Prepurchase Inspections – Jacobson

The Prepurchase Inspection

With the average age of the general aviation fleet at 30 year, the importance of doing a comprehensive pre-purchase inspection before you buy is greater than ever before. In this article, an aircraft purchasing expert discusses the ins and outs of a getting good pre-purchase, and offers a detailed inspection checklist.

By Brian Jacobson| March 1, 1998

The airplane purchase process is a long and difficult one for most people, especially first-time airplane buyers. That’s because there is a great deal of hard work involved. If you want to be sure that the airplane is worth the purchase price and is in the condition that has been described to you, several essential steps must be taken prior to consummating the deal

In everyday life, we try to make everything we do as simple and easy as possible. When it comes to buying an airplane, however, there’s no easy way out. If you handle your airplane purchase like you might an automobile, you are leaving yourself wide open for problems.

Now more than ever

 It was different back in the 1970s when light planes were being produced in large numbers, and most of the ones being sold on the used market had very low airframe times. You could be fairly certain that an airplane with less than 1,000 hours on the airframe and no damage history would not kick you in the wallet too hard if something went wrong after the purchase was completed. Back then, a prepurchase inspection generally consisted of a compression check, a quick AD search, and a cursory inspection of the airframe.

Today, it’s an entirely different story. The average age of the general aviation fleet is 30 years, and some of the airplanes on the market have over 10,000 hours in service. Not only are lightplane prices much higher (most have appreciated handsomely in recent years), but the price of replacement parts for them has gone completely out of sight. To the prospective buyer, this means serious sticker shock if anything significant goes wrong after the purchase. When mechanical problems turn up and the bills for unscheduled repairs start coming in, often during the first year after purchase, it isn’t long before the new owner starts questioning whether aircraft ownership is such a good idea after all.

That’s why a prepurchase inspection is so vital…and why it shouldn’t be just a quick once-over, but a thorough look at the airframe, engine, systems, instruments and avionics. The more complex the airplane, the more time and energy must be put into a prepurchase inspection.

Who’re you gonna call?

As soon as you’ve decided what kind of airplane you want to buy, you’d be wise to start giving serious thought to how your prepurchase inspection will be conducted, and by whom. Some mechanics refuse to do “prepurchase” inspections. They claim that they don’t want the liability if something goes wrong after the airplane changes hands, especially if it involves something they didn’t look at. Consequently, you should be prepared to provide your mechanic with a detailed list of things you want done during the inspection. At the end of this article is a checklist of items that I recommend including as part of every prepurchase inspection.

Different mechanics have different views of how a prepurchase inspection should be done. Some mechanics look at the very basics: they’ll do a compression check, verify that AD compliance is up-to-date, and briefly look over the airframe for current damage or the signs of previous damage. Other mechanics will insist on doing what almost amounts to an annual inspection before they are satisfied. Not many mechanics have the knowledge or equipment to check the instruments and avionics. That’s why it’s so crucial that whomever you choose to do the work understand precisely what you want, and advise you if he cannot accommodate you.

By asking your mechanic do a thorough job on the prepurchase, you’ll know that the airplane is safe to fly, and be reasonably confident that nothing major is going to cause you any grief in the foreseeable future. A cursory inspection, or none at all, can leave you open to all sorts of problems that are preventable.

I am amazed at the number of people today who buy a used airplane without doing any prepurchase inspection at all. I get calls from them all the time, generally after they have had their airplanes for a while and things are not going smoothly. The ugliest cases involve airplanes that were represented as “no damage history” but subsequently turn out to have been damaged. Most of those callers are worried whether the value of their aircraft has been diminished by the just-revealed damage history or the repair work necessary to make the aircraft legally airworthy.

Sometimes, a buyer can sue to recover the amount of diminished value if it can be proved that the seller knew there was damage history and covered it up. But the cost of repair work is almost never recoverable. That’s why you do a prepurchase inspection. Once the bill of sale is signed, the aircraft is yours, along with any problems it has. Most purchase and sale agreements state explicitly that there is no warranty of any kind offered with the sale.

Airplanes aren’t automobiles

Years ago the owner of a Cherokee 180 asked me to sell his airplane. It was a low-time airframe, though it desperately needed a paint job. An acquaintance at the airport called me as soon as he saw my ad and said he had just decided to buy an airplane of that type. He asked that I take it to Mac, a mechanic at another airport whom I also used to maintain my own personal airplane. If Mac passed the airplane, he told me, he would buy it.

Mac was a very thorough mechanic, and it didn’t take him long to find that the compression on two cylinders was low. He put a borescope in each of the cylinders and told me that he thought there were broken rings because it looked as if the cylinder walls were scored.

I called the owner and told him what Mac had found. He replied that he didn’t believe there was anything wrong, but to be sure he’d take the airplane to his regular mechanic and have it checked. A week later I got a call from him saying his mechanic had given the engine a clean bill of health.

I decided to call the owner’s mechanic myself, and we had a little chat. The mechanic told me he’d used an automotive compression gauge and tested the cylinders’ compression. The automotive tester is placed into a spark plug hole, and the engine is rotated using the starter. The gauge records the highest pressure that is trapped in the cylinder during the test, but that doesn’t tell much about the cylinder’s health.

There’s a big difference between an automotive compression tester and the differential compression test that is standard procedure for aircraft engines. Using the differential pressure method, the mechanic pumps 80 PSI of pressure into a cylinder through a calibrated orifice with the piston at top-dead-center, and measures how much of the pressure the cylinder retains. Seventy PSI (“70/80”) or more is considered excellent compression. A measurement of 60/80 or less will mean more testing, but there’s a significant likelihood that the cylinder will have to be pulled and repaired.

Needless to say, after my conversation with the owner’s mechanic, I dropped the airplane from my list of airplanes for sale. Not too long afterwards, I heard that the engine on the Cherokee quit on a cross-country flight. The pilot/owner had to make an off-airport landing that resulted in substantial damage but, fortunately, no injuries.

Airplanes are not automobiles and cannot be treated like them. They must be maintained by people who know what they are doing and what the standards are for airworthiness. It is vital that the mechanic you use for your prepurchase inspection be thoroughly versed on the particular model of airplane you are buying. Your life and the health of your bank account could depend on it.

Those dreaded ADs

Research into the aircraft’s Airworthiness Directive (AD) compliance is a very important part of any prepurchase inspection. ADs can be very expensive to comply with, but non-compliance with an AD can render an airplane unairworthy. Few potential buyers are in a position to check AD compliance themselves, and some mechanics don’t do a thorough job of it either. So, when you discuss your prepurchase inspection with the mechanic you select, make sure he or she understands that you want a thorough AD search done.

One problem that occurs occasionally is that a mechanic will make an entry in a log that he has complied with a particular AD without giving any details. If the AD has several methods of compliance, that can lead to problems later. For example, an AD on a landing gear side brace may require an inspection every 500 hours and replacement of the brace at 3,000 hours. If the mechanic replaced the side brace because it was found to be faulty but the logbook stated only that the AD was complied with, the brace would probably be replaced again much sooner than necessary. Worse, the replaced side brace might be an improved part that was no longer subject to the AD, but without a complete explanation in the logbook a new owner and his mechanic might have a difficult time determining whether or not the recurring provisions of the AD still applied. When considering the purchase of an airplane, the availability of detailed maintenance records are a big plus.

More stuff to check

If you are buying a retractable gear airplane, make sure your mechanic puts the airplane on jacks and does a thorough evaluation of the landing gear system. Each strut, trunion, brace, linkage and actuator should be checked for excessive play and wear. The gear should fit snugly into its wells and complete the extension and retraction cycles within the cycle times specified in the service manual. Gear doors should fit properly, and their hinges should be free from excessive wear. Some landing gear systems can be more difficult than others to maintain, but any retractable system that is worn or neglected will be expensive to repair.

Part of the prepurchase inspection is insuring that the instruments and avionics all work. Unfortunately, most mechanics are not well-versed on avionics, and many airports lack a shop with the necessary knowledge or test equipment to check them. If a radio shop is available on the field, make sure you include it in your prepurchase inspection plans. It generally will take an avionics technician no more than an hour to check out the radios and instruments. If you can’t take the plane to an avionics shop, another method is to fly the airplane after the mechanical portion of the inspection is completed and check out the radios and instruments yourself. If you’re not familiar with the equipment, make sure you find someone who is to make the checks. Sophisticated equipment such as autopilots, flight directors, weather radars and GPS receivers can have many features that should be tested, but if you’ve never used that model before, you probably won’t know how to check it.

Cost considerations

What should a prepurchase inspection cost? It varies depending on the type and complexity of airplane you are looking to buy, what the mechanic finds wrong with it, and how deeply you want him to get involved. Four years ago I paid $500 for the prepurchase inspection on my Piper Arrow, and it was worth every penny. The shop that did the work was outstanding, and when they were done I knew exactly what was wrong with the airplane. The discrepancy list added up to nearly $3,000 in repairs, including two cylinders that had small cracks around the spark plug bosses. After some negotiations with the owner, we completed the deal and I flew the airplane home.

Many shops will not quote a flat rate for a prepurchase inspection. It is usually done on a time-and-materials basis. If the shop rate is $50/hour and the inspection takes 8 hours of labor, you are looking at $400 plus whatever materials are needed. Parts cost is usually minimal, but should include an oil filter (because the mechanic should cut the installed one open to inspect it for metal), and possibly other materials such as gaskets, cleaning solvents, and a quart of oil to replace what was in the filter.

If the annual inspection is coming up in the next three months I try to turn the prepurchase inspection into an annual. It’s not always possible, and the cooperation of the seller is required because the airplane is tied up longer than it would be for a prepurchase inspection. Not only does that give your mechanic a better look at the airplane, but you don’t have to stop flying it three months later for an annual.

If you are in the market for an airplane, be certain that you take all the mandatory steps that are required before taking delivery. The prepurchase inspection is vital to a successful sale no matter who you are buying the airplane from and what the apparent condition of the airplane is. Skip it, and your new airplane could turn into disastrous money pit.

Prepurchase Inspection Checklist

Here’s a list of prepurchase inspection items. A knowledgeable person other than the mechanic can do some of the cosmetic items, but any discrepancies that are seen should be pointed out to the inspecting mechanic for his appraisal.

Before Inspection

Run engine until warm.

Check operation of starter, vacuum pump, alternator, magnetos, propeller (if constant speed) and other accessories.


General Condition Inspection

Check for dings, dents, and cracks that must be repaired because of their nature.

Check for current damage.

Check for obvious signs of previous damage.

Open several inspection plates. Check for internal corrosion.

Check control cables for correct tension.

Check for fuel leaks on upper and lower wing and fuselage surfaces.

Check controls (including trim tabs, flaps, and cowl flaps) for alignment, rigging, full travel, freedom of movement and security.

Inspect cabin and exterior for signs of water leakage and damage.

Check cowling for fit and security. Note any repair work needed for cracks.

Check cabin and baggage doors for correct fit.

Check cabin and baggage doors for hinge wear.

Check tires and brakes for security and wear.

Check glass for cracks, crazing, and scratches.

Check all antennas for correct installation and security.

Check pitot heat. Check pitot tube and static sources for obstructions.

Check fuel vents for obstructions

Check fuel caps for tightness and seal

Check fuel placards for correct type of fuel and quantity.

Check all external and internal lights for operation.

Check seat belts and harnesses (if installed) for wear.

Check seats for correct movement and that proper stops are installed.

Check that compass card is installed.

Check condition of plastic interior trim.

Check oxygen bottle (if installed) for quantity and leaks.

Check condition of oxygen masks (if system is installed).

Check that weight and balance, equipment list, and airworthiness certificate are present and current.

Check for known problems common to the type of airplane.

Jack aircraft. Inspect the belly for possible damage or excessive exhaust residue. Cycle the landing gear and check for proper operation and security. Check operation of emergency gear extension system.

Check the ELT for operation and current battery.

Check battery box for corrosion. Check battery for proper charge.

Check under instrument panel for proper avionics and equipment wiring.

Check condition of instrument filter.

Check circuit breaker panel for correct markings.


Check for oil leaks.

Check for evidence of exhaust leaks.

Check muffler for evidence of cracks or wear.

Check compression using differential method.

Check alternator belt for security and wear.

Take oil sample and send to lab.

Cut oil filter open and check for unusual metal or other contamination.

Check security of all accessories. Check them for case cracks.

Check cylinders for cracks in known locations and around spark plug bosses.

Check engine case for cracks.

Check oil breather system for obstructions.

Check condition of ignition harness.

Check engine mount for cracking and lord mount wear.

Check condition of firewall.

Check condition of electrical wiring forward of the firewall and as it goes through to the cabin.

Check propeller for nicks and/or leaks.

Check operation of all mechanical controls.

Check ignition switch for proper operation.


Research all AD notes.

Check service bulletin compliance. Make recommendation for complying with significant ones that have not been done.

Check logbooks for damage history.

Check annual inspection entry for proper signoff.

Check for IFR recertification.

Compare engine, airframe, and propeller serial numbers with those in logbooks.

Verify engine and propeller times since major overhaul.

Check age of bladder fuel tanks (if installed).

After Completing Inspection

Install cowling. Check all engine controls and cowl flaps for proper operation.

Run engine. Check for oil leaks after installation of new filter.

Avionics (If Radio Shop Is On Field)

Check operation of all installed equipment for tolerances and proper operating characteristics.


This article used with permission from AvWeb

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