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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


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
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