The Ins and Outs of Pre-buys

Dont buy a used Experimental aircraft without one (Part 1).


Bruce McGregor (left) looks on as Vic Syracuse inspects the engine installation of Bruce’s RV-12. The inspection for a pre-buy is almost the same as for an initial flight.

I was in the process of performing a pre-buy inspection on a high-priced RV-7 that the builder/owner had flown to my place. I think I actually felt a rise in my heart rate when I noticed that the horizontal stabilizer was not even properly bolted to the fuselage. I queried the owner about doing aerobatics and he said, “All the time!” I decided I wanted his guardian angel, and that episode, amongst others, keeps prompting me to help educate our readers with regards to pre-buy inspections. This month and next I’ll show you some insight on a methodical approach to buying an Amateur-Built airplane. I’ll even intersperse it with some stories that will make you want to laugh and cry at the same time.

Vic Syracuse inspects Bruce McGregor’s RV-12. It is really important to check the continuity of the control system, along with any known wear areas.

Why Do a Pre-buy?

It seems as though the continuing improvement in the economy has positively affected the aircraft market, and I’ve been busy doing pre-buys, especially on RV-10s. I want to share with you a sampling of the egregious things I am seeing for a couple of reasons.

First, as owners and operators of Amateur-Built aircraft, we don’t yet have a repository of information where we can all seek out service difficulty reports. While builders are usually aware of the numerous forums and type clubs, and know how to retrieve and share information on their particular model ( and the Matronics email lists are two such examples in the RV world), typical second owners who are not involved in building usually are unaware of these resources. If the buyer comes from the certified world, where they are used to having an A&P take care of their airplanes, they assume the A&P will do the same for their Amateur-Built aircraft. Now a licensed mechanic in lieu of the repairman certificate holder will perform the condition inspection. However, the mechanic may not be aware of the intricacies of homebuilt aircraft. As a member of the EAA Homebuilt Aircraft Council, I can tell you that we have identified such a resource as a high-priority item and are working to create one in the near future.

The tail section can usually be a good view into the rest of the airplane. Hopefully these crooked rivets and poor edge finishing did not continue throughout the rest of the project.

Second, in a past column I mentioned that I am really an advocate of a task-based Phase I, instead of the current hours-based Phase I that we are all familiar with. These have been pioneered and proven by some of the ELSA manufacturers, with the RV-12 being a great example. I am seeing a rapid rise in the appeal of the RV-10 to the non-builder market. When compared to the cost of any new certified four-place single-engine airplane, the RV-10 is about one-third the price and has almost the same capabilities. Consequently, a number of them are being sold immediately after the 40-hour Phase I completion. These aircraft are being presented to the new buyer with some very serious problems. I know I am seeing a small cross section of the available aircraft, but of late I have been looking at airplanes all over the USA, and I am a little concerned that the deficiencies are a widespread problem.

Personally, I think signing off an airplane with known problems borders on unethical, but a bigger concern is that someone might get hurt. In the case of an aircraft like the RV-10, we are talking about families, perhaps even unsuspecting families. Not right and not fair. I am a huge advocate of Experimental aviation, but the time and place for experimenting is without passengers. Here are a few examples and some ideas for a pre-buy checklist you might be able to use.

An inspection mirror and bright flashlight can be your friend and help you see critical areas for construction quality.

Missing Fuel Pressure

One recent and very interesting phone call I received was from a new owner who said his fuel pressure was indicating zero. Upon further inquiry, he couldn’t remember when he first noticed it was missing (yes, missing), as he had just spent about 8 hours in the airplane flying it back to its new home. In the process of sitting in the airplane to understand the glass cockpit, he configured the fuel pressure to be added to the display, where it now read zero. Since this was an injected engine, I had a high degree of confidence that his fuel pressure was not really zero, as we verified the engine ran just fine at full power. He proceeded to fly to my place, and upon arrival, I quickly removed the top cowl to verify the type of fuel pressure sender. It was clearly of the 12-volt variety, and a quick check with a voltmeter verified the presence of 5 volts. Yep, 5 volts! I then checked the engine monitoring system and verified it was in fact wired to the 5-volt supply instead of the 12-volt supply. A quick rewire to the 12-volt supply and it now displayed the proper fuel pressure. A phone call to the builder confirmed that it had never worked, so he had in fact deconfigured it from the display! In my wildest dreams I cannot imagine making even one flight in an aircraft with a fuel-injected engine without the fuel pressure readings, let alone flying for 40 hours and then signing it off. Fuel pressure is a checklist item in every injected engine I have flown. I think some of us are keeping our guardian angels working overtime!

The vertical fin cap on this RV-10 stuck out over 3/8 inch and acted as a fixed trim tab. The forces in cruise were so strong that the pilot’s leg would cramp after 20 minutes.

Bad Wiring

In another case, an aircraft that had been flying for 500 hours over a six-year period exhibited some pretty serious wiring issues. The GPS steering information never presented itself to the EFIS, and the VOR/ILS information was only partial and, in fact, appeared to be reversed. The right-wing strobe light came on when the nav light switch was activated. The builder/owner said he was aware of the erroneous indications and operations, and was frustrated with them, but had learned to fly the airplane just by looking at the moving map. Quite honestly, if I hadn’t thoroughly checked the avionics as I usually do during the pre-buy inspection, it could have been very confusing for the new owner.

The vertical fin on the RV-10 and most rear spars on wings require a castellated nut and cotter key due to the movement caused by flight loads. Far too many have an AN365 stop nut.

High Oil Temperature

The last example came from a conversation with a builder/owner regarding engine-operating temperatures. The comment was made that the engine temps never go into the “red.” As most of you know, with our new glass cockpits, we can configure the temp ranges anywhere we wish. I know some people who just keep changing the numbers until the alarms go away! When asked for actual numbers on oil temps, the reply was that it usually runs 205-239F in cruise. Yikes! I know redline is 240 for this particular Lycoming engine, but is there really a difference between 239 and 240? Take a look at the tolerance on the engine sensors and you might be surprised. I politely explained that it really wasn’t operating in the normal range for the majority of his type of aircraft out there, and that he might want to take a look at it. He graciously agreed, thankfully.

Here’s an example of a misdrilled and poorly attached vertical fin, coupled with two different sizes of nuts and four washers on one bolt alone. Max should be three, or else use a shorter bolt.

The Inspection Process

One of the first things I tell every prospective buyer is that they should not get emotionally attached to any particular aircraft until we have performed the pre-buy inspection, and that they should be prepared to be disappointed. Sometimes we hit it right on the first try, but about 50% of the aircraft I inspect fail to meet expectations. While there is usually a buyer for any aircraft out there, typical non-builders coming from the certified world want an airplane they can immediately hop into and go fly, so mechanical soundness, build quality, and avionics capabilities are paramount. Most aren’t looking for a project.

Let me explain my role in this process. I make it clear that I do not accept any commissions from the buyer or the seller. I am paid for the pre-buy. I will not represent any aircraft. I wish to be the objective third party who can ensure that the aircraft is safe and is as represented. When asked, I will advise on what current market values are as observed from the completed transactions I have been involved with. Rarely do they match the posted prices in the various sales publications or web sites. I am not here to drive the price up or down, as it really makes no difference to me. However, most airplanes end up getting pretty close to a condition inspection in the process, and all owners are very appreciative and work to rectify any discrepancies, even if the current sale should fall through.

Hidden underneath the “spacer” was actually a binocular shaped hole formed from two holes drilled too closely together.

So, let’s get started. Most of my questions begin with trying to understand who actually did the initial construction, how it has been maintained and operated, how it is equipped relevant to the buyer’s needs, and has there been any damage history. If we can get past the phone conversation, we usually then try to schedule a mutually convenient time for all parties to meet. Yes, sometimes a phone conversation will determine that the aircraft will not meet the needs of the buyer, and in a couple of cases the prospective buyer was even told that it wouldn’t pass if you were bringing Vic Syracuse. While that might be good for the current buyer, I hope another buyer is just as willing to seek out real expertise prior to purchase.

Look closely and you will see two open holes on the left side. They require AN4 bolts and have been found to be missing in far too many RVs.

What do I mean by real expertise, you ask? Don’t forget that these are Experimental aircraft and are mostly built by amateurs. Even with as many airplanes as I have personally built, I still consider myself an amateur and very much capable of making mistakes. I know, as I’ve seen me do them! Just because someone has built one aircraft doesn’t qualify him or her as an expert on inspecting one built by someone else. Who’s to say his/her aircraft is built correctly? Find someone who is really experienced on the specific type and has a good reputation. Good examples are DARs, EAA technical counselors, and qualified “repeat offenders”—builders who have completed more than one project. Most, but not all, of my experience is on the Van’s and Kitfox series of aircraft, so much of my focus in this series will be centric to those, but the inspection process is applicable to most other aircraft.

The bolt into the longeron did not meet the minimum edge distance required. Van’s provided an engineering fix that should be trouble free and much stronger.

The Checklist

I am going to separate the inspection checklist into four distinct categories: airframe, engine, avionics, and logbooks/documentation. I usually start with either the engine or airframe, depending upon the builder’s experience, as well as what I’ve already gleaned from the initial phone conversation. A good place to start is at the tail. This is where most builders begin construction and develop skills used throughout the rest of the construction process. In the case of metal airplanes, it is easy to see misdrilled or improperly placed holes and overdriven rivets. On composite airplanes look for poor or sloppy layups. For tube and fabric aircraft, welding skills are really put to the test around the tight tubes and clusters in this area. Fabric covering skills are also put to the test here, with all of the sharp bends around small tubes. It is also a view into the builder’s application of best practices such as the use of torque seal on bolts and jam nuts.

Loose jam nuts on control rods are a too-common occurrence, even on airplanes that have been flying for a while. They should be tightened during final assembly and then marked with torque seal.

Review the Plans

Be sure to familiarize yourself with the aircraft plans. As an example, some aircraft in the Van’s series require a washer in the vertical stabilizer attachment on one side to offset the vertical fin. Some of the vertical fins, like on the RV-10, require the use of a castellated bolt and nut on the forward fin attach, much like the rear spar, due to the movement of these structures imposed by flight loads. About half of the ones I inspect are improperly secured. Loose jam nuts on the rod end bearings are another common finding and, in fact, have even generated a service bulletin by Van’s Aircraft. Over time the loose jam nuts will cause cracking of the flight control spars if not caught. So far my record stands at finding 12 loose jam nuts on a single airplane! Torque seal can be your friend here. If there’s no torque seal, better get the wrench out.

Don’t forget to inspect the airplane either before or after it is disassembled. This misalignment can cause cooling problems with the engine, as well as reduce power.

Check the Controls

While at the tail, it is a good time to check for complete and full control movement. Here again, I am amazed at the number of airplanes that have problems in three particular areas relative to flight controls:

  • Control surfaces that bind prior to reaching full deflection.
  • Controls that do not even reach full deflection due to improper rigging or interference, of which improperly installed autopilot servos are the biggest contributors.
  • Reversed trim, which comes to light in about 30% of the inspections for new aircraft. However, I inspected one aircraft that had been flying reversed for seven years, and the pilot stated he had just become used to it. I promptly rewired it for him on the spot, and he was very appreciative.

In a couple of cases, I actually had to argue with the builders long enough that I questioned out loud if they were really pilots. One builder tried to convince me that the stabilator trim on an RV-12 worked in reverse because it was a stabilator. Huh?

In the case of a Storm 320E, which happened to be the first kit completed in the U.S., I was uncomfortable with the five degrees of up elevator travel. Enough experience building model airplanes and real airplanes told me that five degrees just didn’t seem like enough, especially if needed to break a bad flare in this nosegear aircraft. We both agreed that a call to the manufacturer was in order, and sure enough, a more reasonable 15 degrees of up elevator was specified, requiring an adjustment of the stabilator pitch and antiservo mechanism.

Wherever a bolt is subject to rotation, it is best to use a castellated nut and cotter key, especially here at the rudder cable attach points.


For taildraggers, pay particular attention to the tailwheel. It’s usually fairly easy to lift it off the ground to perform a thorough inspection and should be done regularly. Check for loose or worn wheel bearings, improper spring tension, proper lubrication, and sound structural integrity where it attaches to the fuselage. I’ve seen many center-locking tailwheels fail prematurely due to improper lubrication.

Moving Forward

From the tail, inspections usually progress to the tail cone and/or baggage area. In the past one could expect to find only ELTs and strobe power supplies behind the baggage bulkhead. It is much more complicated today. In well-equipped airplanes remote avionics such as ADS-B receivers and transponders are the norm, and sometimes they even include air conditioners and complicated battery backup systems. On top of the complexity, they are installed in areas that don’t normally receive inspections during the course of a year, and can also have an adverse impact upon the aircraft CG. It is typical for me to find loose jam nuts here, especially on the autopilot servo linkage, as well as missing safety wire or lock washers on the servo bolts. It is also important to check that the autopilot linkage does not allow an over-center position when the controls are moved throughout their full deflection. While back there, take a close look at the static system to insure it is routed properly to avoid any potential water collection.

ELTs need to be checked for proper operation (during the first 5 minutes after the hour), and the battery needs to be checked for replacement dates. The required annual logbook entry for ELT checks is the most often missed entry that I see. I see a fair number of inoperative ELTs, and in one case during a condition inspection, the ELT was discovered to be completely missing! By the way, this was on an airplane that was sold after 25 hours to a non-builder. The new owner had been unknowingly flying her newly built RV-9A all year without an operative ELT. Not cool.

Be careful to ensure that autopilot servos will not travel over center when the controls are fully deflected. One aircraft had intermittent jamming due to this condition.

Inspecting the Wings

Next, I move on to the wings. There are a couple of critical areas here, not the least of which is their attachment to the fuselage. After all, it’s not really an airplane without wings, so we might want them to stay attached! Here again, it is important to understand the designer’s intentions and directions. In the case of the RV series, so many people have forgotten to install four bolts into a particular wingroot spar location that Van’s has recognized the need for a service bulletin. And just as in the forward attach point of the RV-10 vertical stabilizer, the rear spars require the use of a drilled bolt and castellated nut due to the movement on the rear spar caused by flight loads. About 20% of the aircraft I inspect erroneously make use of fiber lock nuts here. I have come to the conclusion that by the time builders mount the wings at the airport, they are no longer referring to the plans, either due to overconfidence at that part of the journey or due to the fact that the plans were left at home during the move. Airplanes such as the RV-12 and Kitfox series, with removable wings, need to be closely inspected for proper security of the attachment hardware.

Most of you already know this, but just in case, do remember that the red nav light goes on the left wing, and the green one goes on the right wing. Yes, I inspected one airplane that had them reversed!

Flight control freedom of movement, along with the proper amount of deflection, needs to be verified. The flaps also need to be checked for proper operation, and in the case of electric flaps on the Van’s series, there is a service bulletin detailing the requirement to drill and safety wire the flap actuating motor, another often-missed item. While underneath the wings look through the inspection panels to check for corrosion, especially on airplanes that have been repainted. Sometimes the stripper can run down inside the wings and cause problems, as can Alodine when not appropriately rinsed.

While under the wing it is easy to check the pitot tube for proper mounting, and for proper operation in the case of heated pitot tubes. While having someone apply aircraft power with the pitot heat turned on, you can usually feel the tube begin to warm up. Don’t forget to turn it off quickly. I also check the landing gear while I’m already squatted on the floor for the wings. Most homebuilts, and even some certified airplanes such as the Grummans, Cirrus, and Columbias, make use of a castering nosewheel for ground steering, requiring attention in a couple of areas. Brake wear is usually high in the initial hours as the pilot gets used to the free-castering nosewheel, and the breakout force of the nosewheel needs to be properly set according to the manufacturer’s specifications. If left unchecked, brake pad wear can get to the point that it allows the actuator puck to deploy far enough out that the o-ring seal is broken, followed by loss of brake fluid and braking ability, the results of which can lead to bad consequences. It can take some discipline by the operator to regularly remove tight-fitting wheelpants in order to carefully inspect the brakes. I highly recommend this to new owners.

This pitch servo is mounted without the use of locknuts or safety wire.

Missing Cotter Keys

I’ll leave you with another sad-but-true experience with one RV-7. I noticed that neither wheel had a cotter key installed in the axle nuts. When I pointed it out the builder stated, and I quote, “We really cranked them down and have already performed our taxi tests. They aren’t going anywhere!” Yikes! Better get some new bearings on order soon.

Next time we’ll continue with the wings, engine, and paperwork.



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