Turbine Pilot Special Section: Before You Buy, Prebuy

Turboprop prepurchase inspection

October 1, 2009

A prepurchase inspection is always a challenge, whether the airplane is a J–3 Cub or a Boeing 727. But a turboprop, with its combination of jet engine(s) mated to propeller(s), plus its many systems, makes for one of the most difficult. Here’s why, based on my 32 years of inspecting aircraft for buyers.

‘AOPA Pilot’, Turbine Edition, OCTOBER 2009

Table of Contents

D-JET Dawn
Moving to turbine power
Up and coming
The next airplane
Brazilian breakaway
Before you buy, prebuy

Paperwork

I carefully read each page of the airplane’s logbooks, and the older the airplane the more pages there are—and the more attention must be paid. If the paperwork (or worse, lack of it) for prior repairs, installations, and modifications is not right, I start an intrusive inspection. One deal-killer here is a gap in maintenance history, or missing logbooks. Remember that the owner must keep FAA forms 337 for any airframe alterations, but some facilities that perform major repairs do not have to issue a Form 337.

I’m not fooled by fancy computer printouts designed to identify maintenance and safety issues. These printouts make it easy to find airworthiness directives, service bulletins, and the status of any inspections. But they don’t know about an airplane’s damage history or other unusual events. This is where scrutiny of the logbooks pays off. It may not seem right to have to spend more on repairs than the asking price of an airplane, but that can be the reality. It’s either pay now or pay later.

The power of a good prebuy is that it can be your last opportunity to get free maintenance. After I have spent some time with the airplane, find it is worth buying, and the troubleshooting has begun (on the seller’s nickel), then I can put a price on the defects. And I usually find defects exceeding 10 times my service fee.

Preflight

—sometimes, enough to kill the deal.

First off, I get the owner to top the fuel tanks the night before, then ask him to place the airplane in a dry spot so I can check for leaks when I get there.

Then I open the cowls and look for signs of leaks in the engine compartment. I also write down fluid levels, and identify any stains or rivets with broken paint—which I mark to see if they work loose or turn in flight. I also tug on the wings, the tail, and the doors, looking for play and noises, and examine the windows, which should be done in the sunlight so that scratches show up better.

Next come ground runs, operating one engine at a time. Here, I write down all the engine instrument readings. Then come propeller feather (or negative-torque sensor) checks. I’ll also go outside and check the deice boots by running my hand over them while they’re inflated (on the side of the static engine, of course, in the case of twins). Taxiing is for checking the brakes, making 180-degree turns, looking for gyro precession, and noting the behavior of the magnetic compass and heading indicator. A VOT check and GPS reception check should also be made.

Airwork

When it’s time to fly, I bring my aircraft-specific prebuy checklist with me. This checklist emphasizes those defects that I usually find on this make and model of airplane. The takeoff and landing numbers from the airplane flight manual are on the checklist, but I also identify runway markers (for example, runway lights and/or runway intersections) so that I can verify the distance when the wheels leave ground, and how much distance is used for landing.

Before takeoff I flip every switch, checking to see what works and what doesn’t. Then it’s a climb to the airplane’s maximum operating altitude to check engine performance. During the climb, I check the rates of climb passing various altitudes, and record true airspeeds, engine temperatures, and fuel flows. This gives me an idea of how well the engines are performing compared to POH numbers. I’ll also check all the avionics, and even ask ATC for altitude readouts to check the encoder’s accuracy.

Remember, this is not a pilot training mission, so I’m not the pilot in command. I’m only paying attention to my prebuy-specific checklist. Besides, if something bad happens, I don’t want to be responsible. I ask the seller to supply a pilot on his insurance for these evaluation flights, and then make sure the pilot understands not to exceed any operating limitations.

While I may not be pilot in command, I do fly the airplane. I’ll make performance runs, check the cabin pressurization and heat, and then spend some time in the aft cabin, nosing around for vibrations, sounds, and pressure leaks.

Back in the cockpit, I’ll slow the airplane, then cycle the flaps and landing gear, looking for the proper speeds for warning-horn activation. Pulling some Gs and getting a feel for the controls also is important. When it comes time for a descent, I want to see it made near redline airspeeds so I can look for oil canning, signs of flutter, and pitch-trim irregularities.

The avionics get special attention, especially the autopilot. I let it do most of the flying—after all, that’s the pilot you’re buying. Coupled autopilot approaches are a must, and full ILSs are needed to check all components. Same with full RNAV approaches, to see if the GPS receiver(s) are performing up to par.

For the ILSs, I note the crossing altitudes at the outer and middle markers, and verify that what I see on the altimeters matches the published crossing or glideslope-intercept altitudes.

Landing

I videotape the landings, and make sure that I note the reverse and beta mode functions. Runway permitting, it helps to make the approach a little fast so that I can have the extra time to study the gauges and make sure the power lever gates, detents, and linkages all work as they should.

After the buy

Let’s say the customer decides to buy the airplane. A good idea is to digitize the records, because some day the buyer will sell it. This will increase the chances of future buyers coming to see the airplane.

My last prebuy was a Hawker 125-700 with 11,000 hours on it. After putting all 7,000 papers (log entries, 8130s, yellow tags, invoices, prior maintenance bills, 337s, and other documents) on a DVD, I added the video of the flight test. To top it off I organized the system troubles into folders, for quick reference. Then I put everything on an 8-GB USB flash drive to carry on a key chain. It knocks the socks off educated buyers.

Don Sebastian has been president of Aviation Consulting Services Inc. since 1980. Contact him at prebuy@gmail.com.