Looks Can Deceive

Mechanics may think instructions are for idiots, but give em some anyway


Its every motorists nightmare, breaking down in an Audi in a rural town where the only mechanic knows only tractors, Fords and Chevys.

Surely, pilots reason, the same thing cant happen to airplanes. The technology is usually more familiar and the mechanics are more worldly. Besides, the FAA makes sure mechanics know how to fix airplanes, right?

If you believe that, youd better stick to a factory-standard 1978 Cessna 172.

The fact is that modifications done to airplanes through supplemental type certificates and even Form 337s can give mechanics headaches. Although the vast majority are straightforward installations that are intuitive to remove, service and replace, there are enough exceptions out there to give any prudent owner pause.

In investigations of accidents with mechanical causes, the NTSB has repeatedly found instances where installation appears straightforward but it is not, where maintenance manuals and STC information were not available to the mechanic, and where mechanics had access to the information but didnt ask for it or use it.

The most notorious case involved Sen. James Inhofes Grumman Tiger, which shed its prop in flight [Accident Probe, December 2000] long after a minor but common installation error. During the course of that investigation, the owner of the STC under which the Tigers Sensenich propeller was installed said hed seen hundreds of airplanes with identical installation errors over the years and estimated that 40 percent of all Tiger propellers are loose because of it.

While this flaw is now well-known in the Grumman owner community, thats not to say its well-known everywhere. Multiply that by the hundreds of products available to be installed hundreds of models of airplanes, and its clear that even the sharpest mechanic cant guess right all the time.

Look through the paperwork of a well-used airplane and its often surprising how much is missing. STCs may be logged, but the certificate and/or installation instructions missing. POH supplements? Forget it.

Many times this can be remedied by contacting the manufacturer or STC holder, or by getting copies of Form 337s from Oklahoma City. While it may work if you have the time and the manufacturer is still in business, it becomes a crap shoot if youre on a trip and the wrong thing decides to give out.

Legalities aside, any mechanic who is brought an airplane to fix will do what he can to fix it – especially if the owner/pilot is sitting on a couch at the FBO for his ride to be repaired. That motivation can turn even the most conscientious mechanic into a shadetree-type: Well, that looks about right.

As airplanes age, keeping track of the goodies that have been added gets more important. If your airplane features, say, an aftermarket 1956 Lear L-2 autopilot, you may run into a mechanic who says, Gee, Ive never seen one of these before.

The best time to take care of this problem is before it happens. Check your logs, W&B sheet and anything else you might have and determine what has been added to your airplane.

Get copies of all STCs, including installation instructions and maintenance manuals. If the manufacturer is out of business, try the type club for your aircraft.

Once youve assembled all of the paperwork, make three copies. Carry one set of copies in the airplane so you can provide it to the mechanic if you should break down away from home. Give one set to your mechanic. The shop may already have them somewhere, but keeping them all in a folder or bag with your tail number on it will cut down on the mechanics excuses for not using them. Keep the other set at home so that you can replace a set thats lost or damaged.

Study the FAAs Service Difficulty Reports, not only for your airplane, but also for the components installed on it. Learn which parts are straightforward and which are not. That way, when the airplane needs service youll be able to caution the mechanic that the job isnt as intuitive as he may think it is.

Being involved in the maintenance of your airplane wont just save you money, it will keep the mechanic on his toes and may just keep your airplane out of the trees.


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