

I arrived at Loree Air at 10:30 Monday morning. I met the entire staff: Steve Sr., Steve Jr. and Nicole (who is married to Steve Jr.). I was also sniffed up and down by Layla, the small four-legged office assistant and guard dog.


 Left to Right, Top to Bottom: Steve Sr.; Steve Jr.; Nicole; Layla (the hairy one).

Steve Sr. attained his welding certification at the San Diego shipyards and went to Sacramento City College for his A&P education at the suggestion of his flight instructor. He gained a wide range of reciprocating engine skills at the Sacramento Sky Ranch before spending 15 years working at the Sacramento Citation Center and at Aircraft Conversion Technology in Lincoln, California, with owner Bill Piper. 

Seeing the need for a certified aircraft welding shop in California and wishing to steer his own path, Steve Sr. opened Loree Air in 1992 in a small shop in the Swansboro Country neighborhood in the foothills east of Sacramento, near Placerville.

In 2011, Steve Jr. joined his father in the business. They decided that since the shop needed to grow in order to support two families, it was time to expand. To do so, Steve Jr. said, “I think we need a website,” but Steve Sr. wondered if it was necessary. Word-of-mouth advertising had been effective and the company had all the work it could handle. But Steve Sr. yielded, and today you can visit Loree Air online at LoreeAir.com. 

After consistent growth—thanks to the website—the Steves decided to move the company to a small warehouse and shop in Diamond Springs, another community near Placerville. 

With the help of many friends and family members, they planned and built a shop to fit the company’s needs. 

There had to be a large sandblast booth to clean mounts. There had to be a paint booth. There had to be an area for grinding and smoothing metal. The shop needed an area where mounts were put into jigs for alignment and buildup. A screened area was required for welding. A separate office and customer reception area were part of the plan as well.

There are also two lofts for storing parts and ready-to-ship mounts and nose strut welded tube support structures. 

While I had to take my mount to Loree Air to get in line due to the five-week backlog, the company does stock repaired and certified mounts for some popular aircraft. 

Problem areas

The Steves spent some time describing why my engine mount rusted out and passed on tips for determining if a welded steel engine mount is airworthy.

According to Steve Sr., “Piper mounts were not corrosion-proofed in the 1960s and early ‘70s.” He is referring to a practice of coating the inside of welded steel tube assemblies with a corrosion inhibitor. 

In the early days of aviation, linseed oil was used to inhibit corrosion. When I asked what else works, he replied that either LPS 2 or 3 heavy-duty lubricant works well and is readily available. 

The other Piper mount problem was the build sequence, which left small gaps at each firewall fitting around the bolt bushing boss. The gaps are small, but can allow moisture to get to the inside of the tubes. Loree has developed a build process that seals the mounts. 

Steve Sr. also pointed out that many Piper PA-28 Cherokee engine mount assemblies allow moisture to get into the tubes at the four engine support reinforcements, where the rubber vibration isolators—often called Lord mounts—are installed, because the two halves of the reinforcements are not sealed. This is also addressed when Loree repairs a PA-28 engine mount. 

Inspection tips and tricks

I asked the Steves for tips to help field mechanics determine if the welded steel mounts they inspect are airworthy. They said one test is to use an automatic center punch to put a small dent in the end of a tube that is believed to be unaffected by internal corrosion and compare that to the dent when the punch is used on the part of the tube that is suspected to be corroded. Usually this means comparing the dent at the highest part of the tube near a weld cluster to a dent in the lowest part of the tube. 

Any difference in the depths of the two dents is clear evidence the lower end of the tube has been weakened by internal corrosion.

Dents are repaired during the Loree Air rework. According to Steve Loree, the circular slot around the bolt hole is how moisture—a cornerstone of the rust process—enters the tubing in the mount. Loree seals this slot during rework.

While at the Loree shop, I also saw tubes that were dented during installation and removal by sloppy tool handling, and tubes that had been scratched or scored by abrasion.

Since these tubes are so thin, what may at first appear to be negligible damage usually needs attention. “Our standard for repair is 10 percent of the tube thickness,” said Loree.

One thing Loree was adamant about is avoiding the use of plastic tie-wraps (i.e., zip ties) to secure anything to a welded steel mount. He has seen it again and again: plastic tie-wraps will wear a welded steel mount tube faster than a pilot heads to a restroom after a cross-country flight. It takes longer to install properly-sized Adel clamps, but they are the only clamping device Loree wants used on an engine mount. 

You and your mount

I was surprised to hear Steve Sr. say that in all his years repairing mounts he had seen very few engine mounts pass through his shop that needed no repairs. 

I was also surprised when my mount needed seven tubes replaced. 

Then I saw pictures of the inside of those tubes. They were all rusted to one degree or another. I believe good fortune was smiling on me when I found the crack that lead me to remove my mount to send it for repair. 

Rust was clearly present in seven of the author’s engine mount tubes. They were all replaced by Loree Air.

Based on what I learned and saw, I recommend that owners send their engine mounts to a certified mount repair shop to get inspected, repaired-as-necessary and recertified whenever their engine is removed for overhaul.

Steve Ells has been an A&P/IA for 44 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Templeton, California, with his wife Audrey. Send questions and comments to .


Acorn Welding

Aircraft Spruce and Specialty Co.

Airparts Inc.


Wicks Aircraft and Motorsports


Wilco Inc.

Acorn Welding Ltd.

Aero Fabricators
(a division of Wag-Aero)

Aerospace Welding Minneapolis

Loree Air Inc.

ITW Pro Brands

Preparing for a Renovation

Preparing for a Renovation


Identifying squawks and properly sequencing your Piper refurbishment projects can save you time, money and aggravation.

So you’re now the proud, new owner of a not-so-new airplane that you plan to own for a long time. Fortunately, you properly vetted this new-to-you airplane during a thorough pre-purchase inspection, and you’re looking forward to renovating it into your ideal machine. The most important component in successfully making your dream a reality is to develop a cost-efficient, thorough and well-planned renovation plan.

A very important first step is to get to know the airplane before moving forward with major renovations and upgrades. I highly recommend that an owner fly their newly acquired airplane for at least a year and get it through its first annual inspection. 

Even though a thorough pre-purchase inspection was done, be prepared for that first annual to possibly cost 10 percent of what you paid for the airplane. I’ve made this statement several times in the past during seminar presentations. Looking out at the audience, it’s interesting to observe the various reactions this comment generates in the expressions of those seated in front of me. Surprised or shocked looks indicate non-owners considering their first purchase. Nods of agreement come from seasoned airplane owners.

Why such an expensive first annual? Good question. It’s only natural for an owner who is planning to upgrade to a different airplane in the foreseeable future to defer maintenance issues that can be safely put off, passing the expense on to the next owner. 

As you fly the airplane for that first year, it’s a good idea to keep a notebook with you. While comfortably cruising along, make detailed notes about things you would like to change to improve your experience in the airplane, as well as maintenance issues that may only be apparent in flight. 

Note such items as cabin and instrument lighting, storage, passenger restraint issues, potential heating and ventilation improvements, seating comfort, instrument panel layout, etc. Over a year or so, you will be surprised to realize the number of details that you will want to include in your wish list that you weren’t at all aware of when you purchased the airplane. 

I also think it’s a good idea to keep a small camera in the airplane and use it to capture images of paint jobs or interiors that you see and like; this can help you make better choices later. Designing a custom interior or paint job involves a lot of thought and planning. Having images of what you like will help the professionals you partner with to design and execute a project that will meet or exceed your expectations with no details overlooked.

The following is a list of sequenced projects that will lead to a thorough and high-quality renovation. We will cover all of these topics in greater detail in future articles to help you and your inspector find issues that could have been missed in earlier inspections.


• Engine

– Overhaul or upgrade

– More horsepower, turbocharger conversion

– Converting carbureted to fuel-injected

• Improved baffles

• Alternator and starter upgrades

• Cowling modifications

• Replace old hoses

Speed-enhancing full nosegear fairing.



• Shoulder harnesses and belts

– Four-point vs. three-point


Four-point BAS inertia-reel harness.

– Inertia-reel vs. fixed harness

– Airbag belts

– Adding harnesses to center and aft seats

• Fire extinguisher

• Ballistic parachute

• Lighting

– LED beacons, nav and landing lights

• Modern flameproofed interior materials

• De-icing systems

• Backup instrument systems



• How much digital automation is right for me?

• Keeping some existing analog equipment?

• What brand of equipment is the best investment?

• Instrument panel options

– Dealing with plastic panel overlays

– Converting to all-metal panels

– Panel lighting options

– Old circuit breakers and switches

– Autopilot options

– Onboard weather detection


Custom instrument panel in a Piper Lance. 


• Gap seals

• Fixed and retractable landing gear   

• Clean-up mods

• Auxiliary fuel systems



• Windshield conversions

– One-piece vs. two-piece

• Thicker windows vs. standard thickness

• Tint options

• UV-reflective glass vs. standard

• Windows with opening vents



• Stripping vs. topcoat over existing paint

• Stripping options

– Alkaline vs. acid-based strippers

– Media blasting

– Ice crystal blasting

• Getting the right design

– Design it yourself

– Use a professional

• Finishing products best for aluminum airplanes

• Best finishes for fabric-covered airplanes


A Saratoga in the painting process.



• Aging airplane issues

– Leaking windows

– Corroded structural components

– Glue-covered and corroded inner cabin skins

• Approved seat modifications

– Taller seat backs

– Adding headrests to older seats

– Installing late-model seats in older airplanes

• Side panel and armrest design

– Factory configuration

– Modified or upgraded

• Storage options

• Insulation options

• Ventilation upgrades

• Lighting upgrades

• Materials

– All-leather seats and side panels

– Fabric and vinyl seats and side panels

– All-vinyl seats and side panels

– Headliners

– Carpet

– Flameproofed materials and Federal regulations

• How much interior installation can an owner legally do?

– Using kits

– Partnering with a local upholstery shop

• Typical warranty coverages for various projects


New interior in an Archer, with ergonomic seats and custom side panels.

This list is not all-inclusive or cast in stone, but these various projects are loosely sequenced based on issues that could compromise previously completed work. For instance, old fuel cells that require replacement every 15 to 20 years should definitely be taken care of before a new paint job is done. The same is true for most window installations. If either of these two items are showing signs of aging and are likely to fail before that paint is in need of being done again, do the glass or fuel cells first.

All of this probably sounds complicated, expensive and time-consuming, and it is. Most owners stage these projects when it’s most convenient in their schedules or when they’ve recovered from the expense and downtime of the previous project. Additionally, many of these tasks can be partially or fully completed by an owner, saving money and giving one a real sense of accomplishment. In subsequent articles, I will describe some tricks we’ve discovered over the years that will help the do-it-yourselfers.

These kinds of restoration ventures don’t happen overnight. Air Mod was involved in completing five AOPA sweepstakes airplanes between 1994 and 2013. The time it took to complete most of these spinner-to-tailcone total renovations was close to a year, and they were not undertaken by only one shop. The “Better Than New 172” project in 1994 was a bit of a timing exception. The investment of long work days and seven-day work weeks resulted in a complete renovation that included avionics, autopilot, custom instrument panel, windows, custom leather interior with highly modified side panels, four-point inertia-reel harnesses, super soundproofing and a custom paint job, all of which took about five months to finish, as opposed to the more common 10 to 12 months.

Be prepared to face the realities of the time it takes to transform your airplane into your dream machine. Until next time, fly safe!

Industrial designer and aviation enthusiast Dennis Wolter is well-known for giving countless seminars and contributing his expertise about all phases of aircraft renovation in various publications. Wolter founded Air Mod in 1973 in order to offer private aircraft owners the same professional, high-quality work then only offered to corporate jet operators. Send questions or comments to .

Comanche Stabilator Horn Inspection

Comanche Stabilator Horn Inspection

Piper PA-24 Comanches are subject to AD 2012-17-06, which requires inspection of the stabilator horn for cracks and corrosion. A&P/IA Steve Ells describes proper procedures for removal, inspection and reinstallation.

June 22, 2011, the FAA issued a Notice of Proposed Rulemaking (NPRM) that asked all concerned parties to comment on a proposed AD. The proposed AD would mandate an initial inspection of the stabilator horn assembly for cracks and corrosion on Piper PA-24, PA-24-250 and PA-24-260 Comanche single-engine airplanes. After the initial inspection, replacement or continued inspection would be required.

Since I am the happy owner of a 1960 PA-24, I followed this closely.

Comanche owners contributed many comments seeking to relieve and/or clarify the requirements of the original NPRM. Some suggested that the FAA make changes due to mitigating factors such as the wall thickness of the stabilator torque tube, nut-tightening torque values on the bolts that secure the horn to the torque tube and other concerns.

The NPRM was written because cracks had been found in several stabilator horns. The submitted comments were well-regarded by the FAA and raised valid points. After changes and updates, AD 2012-17-06 was issued Aug. 22, 2012. 

The review of the initial proposed rule, the comments, names of the commenters and the FAA’s responses to the commenters can be read in full on the FAA’s website. (A link to the page is in Resources. —Ed.)

AD 2012-17-06 and Piper Service Bulletin No. 1189 (April 29, 2010)

A little over five years ago, in early January 2013, I pulled the stabilator horn assembly on my Comanche and drove it over to Johnston Aircraft in Tulare, California, for the initial inspection. In my opinion, Johnston ranks right up there with three other Comanche shops in the country. 

I watched as Charles Gazarek at Johnston showed me how to remove the aluminum horn and then perform the inspection steps mandated by the AD. No cracks were found in the horn. 

This horn is an aluminum part that connects the stabilator torque tube to the cables that control aircraft pitch through the horn assembly. The horn assembly consists of the horn, a tube (Piper Part No. 22880-00) and a balance weight (Part No. 23175-00). The torque tube is secured to the aft bulkhead of the fuselage by four bolts that hold bearing block assemblies in place. The torque tube rotates in two large sealed bearings. The stabilators slide over the torque tube and are secured by two bolts on each side. 

The left bearing block and torque tube. 

The AD calls for an initial inspection, and then repetitive inspections every five years or 500 hours TIS, whichever comes sooner. The horn must be removed from the aircraft and inspected for cracks by dye penetrant or other means. 

The timeline for complying with the initial inspection requirement of the AD varies based on the age and origin of the horn. Refer to the AD for details, but the short version is that if a horn has not been inspected since the AD was published in 2012, it is likely due for an initial inspection.

The repetitive inspection can be terminated by installation of what’s known as the Aussie horn, which is a stronger replacement horn that was developed in Australia and is approved for installation by a STC. (For more on this alternative, see the sidebar on Page 28. —Ed.)

Pull those tailfeathers

Removing my left and right stabilators was easy. (The author, Steve Ells, is an A&P/IA. Repair work such as this must be performed or supervised by an authorized mechanic. —Ed.) I removed the two close-tolerance (AN175) corrosion-resistant bolts on each side that I installed to comply with a previous AD (AD 74-13-03 R1) and slid both stabilators off the torque tube. They slid right off since I had cleaned and polished the tubes and applied a light coat of LPS-2 prior to reinstallation five years ago.

The stabilator control cables attach to the torque tube assembly at the forward end of the tube at the balance weight. I cut the safety wire and slacked both cables, then removed the bolt that connected the cable terminations. 

Then I removed the two bolts that secured the balance weight on the tube, and slid the weight off.

Next, I removed the upper and lower tailcone fairings and the tail navigation light bulb socket after disconnecting the trim tab actuating arm assembly (Part No. 20828-00) and electrical wiring to get access to remove the torque tube.

After removing the two bolts of the yoke assembly that supported the trim tab drum assembly to the blocks that hold the torque tube bearings and lowering the yoke and drum assemblies, I removed the four bolts securing the bearing blocks and pulled the torque tube assembly out from the aft bulkhead. 

The bearings, bearing blocks, torque tube and horn have been removed from the aft bulkhead. 
Preparing for inspection

After removing the assembly from the airframe, I slid the two bearings and blocks off each end of the torque tube, then slid the aluminum horn off the tube for inspection.


These two photos are from Piper Service Bulletin No. 1189, Fig. 1. The black lines on the aluminum horn assembly indicate the areas to be inspected.


None of this was difficult. Because the tube had been previously cleaned, the bearings slid off easily. I checked the bearings for ease of rotation. They were smooth and free. The left and right bearings had been replaced in the past. Newer bearings have a white Teflon seal; original bearings have a red seal. 

After I heated the horn for a few minutes with my electric heat gun (an electric hair dryer will work), it slid off the tube.

I stripped off the “rattle-can” primer paint I had applied after the last inspection with off-the-shelf paint stripper. 

Piper Service Bulletin No. 1189 shows two horns that had cracked. In each case, the cracks were through the bolt holes either at the front or aft side of the horn.

I looked closely at the horn with a very bright light but couldn’t see any evidence of cracking. The next step was the dye penetrant inspection.

It took me just over three man-hours to get to this point. 

Dye pen(etrant)

The AD requires an inspection in accordance with the instructions given in Piper Service Bulletin No. 1189. According to the bulletin, cracks start at the inner surface, so there’s no need to remove exterior paint from the horn to complete the inspection. Simply clean the inside of the horn with isopropyl alcohol prior to performing the dye penetrant inspection.

A dye pen inspection consists of cleaning the surface, then applying a coating of the penetrant, which is a very viscous red liquid. Leave the dye in place for a few minutes so it can penetrate any surface cracks, then clean the part completely. The dye pen kit I used consisted of a can of spray-on cleaner, a can of spray-on dye and a can of spray-on developer. 

As you can see by the photo, I sprayed a generous coat of dye onto my horn. After a few minutes, I sprayed the provided cleaner on a clean rag and wiped off all the dye. 

After drying the horn, I sprayed on an even coating of the developer. The dye is ruby red, while the developer looks a lot like spray-on talcum powder. The developer coated the surfaces of the horn.

I was looking to see if I saw red lines in the white developer which would indicate cracks. Luckily, there was no evidence of cracking. So, I cleaned the horn and started reassembling the torque tube assembly.

The stabilator horn, liberally coated with dye. 

I again smoothed and cleaned the outer surfaces of the torque tube with a Scotch-Brite™ pad before applying a light coating of LPS-2. Then I slid the horn into position. 

The most critical reassembly task was applying the correct torque to the two bolts that hold the horn in position on the torque tube.

I then slid the left and right bearings and blocks onto the torque tube. There was no need to remove the part called the stabilator torque collar. This collar, which appears black in the photos on bottom of Page 30, is part of the stabilator travel adjustment system. 

The service manual calls for a dimension of 8.620 inches between the left and right bearing block. If that dimension is not attained, shims are installed to achieve it. Mine checked OK.

The stabilator horn assembly is mounted to the rear bulkhead with four 5/16-inch diameter bolts, two in each bearing block. The nuts are torqued to the standard torque (there’s a standard torque table in the service manual) for 5/16-inch bolts loaded in tension. That torque value is 100 to 140 inch-pounds.

Once the bearing block bolts were torqued, I moved the trim tab drum yoke into position and installed and safetied those bolts. Then I slid the left and right stabilators onto the torque tube and secured and torqued those bolts. Checking stabilator balance and travel

After the tail was reassembled but before I reconnected the pitch system control cables, I followed the procedure in Chapter 4 of the Piper PA-24 Service Manual to check the stabilator balance. First, I leveled my Comanche. A stabilator is in balance when it can be moved to any position throughout full travel and not move once placed in any position. Mine was balanced.

I then connected the control cables and positioned and tensioned the up and down cables to provide the mandated control wheel travel and the stabilator travel. 

I rechecked my procedures and steps, then when satisfied that all was as specified, I reinstalled the tailcone fairings after reconnecting the power and ground wires to the tail navigation lights. 

In all, the removal, inspection, reinstallation and rigging and travel checks took very close to a full day of work, or 8 man-hours. (For reference, AD 2012-07-16 estimates the entire inspection process, including removal and replacement, takes 12 man-hours. —Ed.)

After completion of the steps in the AD, I entered a maintenance record (logbook) entry that is signed and reads similar to this: “October 29, 2018: Airframe total time 3,255. Complied with AD 2012-17-06, dated Oct. 22, 2012 (g) (2) (i) and (5) and Piper Service Bulletin 1189 Instructions 1 through 6. No cracks found. AD is next due October 29, 2023 and 3,755 aircraft total time.”

Now my stabilator horn is airworthy for another 500 hours or five years. 

No cracks were seen after applying the white talcum-like developer. 
Not too tight; it’s a shear load

Paragraph 5 in the “Inspection/Replacement” section of AD 2012-17-06 mandates that the bolts that go through the horn and torque tube be torqued to 120 to 145 inch-pounds or 10 to 14.5 foot-pounds. It doesn’t sound like much, especially for bolts that may at first seem to hold the tail together!

There are two reasons for what seems to be a low torque value. The first reason is because overtorqueing the nuts has been determined to be the cause of the cracking. There’s no need to apply a hefty torque since the nuts don’t need to do any more than prevent the bolts from falling out. 

The second reason is because of the bolt loading. This bolt-nut combination is loaded in shear, not tension. The bolts transfer the up and down motion of the horn/tube and balance weight into rotary motion of the torque tube. 

To apply the correct amount of torque, the friction drag of the nut’s locking element first must be determined. Common aircraft-quality self-locking nuts “lock” in position due to either a fiber insert in one end of the nut or by a slight out-of-round section of a steel locknut. 

How many inch-pounds of turning force does it take to overcome that locking component? The easiest way to determine the friction drag is with a deflecting-beam torque wrench. The following is the equation as published in the AD: 

The stated torque value of 120–145 in.-lbs. includes friction drag from the nut’s locking element, which is assumed to be 60 in.-lbs. The installation torque can be adjusted according to the actual, measured friction drag. For example, if the friction-drag torque is measured to be 40 in.-lbs. (20 in.-lbs. less than the assumed value of 60 in.-lbs.), then the installation torque will be adjusted to be 100–125 in.-lbs. of torque.

The steps are to first determine the friction drag of the nut’s locking element in inch-pounds and then adjust as necessary to get the final torque.

A reliable torque wrench is crucial for reinstallation of bolts on the stabilator horn.

Know your FAR/AIM and check with your mechanic before starting any work.

Steve Ells has been an A&P/IA for 44 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Templeton, California, with his wife Audrey. Send questions and comments to .


Johnston Aircraft Service Inc.
AD 2012-17-06
Federal Aviation Administration
Piper Flyer’s Magazine Extras 
PDF available at PiperFlyer.org/forum
Off to a Good Start: Planning for your First Annual

Off to a Good Start: Planning for your First Annual

Evaluate and maintain a new-to-you aircraft using all of the tools available today.

So, it’s been a year since the pre-purchase/annual inspection was completed and you have been the owner of this new-to-you airplane. As the months passed, every flight revealed more details about the condition and usefulness of your new flying partner. 

You probably encountered a few issues that required immediate attention and many others that became line items on your to-do/wish list. (In last month’s Piper Flyer (November 2018), Dennis Wolter outlined best practices for preparing to tackle a renovation. —Ed.)

With this list and your maintenance technician’s familiarity with your new airplane, the arrival of annual inspection time presents the perfect opportunity to sit down with your mechanic and put together a schedule for the renovation of your airplane.

In the list that you put together when flying the airplane during previous months, it’s important to include maintenance and performance issues that need to be discussed before starting that all-important first annual. 

I definitely believe that you should read all applicable Airworthiness Directives and Service Bulletins and confirm that important issues are well-understood and properly completed. Just because an AD is signed off in the logbook doesn’t mean that it was done properly or even that it was done at all. A couple of times a year at Air Mod, we find evidence that a signed-off AD was, in fact, never taken care of. 

The point here is that between a thorough pre-purchase and the first annual, all issues are checked and verified, and your airplane should be off to a good start toward working its way to being a “good as new” machine.

From a safety standpoint, the condition of your airplane’s engine is of major importance. You should take advantage of every technical process available for evaluation and maintenance in this area. 

Back in the day, inspecting an oil filter for contaminates such as metal particles and performing a simple compression check were the two major engine evaluation processes that a technician used in determining the health of the piston engine.

Compared to my early days in this industry, we now have at our disposal far more inspection and diagnostic tools that make it possible to operate our engines longer with greater confidence. 

Determining engine health

A compression check is done to determine the health of the upper or power section of the engine where combustion takes place. Combustion exposes pistons, rings, cylinder walls, valves and valve guides to a lot of heat and combustion byproducts. 

The time-tested compression check involves a technician using compressed air and air pressure gauges to determine if the cylinder and all of its parts are doing the job of sealing in the combustion gases in such a way as to efficiently produce the desired pressure of pushing the piston down to turn the crankshaft and rotate the propeller. Any leaking of these high-temperature gases past the valves or the piston and ring assemblies will cause heat buildup, a decrease in engine performance and increased wear on these critical components. 

As good as the compression check was and is, it falls short of presenting all the information needed to fully evaluate the condition of the combustion components of a piston engine.

Beam-me-up-Scotty to 2018. Today, we have three diagnostic tools that bring engine condition tracking to a whole new level. 

Tool No. 1: Borescopes

The first implement I refer to here is the affordable, state-of-the art borescope. What’s that, you might ask? It is a 1/2-inch diameter, 18-inch-long fiber-optic tube that can be placed in an engine cylinder through a spark plug hole. It will present a high-resolution color-correct image on a bright screen that allows a technician to evaluate the condition of the cylinder walls, piston crown, valves, etc. 

Borescope being placed in an engine cylinder.

Often, an engine that has good compression will have stress marks on the cylinder walls or discoloration on valves that can only be seen with a borescope. These anomalies can indicate a potential for future problems. The borescope allows a technician to address an issue before it becomes a failure. Also, most borescopes have a built-in digital camera, making it easy to email a picture of a problem to the customer. So much for the good old days!

Here is a great example of the value of this technology. I called a good friend, Adrian Eichhorn, who has done quite a bit of research into the use of this technology, to help identify cylinder components that are in the early stages of failure. He sent me a photograph of an exhaust valve that presented an uneven color pattern, indicating that the valve was becoming too hot in one area and not sealing at that point on the edge of the valve. 

Uneven color pattern on an exhaust valve indicates a possible problem. 

If not corrected, the valve will eventually begin to deform and lead to serious and expensive valve failure. Eichhorn, in partnership with AOPA, came up with a chart showing various color patterns that indicate different types of potential valve failures. These charts have been distributed and used in the field with very positive results. Smart! (A link to the PDF is available under Resources at the end of this column. —Ed.)

These borescopes are miracle investigative tools that allow technicians to see into inaccessible areas in various parts of the engine and airframe. I have a customer who recently used one to find a badly-corroded elevator component that was close to failure.

Tool No. 2: Oil analysis

Another important area to be evaluated is the bottom end of the engine—the crankshaft, connecting rods, oil pump, camshaft, etc. Back in the good old days, about the only diagnostic tool a technician had to help establish the condition of these components and their bearings was to hold a magnet in the oil as it drained out of the engine and look for magnetic or ferrous metal particles sticking to it. A technician could also cut open the full-flow oil filter, if the engine was equipped with one, and look for metal fragments in the filter. 

Magnetic fragments mean a steel component is experiencing high wear; nonmagnetic fragments mean a nonmagnetic component such as a bushing is wearing, or something is rubbing the aluminum crankcase. Fragments don’t always provide enough information to accurately diagnose a potential problem. Big pieces of metal indicate serious pre-failure issues.

The second engine diagnostic tool I’m going to discuss is oil analysis. It can vastly improve a mechanic’s ability to assess an engine’s health. 

Here’s how it works: as the technician is draining old oil out of the engine, a small cup is filled with an oil sample that is sent to a laboratory for analysis. After testing, the lab returns a report to the technician that indicates the percentage of metal residue found in the oil, measured in parts per million and listed by type of metal. Iron can indicate wear on the oil pump gears; silver can indicate wear on a plain bearing such as connecting rod or crankshaft main bearings; bronze can indicate wear on valve guides, and so on. 

As the engine builds hours and additional oil samples are analyzed, a technician can track data and determine wear trends of the various internal engine components. If a high reading of a specific metal is noticed, the technician can use this information to identify a possible point of failure and initiate the appropriate maintenance action.

Tool No. 3: Engine monitors

The third 21st-century device that has revolutionized the monitoring of piston engine operation and maintenance is the digital engine monitor with data download capability. The complexity of these systems can range from basic exhaust gas and cylinder head temperature monitors to systems that replace existing round engine instruments with a full screen that has multiple additional read outs for voltage, percentage of horsepower, fuel remaining and even outside air temperature.

Digital engine monitor with data download capability.

These systems allow valuable information to be downloaded and analyzed by an owner, a technician or an online company, to track engine condition trends. Science fiction has become reality. We should take advantage of these contemporary tools to ensure the safe and efficient operation of an engine all the way to TBO. (See Resources for a list of PFA supporters. —Ed.)

Other items to evaluate


An annual inspection item that I believe is sometimes not carefully looked at is the age and condition of the fuel, oil and vacuum flex hoses. Many rubber flex hoses in service today have a service life of five years. Failure of an oil or fuel hose can definitely contribute to a bad day! 

I highly recommend replacement of timed-out hoses with hoses fabricated with cost-effective, safety-enhancing orange fire-resistant sleeves, which protect the hose and its often-flammable contents in the event of an electrical or engine fire. The photo shows a typical black hose with a service life of five years as well as a stainless steel fitting, fire-sleeved silicon rubber, extended service life, top-of-the-line hose.

Extended service life hose on top, typical black hose below. 

Engine accessories

Moving beyond the engine itself, it’s important to monitor the service life and condition of the engine accessories. A good pre-buy inspection should have clarified the times in service and inspection status of all the stuff that keeps the engine running. 

An owner needs to be aware of the status of these components in order to prevent as many surprises as possible.


Let’s focus now on a big item: magnetos. Most brands of magnetos require a 500-hour half-life inspection and a 1,000-hour overhaul or replacement. Experience has shown that scheduled maintenance and monitoring is very effective in increasing the reliability of these critical components. 

Vacuum pumps, propeller governors

We know that dry vacuum pumps driving traditional gyros have a higher failure rate after 500 hours of operation. Propeller governors are best overhauled at engine change. The failure of a prop governor can send engine-damaging metal through the engine’s lubrication system—that means big bucks to fix! The point here is to have a meeting with your maintenance tech and totally vet the status of all firewall-forward systems. 

Engine overhauls

OK, I’m walking on thin ice here. No discussion about piston airplane engines would be complete without talking about the often-debated subject of time between overhauls (TBO). It seems like experts are all over the map as to when a seemingly great-running engine should be overhauled. Opinions range from “TBO is cast in stone” to “TBO is an arbitrary, money-making number set by the engine manufacturer.” (See “Further Reading” in Resources for more on this topic and other topics discussed in this article. —Ed.)

Here’s an 18-year-long anecdotal study I was unintentionally exposed to during the time Air Mod was located next to one of the more active field overhaulers in the country. Located by their hangar were two dumpsters. One contained rejected ferrous metal engine parts (crankshafts, connecting rods, gears, cams, etc.). The other contained rejected nonferrous aluminum parts (crankcases, cylinder heads, etc.). Most of the engines going through their facility were overhauled at or near TBO. 

Based on the quantity of rejected parts that got hauled off to the recycling facility, I tend to think that the manufacturers base TBO numbers on experiences they’ve had tracking these engines for almost a century. Just remember, you can’t write the check on the way down!

If it’s time for you to schedule that engine overhaul, tune in next time as we look at the options and process involved overhauling your trusted engine. Until then, fly safe.

Industrial designer and aviation enthusiast Dennis Wolter is well-known for giving countless seminars and contributing his expertise about all phases of aircraft renovation in various publications. Wolter founded Air Mod in 1973 in order to offer private aircraft owners the same professional, high-quality work then only offered to corporate jet operators. Send questions or comments to .



Electronics International
Insight Instrument Corp.
J.P. Instruments Inc.


“Anatomy of a Valve Failure”
PiperFlyer.org/forum under “Magazine Extras”


“My engine is 50 hours from TBO….” by Bill Ross
Piper Flyer, September 2018
“A Step-by-Step Guide to Overhauls” by Jacqueline Shipe
Piper Flyer, February 2018
“Is Your Engine Worn Out?” by Steve Ells
Piper Flyer, October 2017
“Dissecting a Dry Air Pump” by Jacqueline Shipe 
Piper Flyer, June 2017
“I Found This in my Oil” by Jacqueline Shipe 
Piper Flyer, May 2017
Q&A: Adding Toe Brakes to a Cherokee, Hand Controls for Wheelchair Aviators

Q&A: Adding Toe Brakes to a Cherokee, Hand Controls for Wheelchair Aviators

Q: Hi Steve,

I just bought a 1968 PA-28-180 Cherokee 180 B. So far, it’s been wonderful, but there’s one thing that I haven’t yet gotten used to. I trained in a newer Cherokee and it had toe brakes. My airplane just has a brake handle that I pull on to apply both main brakes at the same time. 

How can this be a good idea? Every airplane I flew in my training had toe brakes and whenever I wanted to turn sharply, I used the brake to sharpen my turn. I can’t do that in my “new” Cherokee and I am hoping you can point out how I can install toe brakes in my airplane. 


A: When I looked in the PA-28 and PA-28R Parts Catalog (Piper Part No. 753-582) for the PA-28-180, the way I read it, toe brakes were available on the left side on the PA-28-180 from Serial No. 28-1 up through 28-7305611.

The serial number range for your airplane, the Cherokee 180 B, includes serial numbers from No. 28-671 through 28-1760.

Toe brakes were an option from the factory. All Cherokees were equipped with hand brakes, but only the ones that were ordered with toe brakes also got the factory-installed toe brakes. 

There is no STC to install toe brakes on Cherokees. I have heard of owners who went to an aircraft salvage yard for the entire toe brake package—pedals, crossbar supports, links, firewall reinforcements, master cylinders and other parts that were available—and had these parts installed. Since all the parts are listed in the parts manual for the Cherokee 180, this is certainly doable. 

Some mechanics will say this change is a minor alteration for two reasons. First, Piper already approved the installation of the toe brake system at the factory and all the parts are Piper-produced. Second, it is not listed in the list of major alterations in Appendix A of Part 43 of the regulations. Minor alterations require only a logbook entry for a return to service.

Despite those facts, these days most shops will seek FAA approval in the form of a field approval sign off on a Form 337 (Major Repair and Alteration). This is despite the fact it’s becoming increasingly difficult to get a maintenance inspector at a local Flight Standards District Office (FSDO) to sign off a 337.

For what it’s worth, I did see a set of Cherokee toe brake pedals on eBay today. It lacked the master cylinders and the necessary firewall reinforcements, so you’d have to source those parts elsewhere.

My 1960 Piper PA-24 Comanche is the first airplane I’ve ever owned that does not have toe brakes. At first, I was skeptical too. 

I soon learned that I didn’t miss the toe brakes at all. Part of the reason is that I used to lock up and flat-spot tires when I had toe brakes. That got expensive. Yes, I had to learn to live with the turning radius of my Comanche, but now that I know about it, the larger turning radius hasn’t been a headache. 

Many owners with the handbrake controls, myself included, strongly suggest that you live with your hand-actuated brake system for a few months before you make your final decision. It’s a good system.

Happy flying,


A Piper handbrake, like this one installed in Steve’s PA-24 Comanche, is simple to operate. The brake system applies equal braking pressure to the main wheels. Just pull the handle to slow down.

Q: Hi Steve,

I expect my mechanic can answer this, but I haven’t asked him yet. I have a Piper PA-28 Cherokee that I’ve owned for years. This airplane has been a central part of our family trips and vacations. 

My son was severely hurt last year in a motocross accident and has lost the use of his legs. He gets around fine in his wheelchair and has expressed an interest in flying. I have heard something about wheelchair pilots, but don’t have any details. 

Is there a way to equip my Cherokee so that my son can take flying lessons?

Flying Dad

A: Hi Dad,

I’m sorry to hear about your son’s accident.

Yes, theoretically there’s a way to equip your Cherokee with controls that will enable your son to safely fly your airplane. But unless you can find a used set of hand controls to install in your airplane, it’s going to be tough.

Unfortunately, the two companies that developed hand controls for disabled pilots and had them approved through what’s called a Supplemental Type Certificate (STC) are no longer producing the hardware and paperwork for installation of the controls.

STC SA1741WE approves the installation of hand controls in PA-28-140, -150, -160, -180, -235 and PA-28R-180 and R-200 aircraft. This modification is sometimes known as the “Blackwood hand control” after the originator. The STC is presently owned by Mike Smith, but is not in production.

During my research, I spoke with Justin Meaders at International Wheelchair Aviators. Meaders is a pilot and uses a wheelchair. He was able to update me on the state of STCs for equipping Pipers for pilots who require hand controls to fly. 

Meaders told me he is working to get the FAA to recognize the Blackwood hand control for Pipers as a medical device that would not require an STC for installation.

Vision Air of Australia has Australian approval for a hand controls system for Cherokees, but it hasn’t been approved for use in the United States.

There is a similar STC for Cessna hand controls known as the Union control. The STC is in suspension now, but has been purchased by Linwood Nooe of Operation Prop in Brandon, Mississippi. 

I asked Nooe if he knew of a source for the hand controls. He told me that his nonprofit organization offers flights and flight training to men and women that can’t operate foot controls, and that people donate used controls to him from time to time. 

Nooe also invited anyone who needs hand controls to fly to come to his facility in Mississippi  for both introductory flights and flight training. (Nooe’s contact information is in Resources. —Ed.) 

You can view videos of hand-controlled flights using the Vision Air controls and Union control on the website of the United Kingdom-based nonprofit Freedom in the Air. (See link in Resources. —Ed.)

Best wishes on helping your son fly,


These diagrams, provided by Linwood Nooe, show the Union hand control.
It is similar to the Blackwood control used on Piper Cherokees. 

Know your FAR/AIM and check with your mechanic before starting any work.

Steve Ells has been an A&P/IA for 44 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Templeton, California, with his wife Audrey. Send questions and comments to .


Federal Aviation Administration

Federal Aviation Administraton

Able Flight

Freedom in the Air (flight videos)

International Wheelchair Aviators

Operation Prop (Linwood Nooe)

Vision Air

Rules For Owner-Performed Maintenance

Rules For Owner-Performed Maintenance

As an aircraft owner and pilot, you can legally perform some maintenance tasks, but you must adhere to strict guidelines when doing so. STEVE ELLS walks us through packing wheel bearings, while highlighting what’s important to stay legal.

As most readers of Piper Flyer know by now, all aircraft maintenance tasks must be overseen or performed by an appropriately-rated person. For maintenance tasks, this means an A&P mechanic—or a technician, as some like to be called these days—is frequently both performing and signing off on the work. This mechanic must (by regulation) have up-to-date versions of the appropriate manuals, bulletins, tools and equipment necessary to complete the tasks. 

However, there are also a number of maintenance tasks that owners may legally perform. These are termed preventive maintenance (PM) tasks. There’s a long list of them in Appendix A of FAR 43. 

What is considered preventive maintenance?

Appendix A is titled, “Major Alterations, Major Repairs and Preventive Maintenance.” Paragraph (c) lists preventive maintenance tasks. Type “Appendix A of Part 43” into your favorite search engine (or find the link in Resources on Page 33. —Ed.).

There is a surprisingly long list of tasks allowed. For instance, owners are permitted to remove and replace batteries, replace bulbs, reflectors and lenses of position and landing lights, and replace prefabricated fuel lines. 

They can also remove and replace panel-mounted communications and navigations receivers and update databases in panel-mounted avionics such as GPS navigators. 

Great news, right? It is, especially if a pilot has the time and a place to do these tasks. The potential for saving money exists, but much more important is the satisfaction to be gleaned from learning how to take care of your own airplane. (For further reading, see the sidebar on Page 32. —Ed.)

Are you permitted to perform preventive maintenance tasks?

FAR 43.3 paragraph (g) says that “…the holder of a pilot certificate issued under Part 61 may perform PM on any aircraft owned and operated by that pilot which is not used under Part 121, 129 or 135 of this chapter.” 

So, according to this section, if the owner and pilot is not using his airplane for hire, whether on a scheduled service, an on-demand service or as a foreign carrier operating for hire in the U.S., he/she can perform PM. 

But there’s a catch. It’s in 43.13. It’s titled “Performance Rules (General).”
43.13 Performance Rules (General)

The following three points—from paragraphs (a) and (b) of the performance rules—have been abbreviated to simplify the important points the maintenance performance rules for owners. 

1. Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer’s maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques and practices acceptable to the Administrator.

2. He [or she] shall use the tools, equipment, and test apparatus necessary to assure completion of the work in accordance with accepted industry practices. 

3. Each person maintaining or altering, or performing preventive maintenance, shall do that work in such a manner and use materials of such a quality, that the condition of the aircraft, airframe, engine, propeller, or appliance worked on will be at least equal to its original or properly altered condition (with regard to aerodynamic function, structural strength, resistance to vibration and deterioration, and other qualities affecting airworthiness).

In other words, if you’re going to do PM, you must follow the procedures in the manuals. It’s as simple as that. 

It’s important at the outset to understand that airplane maintenance, while seeming to be like automobile or other gas engine maintenance in that it must be done right, is different in a very important way. In airplane maintenance, there is a published protocol for every operation, even the tightening of a nut or bolt. 

Another peculiar-to-aircraft trait is this: the strength versus weight equation must always be kept at the forefront of every operation and decision. In other words, if you believe that more is better, whether it be the size of a bolt or the amount of torque, you’re going to do more harm than good. 

Gathering the manuals and bulletins to meet the requirements of the FARs is much easier and less expensive than it used to be. The secret is the internet. Manufacturers have come to realize that making their manuals and bulletins available at no cost or consolidating a double-shelf full of manuals onto a CD is a sound idea, simply because access to manuals makes it much easier for maintenance shops (especially smaller shops) to access the precise methods and techniques the manufacturer has developed for maintaining its product. 

So, step one for owners that want to start working on their airplanes is to have or have access to manuals, and either have the tools or be able to manufacture the tools required to properly perform each maintenance task. 

Let’s look at an example of why manuals are important.

Greasing wheel bearings: a “simple” preventive maintenance task

Greasing the wheel bearings on an airplane may seem simple. At its most basic, it can be described in the following steps: First, jack up the airplane or axle enough to get the tire off the ground, then remove the axle nut and pull the wheel/tire assembly off the axle. Next, remove each bearing, clean it and the bearing race, inspect for damage or corrosion, replace if necessary, pack with grease and reinstall. Finally, reinstall the tire/wheel assembly, tighten the axle nut and lower the tire to the ground. 

Not so fast. There’s more to it. In fact, there’s quite a bit more.

To remove the tire/wheel assembly (TWA), the brake assembly must be partially disassembled. This disassembly requires the removal of two or four bolts to release what’s called the brake back plate(s). The TWA can be removed only after the back plate(s) have been removed.

Assuming the airplane has been jacked up far enough to lift the TWA, a large cotter pin must be removed prior to removing the axle nut. Then, the TWA can be pulled from the axle.

There is an inner and an outer bearing. Does a Piper parts book refer to these bearings? No. Piper parts books don’t show an exploded view of the wheels. Piper parts manuals only provide the Cleveland part number for the wheels on its single-engine airplanes.

That means you also need a Cleveland manual for dimensions, wear limits and bolt torque specs when greasing the wheel bearings on your Piper single. 

Here’s another thing to know that is hard to find in any manual: Bearings and races are matched pairs. Don’t take the bearing assembly you removed from the race on the valve stem side of the TWA and install it in the race in the non-valve stem side of the TWA.

What grease to use?

The 2009 Piper Lance service manual suggests the use of Aeroshell 22 grease and Mobil EP 2 grease (also marketed at Mobilux™ EP 2), which is a lithium-based grease. 

Cleveland, the manufacturer of brakes and wheels used on Piper singles, suggests the use of Mobil SHC™ 100 grease. 

Bearing removal, cleaning and greasing

After the TWA has been removed, the bearings are removed. This usually requires the removal of a snap ring, a washer, a felt grease seal and another washer. 

Bearings are then cleaned with Stoddard solvent, applied by either an air-powered solvent sprayer or a brush. Air can be used to blow the grease out, but never spin a bearing by directing compressed air perpendicular to the rollers. 

Directing a stream of air across—not between—the rollers in roller bearings is dangerous because the bearing cage is designed only to maintain the spacing between the rollers. It’s not strong enough to contain the rollers when they rotate at a high rate of speed; in other words, directing air across when bearings can result in fast-moving projectiles.

After the bearing is clean and dry, look for corrosion and/or pitting. If found, replace the bearing and matching race.

Bearings are repacked by putting a gob of clean grease in the palm of either hand and forcing the grease up into the bearing. Press the bearing down into the grease until the bearing comes into contact with your palm. Repeat this procedure until grease appears at the top of the bearing cage.

You can also buy a bearing packer and use it to pack the bearing. Look up “wheel bearing packing tool” on your favorite search engine. YouTube also has wheel bearing packing videos. (See Resources for an additional article that discusses wheel bearing service. —Ed.)

The last step is to look at the grease seals. For decades, Cleveland, the manufacturer of most GA wheels and brakes, has used felt pads to seal against sand and fine dirt. These seals are inexpensive and work well. 

Recently, Cleveland has replaced the felt pads with molded rubber grease seals. These may be used in place of the felt seals.

Putting it all back together

The newly-greased bearings are reinstalled in the side of the wheel which they came from. Slide the TWA onto the axle. If it doesn’t slide all the way on, you’ve got the large steel washers on each side of the felt seal in wrong. Swap the washers around until the TWA slides all the way onto the axle.

Thread the axle nut onto the axle. 

How tight should it be? I couldn’t find definitive information on how tight the axle nut should be. Field experience suggests to tighten the nut up well to seat the bearings, then loosen it until you can feel a slight movement of the wheel in and out on the axle, then snug it back down until the TWA spins without resistance and no in-out movement is felt.

Now, to reassemble the brake. Two or four bolts were removed so the back plate could be removed to free the brake disc from the inner and outer brake pads. 

Whenever I have a TWA off the axle, I clean up the brake guide pins with a Scotch-Brite pad. I also clean the guide pin holes in the torque plate. These guide pins must slide in and out to allow the brake to self-adjust as the brake pads wear. 

The devil is in the details

The last step is often missed as it’s not in the Piper manual. It’s found in the Cleveland Wheels and Brakes Component Maintenance Manual, Appendix A titled, “Wear Limits and Torque Values.” This manual, and all of the Cleveland wheel and brake manuals, are available for free on the Cleveland website. Start by downloading the Technician’s Service Guide. (See link in Resources. —Ed.)

Piper parts books don’t have all of the information needed to service a tire and wheel assembly. The Technician’s Service Guide from Cleveland Wheels & Brakes can be an essential companion for owner-performed maintenance.
Oftentimes, similar-looking parts call for different torque values. It is crucial to use the correct value for your part. 

This critical step in reassembly is applying the proper torque to the two or four back plate tie bolts. Overtorqueing the bolts can deform the brake housing. 

The proper torque on almost every Piper single engine brake is 75 to 90 inch-pounds (6.25 to 8.5 foot-pounds). That ain’t much. It doesn’t need to be much since these bolts aren’t in a compression application. They are loaded in shear, and as long as these bolts are snugged down to the proper torque, that’s sufficient. 

Sign off your work

The good news is that owners can legally do a lot of work on their airplanes. However, as mentioned, there are catches. Catch No. 1 is that you must own or have access to the manuals. Catch No. 2 is that you must enter the work you performed in the aircraft records in a manner that’s acceptable to the Administrator. That’s FAA talk for the head of the agency. 

The requirements for these entries are listed in FAR 43.9. It says if you perform PM, you shall make an entry in the maintenance records containing the following information:

1. A description of the work performed.

2. The date the work was completed.

3. The name of the person performing the work.

4. If the work was performed satisfactorily, the name, certificate number and signature of the person performing the work. The signature constitutes an approval for return to service only for the work performed. 

(This is a summary of FAR 43.9. Please refer to Resources for a link to the complete text. —Ed.)

Notice that the regulations do not require the entry to include the aircraft total time or tach time, but it’s extremely helpful to include that information. 

An example1 of an entry for the work described above would read:

Month/day/year. “Greased left and right main landing gear wheels in accordance with information in the Piper (model number) service manual and the Cleveland Wheel and Brake Component Maintenance Manual, Appendix A, paragraph A3.”

Signed: Joe Pilot Cert # 1245654

The point of this article is to make sure owners understand the freedom and the limitations that are part of owner-performed PM. Go ahead and do it, but make sure you do it right; by the book. 

1For more about complete and detailed logbook entries, see “Deciphering Logbooks: Pre-purchase Maintenance Record Review” by Kristin Winter in the December 2017 issue. 

Know your FAR/AIM and check with your mechanic before starting any work.

Steve Ells has been an A&P/IA for 44 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Templeton, California, with his wife Audrey. Send questions and comments to .



Part 43.3, Part 43.9, Part 43.13, Appendix A to Part 43

Electronic Code of Federal Regulations

Technician’s Service Guide AWBTSG0001-1

Cleveland Wheels & Brakes– PFA supporter

Component Maintenance Manual AWBCMM0001-12

Cleveland Wheels & Brakes– PFA supporter
“Wheel Bearing Service: Why and How” by Jacqueline Shipe 
Piper Flyer, July 2016 



Engine Overhaul Fundamentals, Part One: Understanding the Process

Once you’ve made the big decision to overhaul your engine, you’ll still need to figure out where and how the overhaul will happen. In order to make the best choices for your engine and budget, you’ll need to understand the overhaul process. 
In the first of a four-part series, Dennis Wolter walks you through the basics of what happens in a typical overhaul.

My mentor flew Martin B-26 Marauders in World War II. He told me a story back in 1960 when I was just beginning to learn to fly that really resonated with me. When his bomber group first arrived in England, the base commander addressed the new flight crews at their first pre-mission briefing. 

The commander began that briefing with a very good piece of advice, stating, “Remember the seven Ps: proper prior planning prevents p--- poor performance.”

The key word in that statement is definitely planning! Planning starts with accessing information and choosing the best option. By now, most all of you folks can see that proper research and planning is a central theme of my articles.

Of the many stages involved in renovating an airplane, good research and planning is most important when you’re deciding how and where to have your engine overhauled.

Due to the complexity of engine overhauls, I will cover the total scope of the topic in four articles. In this first article, I will review the step-by-step procedure of overhauling an engine. 

An aircraft engine is complex; so is an engine overhaul. 

The second article will discuss overhaul options, including a local individual A&P overhaul; having a facility specializing in major field overhauls do the job; and having an overhaul or rebuild performed at the factory. 

The third article will cover support and installation details that need to be considered to ensure that your fresh engine has a good home. 

The fourth and final article will address upgrade options, such as converting to higher horsepower, turbocharging, propeller upgrades, etc.

Overhaul process: first steps 

In order to help break down all this information, let’s take a tour through a major overhaul facility. 

The first step of teardown and cleaning begins with an organized disassembly and layout of the components by type. The parts are then chemically degreased and cleaned in a hot solution of solvent. With the gross amount of oil, dirt and carbon removed, some of the parts are also detail cleaned with media blasting to get them thoroughly cleaned.

After disassembly, parts are thoroughly cleaned.

The technicians then put every component through an alignment and a precision dimensional check to ensure that no parts are bent, worn or damaged to a degree that they cannot be reconditioned and placed back in service. 

Reusable components are then either turned over to highly-skilled in-house technicians or shipped to an off-site facility where each piece is reconditioned to meet minimum service limits or new limits depending on the quality standards the customer has chosen.

Inspecting the components

Crankshaft, connecting rods, bearings 

The heart of a piston engine is the crankshaft, so let’s start there. The technician begins by placing the crankshaft in a fixture that supports the shaft at both ends. The probe of a precision dial indicator is positioned to press against various positions on the crankshaft. 

Precision measurement of the crankshaft.

As the crank is rotated in this fixture, the dial indicator will show little to no movement if the crankshaft is straight. If too much movement is seen on the dial indicator, the crankshaft must be replaced. 

If the crankshaft is not bent, it is put through a crack-finding process known as magnafluxing. It is mounted in a machine that runs a strong electric current through the full length of the steel crankshaft, causing the crank to become magnetized. A solution of solvent and iron filings is poured over the crankshaft.

The business end of a magnaflux machine that magnetizes steel parts. 

If there is a crack in the metal, the disturbed magnetism at the point of the crack will cause the magnetically-sensitive iron filings to align themselves along the crack and clearly show a visible irregularity. 

This magnaflux inspection process will be performed on all steel parts. A cracked component must not be put back in service. 

If the crank passes these inspections, it is potentially eligible to be reconditioned and reused.

Next, the technician will inspect the round surfaces that support the crank and the four or six connecting rods and bearings that are attached to the crankshaft. These journals, as they are called, must be perfectly round, smooth and machined to a very precise dimension. If any scoring or excessive wear is identified, these conditions must be corrected by re-machining and polishing. 

The connecting rods that attach the piston to the crankshaft are precisely measured for length and straightness. After passing that test, they are magnaflux tested for cracks. 

Finally, the bushing that serves as the bearing where the piston is attached to the connecting rod is inspected for condition and wear. If the bushing is out of tolerance, a new one will be required.

Camshaft, valve lifters, cam lobes, gears and bearings

Another high-wear area in the valve drive mechanism is where the camshaft and lifters open and close the valves. The camshaft and valve lifters are inspected using the same magnafluxing methods as used on the crankshaft. 

A magnetized camshaft being doused with iron particles to identify a crack. 

Both the cam lobes and lifter faces where the cam rubs the lifter are heat-treated and polished to a very smooth and hard finish when manufactured. These hard surfaces are very thin. 

Camshafts can be reconditioned. However, if a significant amount of this thin surface material is removed during the re-grinding process, the life expectancy of the reconditioned part is limited. 

I believe that re-grinding a camshaft lobe or mating surfaces of the valve lifters may not always be the best choice. Think seriously about installing new cams and lifters. 

In the back of the engine are several steel gears and bronze bearings that need to be magnafluxed and inspected for cracks, condition and wear.

Oil pump

Certainly, let’s not forget the oil pump. All three basic parts of this important component must be assessed. Personally, I would not reinstall used oil pump gears in an engine that’s being overhauled. New gears come with new bushings, so the only “old” part remaining would be the oil pump housing. The oil pump housing can be measured to confirm that it is within limits and if it is, the pump is good to go until the next overhaul.


The next big component to be inspected (and possibly repaired) is the crankcase. This is the big aluminum casting that holds together the lower end rotating crankshaft timing gears, camshaft, magnetos and cylinders. 

This complex and massive aluminum casting must first be checked for cracks by using a non-destructive fluorescent dye penetrant process, often known as Zyglo testing. 

With the case thoroughly cleaned and dry, the dye (a penetrating fluorescent oil solution) is applied to all the surfaces of the case and allowed to soak into any potential cracks. The surfaces of the case are then thoroughly cleaned. Existing cracks will retain some of the fluorescent material. 

When the case is inspected with a black light, the fluorescent material remaining in a crack will glow in a yellow-green color revealing cracks or porosity in the metal. If problems are found, the case can be sent to a company that specializes in welding and machining engine cases to new limits.

Using a black light to check for cracks in the crankcase.

If there is no evidence of cracks, the case is checked to ensure that all mating surfaces and areas that support rotating parts, such as crankshafts, camshafts, etc., are straight and not distorted.

Cylinders, valves, valve guides and other mechanisms

Next, it’s on to the cylinders, the most heat-stressed components in an internal combustion engine. Once thoroughly cleaned, all areas of the aluminum cylinder heads are checked with the Zyglo test I mentioned earlier. 

If no cracks are detected, the valves and valve guides are inspected and machined. Excessive wear in valves or valve guides will require replacement. The steel valve seats must meet minimum dimensional standards. If not too worn, valve seats and valves can be precisely re-ground to recreate factory specifications. 

Next, the valve drive mechanisms and their supporting components, rocker arms, bushings and supporting bosses are inspected using the previous techniques.

Within limits, steel cylinder barrels can be re-machined back to serviceable or new limits. The area where the aluminum head and the steel cylinder barrel are connected is closely checked for leakage. A leak at this juncture means the cylinder is not repairable. 

The next step is to measure the bore of the cylinder for wear and condition and, for some cylinders, choke. Choke is a difference in diameter between the hot top end of the cylinder barrel and the cooler lower base of the cylinder. Cylinders can be re-bored to a permissible oversize limit or chrome plated back to new limits by a company that specializes in cylinder work.

Reconditioned cylinders, with new pistons and piston rings, ready for installation. 
Assembling the engine

After days and days of preparing all the engine components for reinstallation, it’s finally time for the fun part of assembling the engine. 

All the new and reconditioned parts ready for assembly.

The process begins with mounting the crankshaft to an engine stand vertically by securing the propeller flange to a mating surface located at the top of the engine stand. Then, an assembly lubricant is applied to the rod bearings. The connecting rods are bolted to their crank journals with new high-tech rod bolts and nuts. 

Crankshaft and connecting rods mounted on an engine stand.

The bolts are carefully tightened to a specific tightness torque with a special calibrated torque wrench and double-checked by a second technician. This two-step verification system will be used throughout the entire buildup process for any critical mounting hardware—smart! 

Next, the engine case, with the pre-lubed camshaft, camshaft bearings, valve lifters and main bearings, is mated to the crankshaft and secured by properly-torqued case bolts. 

It’s time to install and properly index the magneto, cam timing gears and oil pump, and mount the accessory case cover at the back of the engine. The oil pickup is installed and the oil sump case is bolted on.

Next, the cylinder and pistons are installed, and all cylinder base bolts are torqued to the correct values. The pushrod tubes, pushrods and rocker arms that actuate the valves are installed. Then, it’s on to installing the intake manifolds, magnetos and fuel system, including the engine-driven fuel pump (if required). 

Cylinders, pistons and valve-actuating rocker arms.

As these components are installed, the technician is constantly rotating the engine on the stand, checking for any excessive resistance, proper running clearances and timing of critical components such as valves and magnetos. Lots of stuff, huh? 

With all this completed and double-checked, the engine is painted. Now the engine is ready to run, either in a test cell or installed in the aircraft.

Overhauled engine ready for test run before shipping to customer. 
The paperwork

A reputable overhauler will supply their customer with the following documents and services with the newly-overhauled engine:

1. A teardown report stating the condition of all components when the engine was disassembled.

2. A thorough logbook entry specifying the limits to which the engine was overhauled (such as service limits, new limits, etc.), including a description of all work performed, a complete list of all new parts installed, and supporting certification paperwork for each new part.

3. Yellow tags verifying the identity and airworthiness of all reconditioned components installed in the engine.

4. Statements related to test flight or test run.

5. Any supporting warranties for components not repaired or rebuilt by the overhauler, such as starters, alternators or fuel system components.

6. A clear warranty policy stating what is covered, when the warranty begins and expires, and a payment policy should the warranty need to be enforced.

ADs and Service Bulletins

If defects are discovered over the years a particular model of engine is in service, ADs and Service Bulletins are issued. Some require immediate attention and others must be completed at overhaul. It is important to ensure that all ADs and Service Bulletins are complied with during the overhaul process. 

I think we’ve gone over enough for now. With general overhaul procedures covered, next time I’ll explain the three choices for where this work can be done: a local A&P, an overhaul specialist and the engine manufacturer’s factory. Until then, fly safe!

Industrial designer and aviation enthusiast Dennis Wolter is well-known for giving countless seminars and contributing his expertise about all phases of aircraft renovation in various publications. Wolter founded Air Mod in 1973 in order to offer private aircraft owners the same professional, high-quality work then only offered to corporate jet operators. Send questions or comments to .

Proper Entry Procedure: Fitting & Adjusting the Piper PA-28 Entry Door

Proper Entry Procedure: Fitting & Adjusting the Piper PA-28 Entry Door

Before you can properly seal the door, you must ensure it is fitting properly. Here is a step-by-step guide for removing, checking and adjusting the door.

The only way to properly adjust a door on a Piper PA-28 series aircraft is with the door seal removed. Only then will you know if the door is fitting properly. The following procedures should be accomplished before installing a new seal, and they can only be done by or under the supervision of an A&P mechanic.

Remove the door

Remove the screw, step bushing and washer attaching the doorstop to the doorsill plate. Remove the cotter pins, clevis pins and washers from door hinges. Set the door aside on a blanket or other protective covering.

Remove the old seal

There is no easy way to remove the old seal and adhesive, but I’ve found that using an electric heat gun (such as those used for paint removal) aids this process considerably. First, locate the seal joint and with the heat gun apply heat to the seal and carefully begin to lift the seal from the edge of the door. Continue applying heat in the apex of the seal as you lift it from the edge of the door until you have it completely separated from the door.

Remove the door seal adhesive

Removing old adhesive can be performed using one of two methods. One way is to use a small (three-inch) brass brush on a drill motor and literally peel the adhesive off the door. This method does require that the door edge be repainted. (An aerosol such as Krylon paint may be used to repaint the edge of the door, and it stands up well over the years.)

The second method is to dissolve the adhesive with a product called Goof Off. Goof Off, touted as “The Miracle Remover,” will not affect paint or Plexiglas.

I’ve found that applying heat to the old adhesive and then wiping the area using a rag saturated with Goof Off will remove the residue. Use caution to prevent combustion. Ensure any Goof Off liquid remaining on the door has fully dried before reapplying heat from the heat gun.

When the door edge is cleaned up, you are ready proceed with the adjustment.

Check for wear in the hinge

Over the years, the eyebolts and clevis pins (door hinge system) can become worn to a point where the door will sag and not close or seal properly. It’s imperative that these parts be checked for wear before proceeding.


A good way to check the parts for wear is to slightly open the door and see if you can raise up on the door. There should be no movement (or very little movement) of the door vertically.

If you can raise up on the door, the eyebolts and clevis pins are worn out and should be replaced. (The tolerance when new is only three thousands of an inch.)

These items are not expensive, yet they are critical to properly closing and sealing the door. Aircraft Door Seals sells eyebolts and clevis pin sets. The new eyebolts and clevis pins come with complete instructions for installation and can be replaced in less than five minutes.


Reinstall the door

Place the door into position over the eyebolts and install the washers and clevis pins in the door hinges. (Do not reconnect doorstop to the doorsill on the fuselage at this time.) Close the door and secure the upper latch.

With the door closed and latched, verify the front edge of the door is flush with the fuselage. Many times the door will not be flush; instead, it will actually be fitting inside of the fuselage anywhere from 1/8 inch to 3/16 inch. It must be flush with the fuselage before you proceed.

If you find the door is not fitting flush, this may be corrected by the installation of spacers (washers) under each eyebolt (or as required) which will move the upper or lower portion of the door and enhance the door’s fit. The washers you’ll need are AN960-516 (thick) and AN960-516L (thin)—typically, just one or two under each eyebolt will correct the fit.

To remove the eyebolt, you must remove the door. Just inside the cabin in front of the door opening (behind the interior trim), you will find a 5/16-24 nut for the upper and lower eyebolt. Slide a half-inch box wrench behind the upholstery, placing it over the nut.

Using a crescent wrench on the eyebolt, unscrew the eyebolt (counterclockwise) and remove it. It is helpful to have an assistant place the washers on the eyebolts so you do not have to move the wrench and nut. Install one or more washers as required on the eyebolt(s) and reinstall. Do not over-tighten—just snug is sufficient.

Reinstall the door and verify the front edge of the door fits flush with the fuselage. If not, repeat this procedure using thick and/or thin spacers until it does fit flush.

Note: Many times the factory installation leaves a little to be desired. With the door fully closed, inspect the clearance between the edge of the door and outer periphery of the fuselage door opening. Many times I have found the edge of the door skin actually hitting the fuselage, especially at the front edge. You should have a minimum of 1/16 inch clearance. If not, file the edge of the door until it has the proper clearance.

Adjust the door

If the door does not fit flush with the fuselage around the entire opening, start with the adjustment of the main latch by loosening the two flat head screws and move the striker plate (in or out) as required. Re-tighten the two screws. Repeat this as necessary until the door fits flush. The door should have a 1/16 inch to 1/8 inch clearance around the entire edge of the door and fuselage.


On early Piper models (pre-1968) I’ve found the latch clevis pin to be bent, which will prevent the door from latching properly. If it is bent, it must be replaced. Aircraft Door Seals stocks this clevis pin.

To provide the proper vertical adjustment of the door, insert the necessary washer combinations between the cabin door hinge(s), clevis pins and the fuselage eyebolts. Also verify that the fittings riveted to the door have not been bent. The fittings forming the portion that fits over the eyebolts should be straight.

Adjust the upper door safety latch

To adjust the door upper (hook) latch, remove the two screws from the latch plate on the top of the fuselage door opening. Remove the plate and rotate the loop clockwise or counterclockwise (a small amount of WD-40 on the threads will help) to make necessary adjustments.


Replace the latch plate and secure with the two attachment screws. Check the fit of the door.

Many times the upper latch hook can become bent and actually hit the upper portion of the door opening (fuselage). The upper hook should be centered in the upper opening. If not, using vise grips, clamp the hook at the point where there is a slight bend in the hook and slightly bend the hook until it is centered in the opening. Caution: When bending the hook, support the hook with your thumb in the area where you are bending. This will prevent the latch from being damaged.


Check the fit and make final adjustments

When the door is properly adjusted, there should be approximately a 1/16 to 1/8 inch gap around the outer periphery of the door between the door edge and the fuselage.

Insert the cotter key(s) in the clevis pins and bend the cotter key ends around the clevis pins and trim off the excess cotter key length as required.

It is not uncommon for the forward top edge of the door to not fit totally flush with the top edge of the fuselage. This condition is due to the variables in the assembly process of the door. Many times I have found it necessary to adjust the fit of this portion of the door by slightly bending the door upper edge.

This procedure will not damage the door and has been done by the factory for years, but it must not be done with the door installed. It is best done with the door lying flat on a blanket and manually massaging the upper portion of the door with your knee until you are satisfied with the fit.

The entry door has been cleaned up, fitted and adjusted, but you’re not done yet. Follow the manufacturer’s instructions to the letter for successful installation of the new door seal.

Dick Russ is a multi-thousand-hour commercial, multi-engine and instrument-rated pilot. He’s also a flight test engineer and an A&P/IA who has restored many Pipers. In addition to his career as a freelance writer and aviation business owner, he was senior engineer on the Shuttle Enterprise Approach and Landing Test Program at Edwards AFB. Russ holds three patents on aviation components. Send questions or comments to . 


Aircraft Door Seals
The Straight Dope on Fabric-Covered Airplanes

The Straight Dope on Fabric-Covered Airplanes

Fabric-covered planes in good condition are available, but you need to know what to look for.

Aircraft have been covered in cloth since the Wright Brothers took flight, and the material had to be as light as possible yet strong enough to withstand the demands of flight. 

The standard material used in the early days was cotton or linen. Vintage aircraft typically had wood wings and steel tubing used in the fuselage. 

The materials

The use of cotton or linen cloth is still approved; however, it is rarely used today because synthetic materials and improved processes are available. 

Synthetic materials and associated application processes not only reduce the amount of labor required, but also provide longer life, resistance to rot and fungus, and are safer in the case of fire (during material application, and while in flight). 

Polyester cloth specific to aviation applications is almost exclusively used in the recovering (or initial covering) of an aircraft today. Fiberglass cloth has been used as well, and other synthetic materials have been experimented with and/or are in development. 

The most important difference between newer synthetic materials and the original cotton and linen cloth is the fact that cotton is more difficult to work with. In addition, cotton is subject to attacks by fungus, mildew, chemicals (such as acid rain) and is susceptible to damage from rodents and sunlight. 

While synthetic fabric is deteriorated by sunlight too, it has better resistance to the effects of ultraviolet light. Synthetic fabric is also resistant to fungus attack, and while it can be damaged by chemicals, it is more resistant to damage than cotton. 

Cotton and the compatible nitrocellulose dope used to stiffen the fabric in the recovering process are flammable. Nitrate-based dope is extremely flammable even after it dries, and is seldom used today.

Synthetic fabrics sometimes call for cellulose acetate butyrate dope according to the STC, but oftentimes a material that is less flammable and more suitable to the synthetic fabric process is used. 

A significant factor regarding polyester cloth is that the tautness of the fabric is controlled by heating the fabric with a temperature-regulated device similar to a clothes iron. Application of dope or sealant materials will not appreciably shrink polyester, as is the case with cotton fabric. 

Aviation-specific synthetic fabric can be much stronger than cotton fabric. This is a key issue in the pull testing (strength) of the raw fabric to determine continued airworthiness years after the initial fabric application process has been completed. Fabric is considered airworthy until the strength degrades to less than 70 percent of the original design strength. 

The FAA testing specification has always been in reference to the original material the aircraft was designed and certified with. Aircraft produced under the CAR 3 rules were approved with cotton or linen cloth of different grades depending on wing loading and maximum airspeed limitation. For example, aircraft could be certified with grade A cotton, intermediate cloth or glider cloth, depending on the never exceed speeds and wing loading, and then could be later recovered with a fabric of a higher rating. 

The process

Working with cotton or linen requires special techniques and processes for a good-looking and airworthy cover job. When recovering an aircraft, the structure has to be carefully inspected and all defects repaired; then it can be primed and protected prior applying the fabric. 

The fabric has to be cut and sewn to the shape of the wing or fuselage and cemented or tacked into position. After the fabric is installed and secured to the frame, it’s permanently attached to the wing ribs with a special lacing cord using a designated knot. 


The spacing of the rib stitches varies according to the VNE (never exceed) speed of the aircraft and if the area is in the propeller slipstream or not. Some aircraft use screws or fabric clips in place of the rib stitching. 

After the rib stitching, the next procedure is the application of cloth tape to cover the stitching and the installation of inspection rings, grommets and patches in various locations to protect the underlying fabric. 


A plasticized liquid lacquer (i.e., dope) is applied to the fabric in several applications initially by brush and then by spray gun to form an airtight and waterproof bond that also tightens and stiffens the fabric materials. 

The proper fit of cotton or linen fabric prior to doping is important, as extremely taut fabric caused by multiple applications of dope will shrink and distort or damage the underlying structure requiring removal, repairs and reapplication of the fabric. 

Proper health precautions must be followed when applying doping agents, especially when applying urethane in a spray form as it is extremely toxic. 

Multiple applications of various mixtures of dope are applied generally by spray gun. Mixtures may include dope with silver metallic compounds for resistance to light, dope with fungicide for resistance to fungus, and pigmented dope for the final color applications. 

Purchase considerations

An aircraft covered with polyester fabric—if it is applied according to STC, properly maintained and kept in a hangar—can have an almost indefinite life. However, when considering the purchase of a fabric-covered airplane, it is important to seek a mechanic that is familiar with this type of aircraft and knows what to look for. 

With the cost of a complete recover job for a simple airplane such as a Piper J-3 Cub or Piper PA-18 Super Cub in the $30,000 to $40,000 range, you must be certain of the condition of not only the fabric, but what lies underneath. 

As with most airplane purchases, it is always good to look for an aircraft that is in excellent condition and pay the asking price rather than look for the bargain. That bargain plane could require recovering that would make the final cost exceed the value of the aircraft. 

Prior to contracting with a mechanic to do a pre-purchase inspection, there are areas which you can check yourself just to see if the fabric-covered aircraft is in a condition that you would consider purchasing it. 

Keep in mind that vintage tailwheel aircraft probably have had a few ground loops, with airframe and/or engine damage and major repairs. Damage history is almost a given—but what this means for the purchaser is that the repairs must have been done correctly and that the aircraft flies like it should. 

The first order of business is to check the aircraft records, including any FAA Form 337 documents, to get an idea of the history of the repairs done to the airframe and engine. 

After checking the aircraft records, including compliance with all ADs, it would be wise to make up a written list of items to check on a pre-purchase walkaround. Make notes of anything you have a question about. 

Start with the condition of the fabric, and what the finish looks like. Check for cracked and missing paint or dope that would allow sunlight to directly access the fabric. Look for ringworm in the fabric; this indicates that the paint job is failing and will cause the cloth to deteriorate in a short time if exposed to direct sunlight. 

Check for patches, noting any especially large patch areas—these would require a logbook entry, or possibly a 337 form indicating a major repair. If there is no logbook entry indicating a repair was made where a large patch is located, be suspicious. There could have been major damage to the airframe structure that was repaired improperly, or not at all. 


Wrinkles or sags in the fabric most likely point to structural damage. For example, a dent in the metal leading edge of a wing would cause a sag or wrinkle in the fabric that would be visible from the outside. 


Blisters or rough areas under the fabric along lower longerons are an indication of rust in the steel tubing. Other areas could also have blisters or rough spots, such as the horizontal stabilizer, elevator or rudder; water is often trapped in these areas and eventually causes rust or corrosion. 


A fabric-covered aircraft should have sufficient drain holes or grommets installed—not only to allow moisture to escape, but also allow air to circulate and expel any moisture created by condensation. 


With the owner’s permission, pull a few inspection plates off from under the wings, especially in the area where the lift struts attach to the spar. Use a flashlight to take a good look at the wooden spar around the bolt holes, checking for obvious defects such as cracks or splits in the wood.


Move the strut at the upper end and see if there is any evidence of movement between the spar and the lift strut attachment fitting. Whether the spar is wood or metal, any movement is not good and could cause the spar to crack in this location, which would be an expensive repair or replacement. 

While the inspection plates are off, take a look up through the wing. Sunlight is the number-one enemy of fabric, and any daylight showing through the upper wing surface means a reduction in the useful life of the fabric. A very dull indication of light is okay, but if you can see a shadow of a person’s hand blocking the sunlight, then there probably isn’t enough light-resistant silver or pigmented dope remaining on the fabric. 

While the inspection plates are off, take a look at the rib stitching to see if the lacing cord is intact. Rodents have been known to get into a wing and chew the lacing cords, requiring expensive repairs. Rodents and birds can destroy an aircraft, especially if the structure is compromised by droppings or if drain holes are plugged with debris. 


While on the subject of wing ribs, note that over the years, several aircraft accidents (and at least one fatality) have occurred as a result of missing rib nails that secure the rib to a wooden spar. 


Another problem with wings and ribs is that of dissimilar metal corrosion when steel clips are used to secure fabric to the individual aluminum wing ribs. 

Since tailwheel equipped aircraft are sometimes involved in ground loops, check the wingtips for damage. Look at the fabric to see that there are no scrapes or tears, and check the wingtip for cracks or damage by looking up and out toward the tip through an inspection hole near the wingtip. 

Take a look at the lower rudder area and tail post for signs of damage such as loose fabric, wrinkles or sags, and possibly bent tubing from a hard landing on the tail. 


Get up on a stepladder and check the center section and inboard wing fabric directly in the propeller slipstream. This area sees a lot of vibration and heavy airstream deflection from the propeller, which induces wear/chafing and weakening of the fabric. 

The use of a suction cup on the fabric—attempting to pull up on the fabric in this area—is a simple test to see if the fabric is weak and/or not secure, requiring repair or replacement. 

Final thoughts

When evaluating a fabric-covered aircraft, you really need to take enough time to go over the paperwork and the aircraft completely. Repairs to structure or a complete recover job are considered major repairs; they are expensive, and legally must be done by (or supervised by) an experienced and licensed mechanic with inspector status to complete the FAA Form 337. 

Recovering a Type Certificated aircraft is a job I recommend you leave to the experts. Errors in the fabric replacement process are easily made—and these can be difficult and costly to correct. Mistakes may even require starting the job over. 

Replacement of aircraft fabric is a big job because it never is just a plain recover job—there may be repairs required along with the preparation involved, such as completely disassembling the fuselage frame and sand blasting the fuselage, inspecting for damage and rust, and applying dope proof primer. 


Woodwork requires proper preparation with cleaning, sanding and application of special dope proof sealer. 

Multiple repairs to the structure, to include welding prior to the recover process, are more common than one may anticipate. These repairs can become overwhelming unless the job is properly planned and executed by an experienced person. 

How much a recover job costs depends on the process used, how many repairs are required prior to covering, and if you are able to assist in the process. 

Poly-Fiber publishes an estimated cost of materials for recovering a Cub as approximately $5,500, and estimates the time required as a month. These figures are probably optimistic, especially if you don’t have experience or close supervision. 

When considering the purchase of a fabric-covered aircraft, look for a well-maintained aircraft with a quality fabric cover job. A quality job should last 20 years or more, depending on environmental conditions and exposure to sunlight. Any bargain-priced fabric-covered plane will most likely cost more to own. 

Vintage tailwheel aircraft can be a joy to own and fly. Enjoy the experience, buy the best—and leave the recover job to someone else!  

Michael Berry is a former aircraft repair shop owner. He is also a multi-engine rated ATP (757/727), A&P/IA, airplane owner, turbojet flight engineer and Part 121 air carrier captain. Berry has over 15,000 pilot hours. Send questions or comments to .


Consolidated Aircraft Coatings (Poly-Fiber)
Place, Peel, Press & Spray

Place, Peel, Press & Spray

The pros and cons of using decals and stencils to apply aircraft graphics.

You’ve just repainted your airplane and it’s beautiful. There’s just one detail keeping you grounded: applying the required N-numbers and placards. 

According to the dictionary, a placard is a “sign for public display.” So, what’s the best method to publicly display your aircraft information? Decals or paint? 

Dried-out decals

I’ve never liked decals, particularly after seeing so many cracked and peeling from airplanes sitting in the sun on the flight line, but they do have some advantages. 

First, almost anyone with patience can apply them. If you mess up, peel it off and try again. Another benefit is that they can be easily removed. If there’s a chance you may change your N-number, decals are the way to go. 


There’s one caveat, though: the paint around decals can fade, so after a few years it may not look so great if you make a change. (Kind of like a girl with a suntan from one bikini who then wears another with a different cut. You can tell where the sun’s been, and where it hasn’t.)

Unless you have the cash to hire a professional painter, or you’re an artist yourself, you’ll want to use decals for any complex designs. Unusual or personalized images can be sent to an aviation graphics company for printing on decal material.


Soap is for the kitchen dishes

When applying a decal to an airplane, many people suggest using soapy water—often a mixture using common dish soap—to make a slippery surface for the decal to float upon. This allows for fine adjustment of the decal’s position and for air bubbles trapped underneath to be squeezed out. 

I don’t think soap is good for adhesion, and I have to wonder if the reason many decals are peeling and cracking is that they’ve been degraded by a sunbaked soap film. If you use my method, you shouldn’t have any bubble problems and you won’t need to make last-second, soapy adjustments to your decal’s position.

My method to apply decals

1. Use a small piece of masking tape to place the decal where you want it, with the backing material against the aircraft. The decal material is made of three layers, a heavy backing, the decal in the middle and a light protective paper. You’ll be able to see through the light paper side to ensure its orientation.

2. Step back and look at the position carefully. Compare what you see in front of you to your photos or design plan. Is the decal straight? Does it match the “line” of your plane? It might look better if it matches the airplane’s lines versus being dead-straight.

3. Adjust the decal until you are absolutely sure that’s where you want it, then completely tape down the top edge.

4. Flip the decal up, making a hinge of the tape. Crease the tape so it moves easily.

5. Have a soft, clean cloth within reach and start peeling the backing off the decal from the top, next to the tape hinge. Press down that topmost edge of the decal and use the cloth to smooth the decal as you slowly peel the backing material off. The cloth will help it go down smoothly without any bubbles. Work slowly, and pull the backing material off in a straight line.

6. When the decal is fully applied, remove the protective paper and masking tape, and rub the decal gently with the cloth.

A second pair of hands helps during any decal application, and is essential for large decals—one person pulls off the backing, while the other smoothes the decal. 

For really large decals—such as 12-inch N-numbers, which could be five or six feet long—it’s best to cut the decal into manageable pieces. After taping down the top edge (step three, above), cut vertically between the numbers. The decal will look like a row of teeth. Then apply one number at a time.

Placarded information

Aviation graphics companies sell sets of decals for all the placarded information needed inside and outside your particular aircraft, such as “No Step,” “Avgas Only” and “Fasten Seat Belts.” Do I really need a “No Smoking” decal on my instrument panel? Evidently, it’s required. 

Use the same tape-hinge method described earlier for these small decals.

Stencils and paint

Painted graphics look better, especially after years under the sun, but painting also takes far more effort (or money, if you want someone else to make the effort). 

First, you must apply stencils and protect nearby areas of the aircraft from overspray, then mix up and spray toxic paints, remove the stencils and protective materials, and clean the spray equipment. The stencils, paint and rental of a spray gun cost far more than decals. 

Painted markings are also almost impossible to change—you’d have to repaint the background color first—so be sure before you start spraying. 


If it’s so much effort, why paint? 

It looks really good and stands up to the elements when done right.

Large stencils can cost hundreds of dollars—quite a bit more than masking tape—but modern stencil materials give a much sharper edge and don’t allow paint to bleed underneath. 

I think it’s worth the cost. This is especially true when painting on fabric covered aircraft with ribs and stitches to cover. The difference between figures sprayed through computer-cut stencils and those done using masking tape is obvious, at least to me.

Some painters still prefer to use tape to mask out N-numbers and insignias for painting, citing the cost and difficulty of handling large stencils. But, in my opinion, that’s a tradeoff of quality for cost. You have to be a real artist to create straight, properly aligned letters with a roll of masking tape, and there’s inevitably a few spots where the paint bleeds.


If you do use masking tape, run your thumbnail over the edges to make sure they are pressed down completely. And, no matter how well you think the tape is adhering, paint will bleed under it every time if you apply the paint too heavily at first. A very light, almost dry coat will seal the edges and prevent bleeding when you apply a heavy coat to finish the job.

My method for applying stencils is the same as it is for decals. The only difference is the additional step of removing the middle layer—the one cut in the shape you want to paint—so the paint can reach the surface.

Really large stencils might take three people to apply: two to pull off the backing material and one to smooth the stencil.

Take a second look

I ordered two identical stencils for my aircraft. You would think the company would set up the type (in this case, a large N-number), hit “print 2,” and they’d be spit from the stencil-cutting machine exactly alike. Well, they weren’t. 

The painter placed the stencils on my aircraft according to my instructions and sprayed. Only after he peeled them off did we see that the spacing of the letters was incorrect on one. The letters were too close together.

My pilot friends say, “no one will ever notice,” and maybe that’s true—but I noticed it immediately. I could have fixed it by increasing the spacing myself, if only I’d seen it earlier. The lesson here is: stand back and take a long look before slinging paint. 

I’m sure there are decal people, stencil people, masking tape people… and everyone has their own opinion. You can make your own choice. That’s part of the fun of having your own plane, isn’t it?

What methods have you found work best on your airplane? Visit the forums at PiperFlyer.org to share your successes, upload your photos, and get more ideas.

Dennis K. Johnson is a writer and a New York City-based travel photographer. He flies sailplanes whenever possible and is the owner of N105T, a newly restored Piper Super Cub Special. Send questions or comments to .

Papa’s Got a Brand New… Fuel

Papa’s Got a Brand New… Fuel

Swift Fuels’ 94 Octane Unleaded Avgas

Earlier this month I burned 25 gallons of Swift Fuels’ 94UL unleaded Avgas in the 180 hp Lycoming O-360 in my 1960 Piper Comanche, Papa. 

Swift Fuels of Lafayette, Ind. has submitted its 102 octane unleaded (102UL) Avgas to the FAA for testing in the Piston Aircraft Fuels Initiative (PAFI) program, but it also announced in mid-2015 that it was producing a 94 octane unleaded (94UL) Avgas. 

In the last year and a half, 94UL hasn’t gained much traction even though it’s approved for operation in a wide range of GA engine and airframes. 

94UL is produced to ASTM Standard D7547, the specification for hydrocarbon unleaded aviation gasoline. This lead-free Avgas was developed at the request of the military in 1994 for use in its drone fleet. 94UL is a stable fuel with a “tank life” of two years. 

I am looking forward to the day when Avgas will be free of tetraethyl lead (TEL), and when I saw that Swift offered a lead-free Avgas that I could legally use, I wanted to try it. What I found was very interesting.

By the end of my flight testing I hadn’t seen one iota of discernible difference in any engine parameter—EGT, CHT, manifold pressure, rpm or oil temperature—between the 94UL and 100LL Avgas. 


Data collection

The data I’ve captured is by no means an exhaustive test. I haven’t done an extreme heat or extreme cold temperature starting test. I haven’t done a high altitude (18,000 feet MSL) operational test. I haven’t done an in-flight restarting test. Nor have I done a fuel system compatibility test. 

But thanks to the data collection feature of my Electronics International CGR-30P and 30C engine monitor, I could collect and plot the engine data gathered during the three test flights using EGView from EG Trends. 

I also asked Joe Godrey and Savvy Analysis to check my plots. He verified my findings.


Preparing for the tests 

There is one 30-gallon bladder-style fuel tank in each wing of my airplane. The fuel selector valve has three positions: left to the engine, right to the engine, and off. There’s no both position. 

After flying the right tank empty and sumping the remaining unusable fuel out through the system low point drain, I paid Rabbit Aviation Services at the San Carlos Airport (KSQL) $118.37 to pump 26.6 gallons of 94UL into the right-wing tank. 

I also topped off the left tank with 8.4 gallons of 100LL ($38.22). That crunches down to 100LL at $4.55 a gallon and 94UL at $4.45. (Vendors set the pump prices; when buying from Rabbit there’s minimal direct cost savings.) The fuelers at Rabbit asked if my airplane was approved for auto gas or 94UL Avgas before dispatching the 94UL truck. 

Initial observations

94UL smells different than Avgas and is clear. I checked the two fuels for weight. The 94UL is lighter at 5.79 pounds/gallon than the 100LL at 5.94 pounds. 

I flew three one-plus hour flights, switching back and forth between the left and right tanks. 

I switched during a full power climb; I switched with the mixture leaned to peak EGT on the first cylinder to peak; and I switched during my normal cruise power and mixture settings while level at 5,500 feet MSL. I also switched on descent and while idling before flight and after landing. 

In addition to collecting the engine parameters digitally, I also watched for any EGT difference in the seconds following the switches. I never saw the numbers change.


Users’ reports

John Poppy at the Portage Municipal Airport (C47) in Portage, Wis., a popular fueling stop near AirVenture, said he’s heard “zero negative feedback” about 94UL. 

Poppy has a 1,000 gallon tank and says he pays two cents a gallon for shipping for the five-hour drive from the Swift production plant in Lafayette, Ind. Poppy sells 94UL for $3.35 a gallon—59 cents per gallon less than his 100LL. 

Poppy told me that one customer who flies a Cessna 182 has been using it for over a year while commuting to another state. According to Poppy, the customer’s mechanic asked if he had taken his engine apart and cleaned it after pulling the cylinders for a top overhaul. 

Rich Volker of RV Airshows burns it in the 600 hp Pratt and Whitney R-1340 that powers the Harvard Mk IV he flies in his airshow routine. Volker told me he flies his routines at full power and in his opinion, his engine can’t tell the difference. 

Dennis Wyman runs the engine shop at G&N Aircraft in Griffin, Ind. Wyman told me that his experience is that running 94UL results in less deposits on pistons and valves. In his experience, the switch between the two fuels is transparent. 

The only change Wyman has seen is that the combustion chamber of an engine that uses 94UL looks slightly darker than a 100LL chamber. Can you use 94UL?

You can use 94UL is your airplane fits into one of the following options:

• Airframe/engine combinations that have an Auto Fuel STC (e.g., an STC from Petersen Aviation);

• Airframe/engine combinations OEM-approved for auto fuel (e.g., ultralights, LSAs and experimental aircraft);

• Airframe/engine combinations Type Certificated to operate on Grade 80 (listed as Grade 80/87 in ASTM D910) or Grade UL91 (ASTM D7547) Avgas; (Note: If the fuel data plate on the engine lists 80/87 as the fuel, you can legally use 94UL without an STC. This includes Piper singles such as PA-18, -20, -22 and 150 hp PA-28s.) 

• Airframe/engine combinations Type Certificated to operate on minimum 80 octane or lower (e.g., 73 or 65 octane) Avgas; or

• Airframe/engine combinations with an Avgas STC purchased from Swift Fuels.

The engine data plate on my Lycoming O-360-A1A specifies 91/96 octane fuel, yet my Piper PA-24 Comanche had never been approved for an auto fuel STC. My only avenue to use 94UL was buying an Avgas STC from Swift. 

Where can you get 94UL?

Per the user map on the Swift Fuels website, there’s only one public source for 94UL west of the Mississippi River, and it’s in California. 

There are also 14 that are cited as “private users.” The 18 other public outlets for 94UL include three in Florida, one in South Carolina, one in Ohio, one in Missouri, four in Indiana and eight in Wisconsin. (Note: If you would like find out more about setting up a 94UL station, contact the folks at Swift. They have a team that will tell you how to get started.)

One of the potential roadblocks between availability and pumping 94UL at your airport is tankage. Most airports now have two tanks—one for jet fuel and one for 100LL. One option for adding a third is installing a box station from U-Fuel in Elk Mound, Wis. 

U-Fuel offers a split tank—94UL on one side and 100LL on the other. It appears that split models have the same footprint as existing single-fuel models. 


94UL is here now; PAFI fuel is a few years away

Since most privately owned and operated airplanes in the GA fleet can safely burn 94UL, and since Swift sells it for less than today’s 100LL, Swift’s 94UL seems like a winner. 

No one knows when the new unleaded 100 octane Avgas will be produced—it’s still being tested in the Piston Aviation Fuels Initiative (PAFI) program. 

The PAFI program is scheduled to complete the fuels testing in 2018, but there could well be a time lapse between the approval date and the production and delivery to your local airport. 

Based on my testing and my belief that TEL creates a wide range of problems in our air-cooled engines, I would be burning unleaded aviation fuel today if there was a pump with a Swift 94UL placard close by. 

Steve Ells has been an A&P/IA for 44 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Templeton, Calif. with his wife Audrey. Send questions and comments to


Engine monitors and cluster gauge replacements
Electronics International – PFA supporter


EGView software – data analysis tool
EG Trends Inc.


Engine rebuilding, engine overhaul and engine sales
G&N Aircraft, Inc.


Auto fuel STCs
Petersen Aviation, Inc.


94UL fuel service (West Coast)
Rabbit Aviation Services, Inc.


Savvy Analysis – engine monitor data organizer
Savvy Aircraft Maintenance Management, Inc.


94 octane unleaded Avgas, Avgas STC
Swift Fuels


Aviation fuel stations


Further reading
FAA PAFI program
Q&A: Pitot Static Checks for a Cherokee 180 & Apache Stabilator Torque Tube Inspection

Q&A: Pitot Static Checks for a Cherokee 180 & Apache Stabilator Torque Tube Inspection

Q: Hi Steve,

I need more information on what my mechanic calls “pitot static checks.” I ask because he said I need them every two years—but then said only one is needed if I don’t fly IFR.

I am partway through my private pilot training and am using my dad’s Piper Cherokee 180. He said I could fly it as much as I want if I pay for the maintenance and upkeep.

I think it’s great that I get to fly the same airplane every lesson. I started out renting at a flight school and I personally didn’t like when I had to flip-flop between different airplanes. I think it made it harder for me to concentrate fully on the flying part.

But I’m afraid Dad hasn’t kept up with the maintenance on his Cherokee. For instance, the last pitot static check I found in the logbooks was over 10 years ago. I know who was doing his annuals and decided to go to a nearby well-established shop for the first annual I’m paying for.

So far they haven’t found any big-ticket items (whew!) but there have been plenty of catch-up items. I’m okay with that, because I’m going to be loading my family in this airplane and I want to be able to feel like it’s ready.

That’s my story. Now, the pitot static test?

—Learning Larry

A: Dear Larry,

Welcome to the world of flying. I feel like you’ve already made some good decisions regarding your training and the importance of having confidence in the maintenance work done on your airplane.

Unfortunately, there have been and continue to be “soft” annuals performed on a small number of airplanes every year. I’m glad you have resolved to take the steps required to get your dad’s airplane completely airworthy.

The pitot static system check you’re asking about is two separate checks. Both checks are spelled out in FAR Part 91, “General Operating and Flight Rules.”

The first rule is sometimes referred to as the IFR rule. It ensures the altimeter is working correctly and that the automatic altitude reporting system in your airplane is working and within tolerances. If you never fly IFR, you don’t have to keep this one current.

This rule, under FAR 91.411, “Altimeter system and altitude reporting equipment tests and inspections,” says that no one can operate in controlled airspace while operating under IFR unless, within the preceding 24 months, “each static pressure system, each altimeter instrument, and each automatic pressure altitude reporting system has been tested and inspected and found to comply with appendices E and F of part 43 of this chapter.”

I’ll explain a little more about this mandate—but it’s important to realize that even if you’re flying in clear weather, this inspection must be current if you’re on an IFR flight plan.

In fact, I think it’s a good idea to get in the habit of filing IFR from time to time on all except local flights because it helps keep procedures sharp and maintains a pilot’s awareness of how the “system” works.

The second rule, under FAR 91.413, is the transponder rule. 91.413, “ATC transponder tests and inspections,” states: “No persons may use an ATC transponder that is specified in 91.215(a), 121.345(c), or Sec. 135.143(c) of this chapter unless, within the preceding 24 calendar months, the ATC transponder has been tested and inspected and found to comply with appendix F of part 43 of this chapter.”

While the transponder test is required for all aircraft, there’s quite a bit of national airspace where a transponder is not required. This airspace is spelled out in FAR 91.215, but realistically, keeping your transponder check up-to-date assures that your system (and the airplane) is legal to fly almost anywhere in the country. Easier to just “get ‘er done.”

Many maintenance shops can perform both 91.411 and 91.413 tests, provided they have FAA approval in the form of a repair station license for these tests.

Avionics shops, manufacturers of the airplane, as well as a few other places also have this equipment.

Some folks grouse a little bit about the costs—which range from $200 to $300 for both certifications—but it is important to realize that the equipment needed for certifying your system also should be recertified on a regular basis, and that costs the shop some bucks, too.

I hope that answers your questions.

Happy flying.


Q: Hi Steve,

My mechanic wants to remove the horizontal tail feathers off my old Apache for what he says is an inspection from corrosion of the tube.

What’s he talking about?

—Apache Al

A: Hi Al,

Your mechanic is talking about Piper Service Bulletin No. 1160. It was issued in 2005 and calls for an inspection of the stabilator torque tube for internal and external corrosion.

The torque tube is a steel tube that ro-tates on large roller bearings that are supported in two-piece housings securely bolted to the aftmost bulkhead in the fuselage.

Since the left and right stabilator “tail feathers” are not normally removed during yearly maintenance, and since corroded torque tubes have been found, I feel that this is an important inspection.

I had to remove the tail feathers on my Comanche to comply with AD 2012-17-06 that related to an inspection for cracks in the stabilator horn. I did the inspection called for in SB 1160 at that time. AD 2012-17-06 does not apply to your Aztec.

Since my Comanche had spent much of its life near Phoenix where corrosion and rust rarely occur, I didn’t have any problem pulling my “feathers.”

However, I did do my best to soak the tube with AeroKroil before and during removal. The key to removing my feathers was to go slow and continue to apply Kroil.

I twisted the feathers slightly at first, and then more and more on the tube, and eventually they slid off.

SB1160 provides both a minimum outside diameter for the torque tube (2.3113 inches) and a minimum tube wall thickness (0.161 inches).

If there’s any deviation due to rust, the tube must be replaced. The part number for the tube for your Aztec is 16067-00. I just checked with Piper and was told that part number 16067-00 is no longer available.

If your torque tube is airworthy, make sure to apply a protective coating after the inspection. If it isn’t, a used serviceable torque tube assembly may be available through a salvage yard.

According to Tom Pentecost at DSA Flightline Group, owner of Piper Parts Plus (P3), the replacement kit (p/n 652-579) listed in Table 1 on page three of the service bulletin is still available with a lead time of 100 days.


Steve Ells has been an A&P/IA for 44 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Templeton, Calif. with his wife Audrey. Send questions and comments to


Penetrating oil


Piper replacement kit 652-579
Piper Parts Plus (P3) – PFA supporter


Further reading
FAR 91.411 and FAR 91.413


Piper Service Bulletin No. 1160
PiperFlyer.org/forum under “Magazine Extras”
Researching the Regs: Owner Produced Parts

Researching the Regs: Owner Produced Parts

An in-depth look at FAR 21.9 and Advisory Circular No. 23-27 by aviation legal consultant and A&P/IA Kristin Winter

The FAA keeps an iron grip on the supply of approved replacement parts for Type Certificated aircraft. Replacement parts generally must come from the airframe, engine or propeller manufacturer, or from an approved source that has been issued Parts Manufacturing Approval, commonly referred to as a PMA. 

There are some other limited exceptions for what the FAA refers to as “standard” parts, such as nuts, bolts and other hardware manufactured under an industry standard such as AN (Army-Navy) or MS (Military Standard), or parts manufactured by a repair station. 

There is one major exception to the FAA’s tight grip, and that is the owner produced part. Owner produced parts are commonly used by the airlines, which often have a large fleet of the same or similar types of aircraft. 

Like the owner of a General Aviation aircraft, an airline often wants to avoid the high cost of commonly used parts from the original equipment manufacturer (OEM), so it will reverse engineer and produce batches of parts that are
then used in its fleet. An example might be landing gear bearings that wear
out frequently. 

The availability of owner produced parts appears to go back for decades, though the origin is unclear. As it is of biggest benefit to airline operators, there is a major constituency to make sure that owner produced parts remain an available solution for all aircraft owners and operators.

FAA standards and definitions

The FAA sets out the limitations on replacement parts in FAR 21.9. 

Paragraph (a)(5) provides that one type of approved part is one that is “[p]roduced by an owner or operator for maintaining or altering that owner or operator’s product.” 

This simple statement leaves lots of questions unanswered. One common question is: must the owner or operator physically produce the part themselves? Most GA aircraft owners may not be equipped or sufficiently skilled to make a part in their basement. Fortunately, the friendly FAA has provided an interpretation. 

When the FAA renumbered and revised Part 21 in 2009, it specifically made mention in the Federal Register that the interpretation memorandum issued on Aug. 5, 1993 was still operative. 

The answer to the first common question as to whether the owner/operator must physically produce the part is clearly no. The FAA memorandum states that “An owner would be considered a producer of a part if the owner participated in controlling the design, manufacture or quality of the part.” 

The memorandum goes on to provide five nonexclusive indicia that an owner “participated” in the production of the part (italics added):

1. The person provided the manufacturer with design or performance data from which to manufacture the part. (This may occur, for instance, where a person provided a part to a manufacturer and asked that the part be duplicated.)

2. The person provided the manufacturer with materials from which to manufacture the part.

3. The person provided the manufacturer with fabrication processes or assembly methods to be used in the manufacture of the part.

4. The person provided the manufacturer with quality control procedures to be used in the manufacture of the part.

5. The person supervised the manufacturer of the part.

Responsibility of owners, responsibility of mechanics

So what does this mean to our aircraft owner faced with the unavailability of a critical part, or who is suffering from cardiac arrest at the cost and time delay of obtaining the part from the original equipment manufacturer? 

It is important to keep in mind that it is the owner or operator’s obligation to produce a part that is airworthy, meaning that the part conforms to type design and is safe to install in the aircraft. 

The installing mechanic’s responsibility is only to make a reasonable assessment that it is an airworthy part and to install it properly. (It will likely help the mechanic feel comfortable if they are provided with a copy of the drawing, the specifications, and/or have been part of the process from the beginning.)


Ways an owner can participate

Two options for owner participation jump out of the memorandum on first blush. 

First, the owner can provide the part to an appropriate manufacturer (such as a machine shop) and ask them to duplicate it. 

The other option is if an owner supervises the production, which might involve working with the mechanic to fabricate the part. Supervision would not likely require an owner to stand there every moment, but to be reasonably available to provide supervision or answer questions. 

In practice, owner supervision might be a little difficult given the likely disparity of knowledge between the owner and the mechanic. However, if the owner is willing to certify in the logs that he or she supervised the production of the part, it is unlikely to be challenged.

FAR 21.9 put into practice 

So let’s look at some practical applications. Not long ago, I determined that it was time to replace the flap tracks on my Twin Comanche. I had spoken with another owner who had the same problem, and we agreed to pool our resources to obtain some owner produced parts. 

I obtained an exemplar track and sent it to a metallurgical lab for analysis to determine the proper material. The lab charged a bit over $200 for the testing and provided a formal report. The other owner produced a drawing of the part. 

Armed with material and drawing, we had a couple of ship sets made. The cost was about $75 each, and the sets were created in five working days (turnaround can vary depending on how busy the shop is), compared to a cost of over $300 each from Piper and a wait of unknown duration. 

We clearly met the first example of conditions that qualified me as participating in controlling the design of the part. (See photo, top of page 26.)

Some considerations 

One of the most useful options for the aircraft owner is the specific acknowledgement by the FAA legal memorandum that an owner may provide the part and ask that it be duplicated. 

There is one complexity here in that many machine shops can duplicate a part, but are not equipped to determine what material it was made from. That might mean that the owner will need to resort to the metallurgical testing lab as we did with the flap tracks. 

Consideration must also be given to whether the part had any protective coating which should be duplicated. This could mean having the completed part anodized or cadmium plated. 

All of this may make it uneconomical to use the owner-produced exception if one is simply trying to avoid purchasing an overpriced bushing from the manufacturer. 

This is an area where an active type club that maintains a database of parts that have been owner produced—and possibly test results, and even CNC programs—can be most helpful. There appears to be no requirement that participation in the design requires an owner to reinvent the drawing, material specs, etc.

Gray areas remain

There are some gray areas still, even with the FAA’s memorandum. Take, for instance, a retractable gear single with a loose bushing where the nosegear pivots. The boss in the mount is worn slightly oversized so that bushing is no longer a press fit. 

To use a new OEM bushing would require removing the engine, removing the mount and sending the mount out for repair. The cost could easily exceed $5,000. 

A repair involving an oversized bushing might be a cost effective solution, provided your mechanic is comfortable making that repair. 

As the owner, you send the bushing to the lab and sketch out a drawing with the dimensions that have the bushing .001 inch wider than the factory. 

With the material specification in hand and the dimensions, you may then have a machine shop fabricate one. I have done this with great success and the only way I could tell a new OEM bushing from the oversized one was to get out a micrometer. (See photo, bottom left.) 

Success here will require a mechanic comfortable with the oversized bushing being an acceptable minor repair, so it is important to discuss this with your mechanic before embarking on such a repair. 

It is not unreasonable for the mechanic to ask the owner to make a logbook entry that they provided a part produced under FAR 21.9(a)(5) and provide the information used for its manufacture.

Why not use a commercially available part?

Any discussion of owner produced parts seems to raise the question about whether an owner can just go and buy the part which is commercially available. 

A good example of this might be a wheel bearing which is frequently a standard Timken bearing. From Piper, that bearing is $110.24; the parts catalog even identifies it as a Timken 13889 bearing. One can likely get the same item from the local auto parts store or a bearing supply company for $25 to $30—but is that legal?

As an owner produced part, the interpretation seems to suggest that it is not, though to my knowledge that hasn’t been clearly addressed—especially in the context of Piper identifying the actual vendor part number. 

If the aircraft owner got out the calipers and confirmed that the auto parts bearing was the same size, number of rollers, etc., arguably that would qualify as participating in the quality control of the part. This is another gray area. 

But there is one more option. Fortunately with this example, McFarlane Aviation has already obtained a PMA for the bearing, so for $40 instead of $100, one can obtain a bearing with a PMA stamp. 


Substitute parts under Advisory Circular No. 23-27

Advisory Circular (AC) 23-27 provides information on using substitute parts for small, unpressurized aircraft Type Certificated before 1980. That includes most standard Piper airplanes. 

Note that the operative deadline is not when the aircraft was produced, but when it was certificated—so even a late model Piper Archer is going to qualify, as it was Type Certificated before 1980.

While a bit confusing in its applicability, this AC appears to provide an approval for parts substitution if such would be considered a minor repair or minor alteration and to provide the basis for a field approval if a major repair or major alteration is required. 

Directly applicable to our example is the provision that states that “You may substitute parts where a direct substitute for a part/material can be found under manufacturer part number, military specification, or other recognized standard, such as the SAE.” 

For most aircraft owners, AC 23-27 can provide a route for substituting an industry standard part for an OEM part which may no longer be available in a timely manner or for a reasonable price. Mil-Spec switches, SAE alternator belts, batteries, etc. can often be used under the guidance of this Advisory Circular without resorting to an owner produced part.

For those of us who cannot afford a new or nearly new aircraft and who don’t have the luxury of just dropping off our plane at the local OEM service center with the keys and the Visa card, FAR 21.9 and AC 23-27 can be helpful in keeping aircraft maintenance cost effective, while still meeting the regulatory requirements.

Kristin Winter has been an airport rat for almost four decades. She holds an ATP-SE/ME rating and is a CFIAIM, AGI, IGI. In addition, Winter is an A&P/IA. She has over 8,000 hours, of which about 1,000 are in the Twin Comanche and another 1,000 in the Navajo series. She owns and operates a 1969 C model Twinkie affectionately known as Maggie. She uses Maggie in furtherance of her aviation legal and consulting practice; she also assists would-be Comanche, Twin Comanche, and other Piper owners with training and pre-purchase consulting. Send questions or comments to .


Further reading
FAA Memorandum, Aug. 5, 1993
“Definition of ‘Owner Produced Part,’ FAR 21.303(b)(2)”
Advisory Circular No. 23-27,
May 18, 2009
“Parts and Materials Substitution for Vintage Aircraft”

Both documents are available at PiperFlyer.org/Forum under “Magazine Extras”

PMA wheel bearings
McFarlane Aviation Products
– PFA supporter
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