Airframe and Powerplant

Prepurchase Prep

September 1, 1998

What you do before the purchase will mean a lot afterward

There are already enough hard-and-fast rules in aviation, but here's one to which adherence is crucial — never buy an airplane without a comprehensive prepurchase inspection. Even the simplest of airplanes is a complicated mechanical beast that should have all its systems in good working order. Buying an airplane with a lame engine, corrosion-riddled airframe, arthritic avionics, and problem-plagued systems is an invitation to fiscal disaster, even if it is bargain priced. The much-used adage applies here: Pay now or pay later.

A thorough prepurchase inspection is your safety valve. But before you so much as start looking at candidates in the flesh, you should endeavor to learn as much as you can about the particular model and its quirks. Join a type club. There are few better ways to become immersed in the breed than joining the type club. Do so with the aim of learning the common trouble areas and successful fixes, not just to shop for all the neat goodies you can lavish upon your still-unbought airplane. Usually, you will get a magazine from the type club as well as references for shops and mechanics familiar with the model. Many type organizations also have Web sites and e-mail lists — a form of noninteractive chat room — that are an absolute gold mine of information for the new owner. Sign on to one of these and watch your e-mail for priceless nuggets of owner information. (A listing of type clubs is available at

As your shopping progresses and you narrow the field, keep a few basic concepts in mind. Try to buy the best example of the model that you can afford. Buying a basket case is a sure way to lose money unless you plan on keeping the airplane for a long, long time. Also, don't stretch your finances so tight when buying that you can't afford a few maintenance glitches in the first year, and an annual inspection that could cost 10 percent of the purchase price. Many new owners report expensive first annuals, which is caused by your own mechanic's starting fresh and putting things right "his way." Also, resist the urge to buy the first airplane that you inspect. It's OK if you come back to it, but make sure you play the field enough to learn the typical condition of the make and model you're considering. Yet again, use the services of the type clubs: Many have regional fly-ins that can be offer a wealth of information and good advice. (At the event, you might also find the airplane that you're looking for.)

An ideal prepurchase inspection is actually as rigorous as an annual. Many experienced buyers recommend going the whole annual route during the prebuy, preferably using a mechanic who has never seen the airplane before. You can use the airplane's usual A&P for the inspection, but you'd have to trust him implicitly and be present during the inspection for it to be fully meaningful. The side effect of a prepurchase-as-annual is downtime — a complex airplane could spend a week in the shop, something the seller might not countenance if the normal annual has just been completed. Most important, you want the annual structured in such a way that certain stopping points are well understood.

You don't want the shop to do everything on the annual checklist if you find a soft cylinder, cracked case, or evidence of corrosion early on. So another tactic is to target certain critical parts of the airplane for an early inspection — a basic engine and airframe look-see to determine whether the airplane makes the first cut. Then, if all looks good, continue into the more detailed inspections. Plan on at least a half day for a simple airplane and a full day for a complex single — call it $200 for a Cessna Skyhawk and $500 for a Beech Bonanza. Budget a bit for consumables.

Paper primer

Your first step in buying the airplane should be to visit with the owner and take a leisurely stroll through both the airframe and the logbooks. (Buying an airplane with missing logs can be tremendously risky, particularly if the absent pages are in the recent past. In this case, it's up to you to prove total engine time and compliance with airworthiness directives (ADs) and service bulletins (SBs). If you undertake such a task, make sure that the asking price is reduced accordingly.)

Look over the logs carefully and keep a running set of notes. Be alert for premature engine changes and overhauls, frequent repair notes — such as an alternator belt that is replaced often — and subtle references that could spell damage history. A careful perusal of the logs will probably disclose any damage history, but you need to be sure that the appropriate inspections are carried out on the airplane, too. Ideally, the logs will be in good order, and the history of the airplane should be evident.

Particularly for older airplanes, the ebb and flow of engines, avionics, and paint can make for fascinating reading. Check that the pitot static system and transponder are current for IFR and that the ELT battery is within guidelines. Jot down the serial numbers of the major components — including airframe, engine, prop, mags, and governor — and make sure that they match what's on the airplane.

Compliance with ADs and SBs is a bit stickier. You can have your own listing of ADs printed, but the SB listing is a bit harder to obtain; again, seek the advice of the type clubs on which SBs are important and which are not. And while SBs — even those marked, menacingly, mandatory by the part manufacturer — are not considered compulsory by the FAA for Part 91 operators, you should see some evidence that the "good sense" SBs have been complied with on your candidate. Note, too, that many ADs have alternate means of compliance, some including modifications that either reduce or eliminate the repetitive nature of the inspection. Look for airplanes that have had the mods done to remove the recurring inspections. After all, minimal maintenance will eventually come home to roost — just make sure that you don't own the nest when it does.

Go fly

Before spending the money to have a shop look over the airplane, fly it. (There are precious few good reasons for buying an airplane you haven't flown.) Ask the owner to fly the airplane on a local flight. Your job is thus — see how he flies the airplane. Is he smooth and careful — though the excessively fussy types are no better for the airplane than the brash — and does he manage the engine well? Does he take the time to preflight or just hop in and go? You can tell a lot about an owner's philosophy by watching him fly.

While you're up there, ask for some stick time. Does the airplane feel the same as others of the same type? Are the controls free and smooth? A sloppy airplane is usually in need of rigging or control-system work. Does it make book performance? (Take along your handheld GPS and do a simple two-way speed run to rough-calibrate the airspeed indicator.) Take off your headset and listen for any unusual creaks, groans, rattles, and air leaks. Check to see that all the radios work — use each com and VHF nav radio, including the ILS if you can — and that the engine instrumentation performs normally. Here's where you look for unusually high or low engine temperatures and pressures. If you do your homework, you'll know what is normal for any given make and model. Take a turbo model to altitude to determine if it can make rated manifold pressure up to its critical altitude.

When you conclude the flight, check the belly of the airplane for oil and other excrement, and peek inside the cowling for new leaks and seeps. Understand, also, that it's difficult to keep some engines from weeping oil, particularly older, high-time models — so a bit of seepage is not necessarily a deal killer.

Engine matters

Because the powerplant is often the most expensive and complicated single piece on the airplane, it makes sense to start there on the prepurchase journey. You should ascertain the total time of the engine and the time since major overhaul or replacement with a factory reman. Double-check the claimed figures — mathematical errors have been known to happen — and understand that the potential for making it to the manufacturer's stated time between overhaul (TBO) is greatly dependent on not only frequency of use and piloting technique, but also the quality of the overhaul. A service-limits "dip and strip" job will be much less likely to arrive at TBO unscathed.

At a minimum, have a compression test performed, remove and cut open the oil filter (ask also to see recent oil analyses), and do a borescope inspection. This last item will help you to determine the basic condition of the cylinders — often, the place you're most likely to find trouble — and alert you to short-term mayhem. A skilled inspector can tell you a lot about how the engine's been run and its life expectancy with a simple borescope job. Then again, use this data point as just one of many. A past-TBO engine, no matter how clean inside, is still a past-TBO engine, and you'd better have the budget to replace it at any time.

Also be on the lookout for late-specification components. An air-melt crankshaft on a Continental, for example, will add a minimum of $2,500 to the overhaul. Early cylinder castings are generally more prone to cracking than later styles. It's usually a good sign when the cylinders were replaced at the last overhaul; conversely, old jugs that have an unknown number of cycles are usually not a good bet for long life, and you should value the airplane accordingly.

Spend much of your early inspection time focusing on the engine and its accessories. How long since the prop was overhauled? Are the fuel system components freshly overhauled — at least as new as the engine overhaul — or is their status undecipherable? Are the hoses less than five years old? Plan to replace anything more than 10 years old immediately. Are the mags and harnesses relatively new and, if not, are all ADs complied with? Check the exhaust system for leaks and, on turbocharged airplanes, plan to spend some time checking the turbo, controller, and associated plumbing. (Again, it can't be overstressed that you need to be talking to a mechanic or shop that knows the type of airplane intimately. The more complex the airplane, the more crucial this requirement.)

Airframe and systems

By far, the most important part of inspecting the airframe is to determine the presence and extent of corrosion. These days, with the fleet age nearing 30 years, corrosion is the number-one killer, way beyond mere old age and availability of parts. Look into the logs and see where the airplane has lived. While a dry-country airplane is not guaranteed to be corrosion-free, you are at least facing less of a battle than with one left outdoors in a salty environment. Open a few inspection panels early in the prepurchase inspection to make sure it's safe to continue; if it is, plan on opening most or all of them during the inspection proper.

For retractable-gear airplanes, perform a gear swing to confirm that the alignment is correct and that all of the gear subsystems are working properly. Check the condition of the wheels, tires, and brakes. Understand that rebushing or shimming an out-of-alignment gear system can be expensive. High total time is but one indicator of gear wear, so ask if the airplane has been based at or flown into rough fields recently.

Move systematically through each subsystem. Are the brake lines in good condition and the reservoir full? How old are the fuel bladders — if installed — and is there any evidence of fuel leakage? How old is the battery, and what is the condition of the battery box?

Put up or shut up

At the end of the inspection you should have a very good idea of the airplane's condition and the quality of recent maintenance. At this point it's usually time to come to an agreement on the price and any other details of the purchase. (AOPA's escrow, aircraft-valuation, and title-search services can be a big help here.) But a few other items are worth mentioning. Try to buy an airplane that has been flown regularly in the recent past. Nothing hurts an airplane more than lack of use. Also try to find one that's outfitted as you'd like it — the return on investment for major upgrades such as paint, interior, avionics, and a powerplant swap is quite poor in the near term. Finally, remember that if at any time you or your shop finds something that raises an eyebrow or calls into question the basic airworthiness of the airplane — walk away. With few exceptions, this will not be the only airplane in town. After all, buying smart is the best way to control the cost of flying.

Links to all Web sites referenced in this issue can be found on AOPA Online ( E-mail the author at [email protected].