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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 .

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 .

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
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