What do I need to have done on a pre-purchase inspection?
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Pre-Purchase Inspections
Created by Bob Steward, A&P-IA
Minor editing by Mike Rellihan for 19/23/24 applicability.
Mechanical Difficulty: (Not that you’d do your own inspection…)
There are as many different ideas on the proper scope and depth of a pre-purchase inspection as there are buyers. What makes that interesting is the expectations of those buyers, and how those expectations change after owning a plane for eleven months, and having gone through the dreaded “first annual”.
When is a better time to discover the true condition of the plane; during the purchase process, or after the money has changed hands and the plane has flown away? This is the reason I always suggest that a purchaser do a thorough pre-buy; and do all that is reasonable to identify things that will later bite him in the wallet. What that means is a full Annual Inspection by the checklist in the factory maintenance manual; for example, nine pages for the 19/23/24.
“But it just had a fresh annual last month, and has flown nearly no hours since then.”
Perhaps; but who did the inspection, and did you get a copy of the signed, dated list of discrepancies? To what extent was the Inspector motivated to find everything that might be ‘wrong’ with the plane?
Most planes sell because the owner is moving on. Sometimes it is to larger or smaller aircraft, but often it is away from aviation altogether. So what did they tell the mechanic that performed the last Annual? Probably something along the lines of: “I’ve got it listed in T-A-P, so don’t spend any money on it that you don’t have to.” That is a pretty sobering thought, when you know that you are going to take your family and friends up in your new plane, just as soon as you can get it home.
Another factor that enters the discussion is that an “Annual Inspection” is just that; an INSPECTION. As in LOOK at it. No repairs or service work are part of the actual Inspection. And while its true that the basic oil, filter, fluid levels, and mag timing checks are regularly performed in conjunction with the Inspection, that is just a convenience for the owner. Since the plane is in the shop, they have it opened up, and most planes haven’t had any service work since LAST year, it costs less to service it in conjunction with the Inspection.
So if it has just been inspected, and no actual work was done to repair or improve the plane, just what did you get? Probably just the bare minimum that the FAA requires, for the plane to be legally operated. Certainly nothing that says there won’t be any catastrophic failures, or even minor items wearing or breaking, on the very next flight. The plane was just “looked at”. Maybe sort of a ‘super pre-flight’. I’ve read so many tales of woe and expense after purchasing a plane; and yet it seems that new buyers never learn, and the same mistakes are repeated again and again.
Let’s go over some items that really ought to be checked, during the pre-buy inspection on your intended purchase.
Paperwork
As strange as it may seem, the FAA is far more focused on the paperwork than they are on the actual components. The reason for this is that if the paperwork is correct, then the physical components can be manipulated to create “Airworthiness”. However, if the paperwork is incorrect, then one cannot make the plane “Airworthy” because the records that support the airworthiness are incomplete or inaccurate. The FAA takes this to the point that the DATA PLATE is the component they are most interested in; the rest of the airplane or engine just consists of parts which can be replaced as needed.
One must have the ‘AR(R)OW’ paperwork for flight, and one must have an Airworthiness Certificate to confirm that the aircraft in question was EVER in a condition to hold US Certification. Many planes were built and shipped overseas without ever having US paperwork, such as the ones that went directly to Canada that often are brought back to the US later. The price, especially considering the current exchange rates, may be very attractive, but one is left to PROVE to the FAA that the plane conforms to its Type Design, and is therefore eligible to have an airworthiness certificate issued.
Logs are an important part of the paperwork. It is quite common to see planes for sale with some or all of the logs missing. This is a big red flag for the novice buyer. WHY are the logs missing? It could be that they were truly lost or destroyed. It’s possible that the plane was a repossession, or transferred in an estate at some time, and the logs were not available to the new owner. Or, a more nefarious possibility is that they were intentionally kept back to avoid the documenting of repairs from some unreported accident! Perhaps there were even substandard repairs that included the use of undocumented parts or unapproved repair techniques. Lost logs require an even higher level of due diligence on the part of the inspector and purchaser. Buying a plane with absent or incomplete logs will also result in very large expense to an A&P-IA to recreate the missing documentation. Every AD will have to be researched, including major disassembly as required. If past paperwork can’t be found on things like engine and prop, they may have to be overhauled in order to establish their ‘legal condition’. Airframe total time will have to be estimated ad newly-established based on any existing FAA or repair records, and recurring AD times will be based on the fresh inspections and airframe (plus engine and prop) time.
Prop
Props have a TBO, just like engines. When is it due for an Overhaul? Just consult the manufacturer’s data for the prop in question. Most fixed-pitch props are due for OH at engine OH, or at any time that they have wear or damage that exceeds the prop manufacturer’s field dressing limits. Props are a “Class 1” appliance in FAA-speak, and that means that they SHOULD have their own log. Most older planes do not, and this then makes it more difficult to establish the history of that prop (especially if there is NO log). Models such as the McCauley prop used on the 70’s production Tiger have AD-mandated inspections every 200 hours. Without a dedicated prop log, where are those entries kept? Usually in the Engine or Airframe log, but what if a prop is bought used? Did you get the airframe log entries showing past compliance with the AD, and an accurate Total Time In Service? Better obtain a $5 prop log and transfer the available history to it, and begin logging inspections and maintenance from here forward.
Engine
Sellers are very fond of speaking highly of the good running of the engine, even though it’s very near or at TBO. The implication, if not outright spoken statement, is that TBO is just a ‘suggestion’; and since THIS engine is running so well, has such fine compression, and uses negligible oil between changes, that it’s going to reach TBO (and even go well beyond).
Of course, this is total hogwash. No one can predict the future accurately by relying solely on past events. The manufacturer (Lycoming) has established a TBO based on field experience. What Lycoming has actually said is that the criteria for determining what the REAL TBO for a particular engine should be is in Lycoming SI 1009AR, and is based on 12 calendar years, OR 2000 hours, WHICHEVER COMES FIRST. Note that different engine models and variants can have different TBOs.
Now, how do you feel about that 30 year old engine with “mid-time”? It’s already 250% past its factory recommended TBO! Busting the TBO by a few percent is one thing; by 2-1/2 times is another. How much steel have you seen that is corrosion-free after 30 years, in or outside of an engine? Especially if the usage has been low and infrequent?
Airframe
The single largest issue can probably be summed up in one word: Corrosion. As the fleet ages and time takes its toll on our light alloy airframes, oxidation is the number one problem that the fleet faces. The factory engineers never expected that we’d be flying significant portions of the fleet 45 years after initial production. They built the planes to last 10-15 years, and then expected that we’d scrap them and buy new ones. If aviation products didn’t go up at over twice the rate of inflation, perhaps that would be the case. A new $30,000 Sundowner? Sure, where do I mail the check?
I recently inspected two Grumman AA-5x series planes with corrosion in the center spar. Not some light surface corrosion that might leave little pits in the spar tube, but full-blown inter-granular corrosion that was raising bumps on the spar tube. Neither plane was a “Florida” plane, but both needed a replacement center spar. The corrosion was severe enough on both planes that you have to ask WHEN in the last 20+ years of Annual Inspections was this overlooked, since it was quite obvious that it hadn’t just popped up in the last few months. Fortunately there are now products such as ACF-50 and Corrosion-X that can prevent corrosion, and halt light cases. The Beech Aero Club also has a few Beech kits that will enable members to repair outboard spar corrosion damage, though the process isn’t cheap.
The Inspection Process
The inspection should be performed on the plane after the owner and the prospective purchaser have met, flown the plane, and negotiated a price for sale in its stated condition. The buyer should ask for, and the seller should supply, a complete list of every known squawk. This along with the Total Time of the airframe, engine and prop, the list of installed equipment, and an accounting of any life-limited components comprise the documentation of the stated condition. At this point, the price has been agreed to, the buyer wants to purchase the plane, and the seller is willing to sell and warrant the plane to be as represented.
The Pre-Purchase Inspection is now scheduled, with the intent of determining if the plane meets the stated condition by the seller. The purpose is not to pick the airplane to pieces and scare away the buyer, or to find thousands of dollars worth of work the seller should pay for; rather it is to establish the true condition of the plane for comparison with the previously prepared squawk list. It is even possible (and desirable) to do a PPI on a WRECKED plane. Again, the purpose is to bring to light the true condition of the plane, so that both parties are aware and accept the current condition as the basis for the sale.
It is quite common to surprise the owner with items that are worn, cracked, corroded, etc. And the seller and buyer make adjustments in the price to account for them, or the seller has them repaired to everyone’s satisfaction, in order to bring the plane back to the previously stated condition, upon which the sale price was negotiated. Or the buyer accepts the known shortcomings, or walks away instead. Even if the buyer winds up being out-of-pocket for a share of the PPI costs, that is far better than learning about corroded spars or fuselage frames at the next Annual Inspection, having already bought the plane.
Specific Inspection Targets for the 19/23/24/76/77 Aircraft (Mike Rellihan)
PROP
Verify that the prop is the correct make and model for the application, based on the Type Certificate Data Sheet (available for download from BAC or the FAA).
Make a close examination of the prop, using a magnifying glass.
Check the spinner AND backplate for the correct application (if possible), and for cracks; and for past unapproved repairs (patches and stop-drilling).
Verify prop log entries, including Total Time and Since Major Overhaul status. If the prop looks quite worn, or is beyond the recommended TBO (whether Fixed or Constant-Speed), an overhaul is probably in the cards.
Verify whether the Hartzell prop hub is still subject to the 2006 AD requiring recurring 50-hour Eddy Current Inspections; or whether the hub has been replaced with an A-suffix or B-suffix hub. If the no-suffix hub is still is service, the next prop overhaul will include an added cost of at least $3,000 for the new hub.
NOTE: This does not apply to fixed-pitch props on the 19/23 models; nor to the 3-blade McCauley upgrade sometimes seen on the Sierras.
ENGINE
Verify that the engine is the correct make, model, and variant for the application, based on the Type Certificate Data Sheet (available for download from BAC or the FAA).
Verify engine log entries, including Total Time and Since Major Overhaul status.
Check the status of all critical accessories, including the magnetos, carburetor or fuel injection, starter, generator or alternator, vacuum pump, and prop governor (if so equipped). For example, if the correct engine came with a generator, but the inspected engine has an alternator, do the aircraft records reflect the proper paperwork entries for the conversion? If the vacuum pump has more than 1,000 hours on it, it is overdue for replacement.
Check the TSO tags on all hoses for assembly dates. This means brake lines, hydraulic gear lines, and the fuel hose at the wing root (inside the plane). Also all the hoses firewall-forward at the engine. No tags? More than ten to fifteen years old? Then the hoses are not airworthy. Tagged Teflon hoses have no published life limit in their original application, but are seldom found on our planes.
Perform a standard inspection for such things as ignition harness and spark plug condition, chafing standoffs, and duct condition. Control cables, cabin air mechanisms, induction air box and filter, alternate air valve, exhaust system, and cabin heat shroud should all be examined. All the controls should work freely, including the air and heat controls.
Examine any oil leaks. If oil is coming from accessories or the nose seal, it can probably be reasonably repaired. If it is coming from the parting line of the case, from a crack in the case, from case through-bolts, or from the cylinders, it will probably require a major repair expense.
Obtain oil analysis results and an oil filter media examination, to check for aberrations. The oil analysis will show only major departure from norms, in the absence of a trend history.
The Models A23 and A23A came with the Continental IO346 engine. Only about 540 of these installations were made, between 1965 and 1968. While a good engine, it was used in very few other airframes, and none of any volume. As a result, there are no new or aftermarket cases, cranks, and cams available for this engine (new cylinders and accessories remain available). If a major component is needed during an overhaul, it will likely take some time and money to find it. If you buy a plane so equipped, you should begin to collect these parts whenever you run across them. Few shops can set up the fuel pump pressure and injection system properly; as long as it is working right, that won’t matter. If it is dying on roll-out, or under other circumstances such as cold starts or during taxi, that’s a different story. The engine life (TBO) is much shorter on the Continental, compared to the Lycoming engines (1,500 versus the Lycoming’s 2,000 hours). There are a handful of recommended engine shops that work on them.
AIRFRAME
Corrosion is a BIG deal. Any mention or indication of corrosion makes me very nervous. True light surface corrosion, usually in the form of Filiform (little ‘worm tracks’ under the paint), is usually no big deal if not widespread and caught early. ‘Patch corrosion’, forming under larger areas of bubbled paint, is of much more concern, as it implies a wider range of issues (serious contamination under the paint, corrosion extruding from inside parts, lack of any previous airframe corrosion treatment, etc.).
Please make absolutely certain that the technician has thoroughly inspected all areas of the wing spars for corrosion. Ditto for the rudder and vertical stabilizer, the Stabilator, under the interior side panels, under the glareshield below the windshield (in the instrument panel area), and under the floorboards everywhere the old black air ducts touch anything. Some of these areas will require either disassembly, or the use of a Borescope, or both. Common flight surface corrosion areas include the vertical stabilizer and rudder, the Stabilator and tab, the outboard wing spars, and the flaps.
A battery box corrosion problem is pretty common. A new battery box is very expensive. It will have to be removed for proper repair, to prevent recurrence. Once fixed, the best prevention is to replace the battery with a sealed AGM battery from Concord or Gill (Aviation Consumer recommends Concord). Much more about this is available on the BAC website (corrosion and batteries).
Cabin air ducts should be checked to see whether they are still original. All the originals were rubber-impregnated fabric with piano wire. The fabric held moisture as it aged, and the piano wire rusted badly. If it touched the aluminum anywhere, it will have caused corrosion. Problem areas are anywhere under the floor skin and in the side walls (and overhead) where the ducts run; under the center spar splice, if the ducts touch there; and any brake, fuel, or hydraulic lines touched by the ducts.
The interior plastic trim panels should be removed, the old yellow insulation removed, and the areas inspected for corrosion due to window leakage. This includes the areas under the windshield, and the kick panels. The cowl cheek air vent inlets often have broken boxes or clogged plenum drains. Radio stack cooling ducts are often bad or missing, or spitting water due to clogged drains.
Hinges and hinge wires should be checked. Problem areas are the door hinges and stab tab hinges.
Windshield and windows need to be examined for cracks and visibility. They should be firmly bonded to the airframe with Polysulphide adhesive sealant; not just screwed in and caulked with silicone or RTV. In many cases a light press will reveal acrylic that is disbanded and leaking.
Wiring. Intercom, and antenna connections should be checked for condition, neatness, and type of wire. Unshielded single-wire jack connections will be an endless source of noise complaints and ghost-chasing expense. Ditto for a rats nest of added non-aircraft wiring and fuse-holders under the panel. Original wiring should have faint labeling that identifies the wire grade and size, along with the circuit identification. Old or added junk wiring, and abandoned wiring, cables, and antennas, will create a future expense.
Instruments and avionics should be checked for status and performance. Make sure that EVERY function gets checked IN FLIGHT. This includes all autopilot functions, if so equipped. Monitor for noise in the headsets during these tests. Make note of the age and capability of the instruments and avionics. KX170B (and later) radios are still solid performers, and are repairable by most shops (for a price). The KT76 and KT76A transponders are money pits, as are most ADF receivers. A solid-state transponder is a plus, as is an IFR-approved panel-mount GPS, newer radios, and a newer intercom.
Landing gear components should be checked for condition, adjustment, and lubrication. Problem areas are the nose gear pivot and linkages (and associated rudder trim); knee pins and bushings (all gear); gear cushion age and condition; and the rigging of the retract systems. The gear pump must not shut off before the nose hear downlock engages fully; and the gear must free-fall without any restriction, during emergency extension. An auxiliary nose gear downlock switch installed on the retracts is a plus.
GENERAL UPGRADE AND REPAIR COMMENTS
Keep in mind that virtually anything you accept for future repair will likely surprise you by what it costs later. Even low-end interior refurbishment (carpets, seat covers, side panels) will almost certainly exceed $2,000, even if you can do much of the R&R work. Low-end paint will start around $6,000 for a complete strip and repaint.
Slide-in replacement digital radios will run about $1,500 and up. A complete radio stack upgrade will probably start around $10,000 and climb from there. Installing even a simple autopilot will probably start around $5,000, unless you stick with the completely serviceable Brittain units originally used in these planes.
Most Loran and GPS panel-mounts, if VFR-only, won’t be upgradeable to IFR; and won’t have the capabilities of even low-end modern hand-helds. Don’t pay any extra for them. If the plane has an IFR-approved panel-mount GPS, be sure to find out whether it is enroute only, enroute and terminal only, or enroute, terminal, and non-precision approach certified. Limited installations are typically not upgradeable. WAAS capability brings precision GPS approaches; very worthwhile but still rather rare. Garmin 430s and 530s are expected to be upgradeable to WAAS (for a price).
SPECIAL CONSIDERATIONS FOR LOW-TIME OLD AIRCRAFT
The engine will almost certainly require overhaul due to corrosion; this may be true even if it was properly ‘pickled’ for storage, unless it was re-examined and re-pickled at the specified intervals. Both of these are highly unlikely; it is not likely to have been pickled per the manufacturer’s instructions, much less re-pickled. Not only is this aspect expensive, but there may be many more parts within the engine that are found to be completely unserviceable due to corrosion; things like the crank, rods, pushrods, and accessory case gears (and shafts) may all be found pitted, in addition to the normally-expected things like cylinders, cams, lifters, etc.
All the engine accessories (mags, etc.) almost surely have bad seals, corrosion in key places, etc. This includes the carburetor. Virtually every single ball bearing on the plane (wheels, alternator, gyros, whatever) will probably have some degree of pitting from recurring condensation that has formed, sat, (and even occasionally dried out), in the same place, time after time, because nothing has moved.
The exhaust system is probably rusted in places such as welds, even if it was made of stainless steel, and the engine mount itself would need a close inspection. Normally, with regular use, an oil vapor film protects it from most corrosion. The mount cushions would be bad, as would be nearly anything else made of rubber in the plane (not just the engine compartment and brake system hoses). All these parts require regular usage to retain their plasticity and to prevent hose liner cracking. Ten years is even beyond the allowable shelf life of most non-Teflon hose tubing, before it is assembled into a hose and placed in service. Once placed in service, the standard materials in hoses, fuel pumps, etc. will not tolerate extended disuse without later disintegration (after having been allowed to dry out or stiffen). This effect can even occur on an engine-driven diaphragm fuel pump that is only a few months old, if it is removed from an engine for something like a top overhaul, and left so that the diaphragms are exposed to air on the bench for a couple of weeks.
Particularly if the plane has been tied down outside, corrosion could also be a major airframe issue. Stationary aircraft develop corrosion in places that are normally drained and dried through in-flight operation. This can happen due to condensation even if the plane is kept hangared. The in-flight combination of aircraft attitude, lowered humidity at altitude, vibration and friction, airflow, and forced drainage all keep an airframe dried out. Hidden corrosion can range from spar caps (hard to see all of them), to a corrosion ring inside the fuel tanks, where it can’t readily be seen in these planes. The vertical stabilizer is often a problem area for this as well, in areas that are very difficult to see in a normal inspection; ditto for the Stabilator, tab, and flaps.
If there are any trim or autopilot servos, they would have to be checked. A coupled aileron servo can’t be very easily checked for ‘hunting’ on the ground. It will probably ‘hunt’ in flight due to a servo commutator oxide film, even if it passes a left-right check on a roll selector knob.
It is almost a certainty that all the hydraulics will need at least an overhaul, if not replacement (master cylinders, brake hoses, wheel brake cylinders, brake disks and pads).
The landing gear cushion biscuits have almost surely all hardened up. The tires and tubes are probably all bad. There is probably corrosion inside the wheel bearings, and inside the wheel halves themselves.
Assuming a fixed-pitch prop, there could be hidden corrosion not found until the prop is removed from the crank, and the blade reparability is probably unknown. If the Lycoming crank nose AD has not been complied with, there may be unairworthy pitting by now in the nose of the crank.
Presumably the avionics could be tested, but with the results unlikely to be very good. Antenna connections have probably deteriorated. Bearings in things like gauge needle movements and gyros have probably been affected. Electrolytic capacitors in things like gauge circuits and radios will have changed values or gone open.
The instrument air hoses and gauge hoses for oil, fuel, and fuel vent are probably all stiff as boards. A piece (or pieces) may come off on the first engine start, or may just wait to haunt you well down the road. Instrument air fitting screens may at first help protect the main gyro instruments (if they are there); maybe the first failure will just be the vacuum pump. Oddly enough, while vibration is often viewed as the enemy in our aircraft, it just as often goes a long way toward keeping things dry, lubricated, and flexible. When large aircraft first transitioned to jet engines, using the same avionics installed in their piston forebears, vibrators had to be installed in the instrument panels to keep the gauges working right. Regular flight accomplishes this in our planes.