Airworthiness Question

[Flyin' South]

Is a C-172 still airworthy if on the preflight inspection the pilot finds a missing screw on the engine cowling, yet the cowling appears and feels secure?

 

[Deftone45075]

We got ramped once and the Fed. made an issue of a missing Zeuss fastener.

 

[avbug]

Strictly in terms of liability, yes. The aircraft does not meet it's type design criteria. However, for a specific aircraft, you may very well find that the maintenance publications will permit a certain number of fasteners to be missing, for a given component. This is a case where you cannot simply make a generalization.

Airworthiness, as defined by the FAA, means that the aircraft meets approved data (type design, as ammended by STC, AD, etc, approved maintenance publications). It also means that the equipment is safe for operation, which will include adherence to standard industry operating practices and proceedures. This will include publications such as AC 43.13.

If you can find a publication that generally states a missing fastener is okay, and can tie it to your airplane, you're golden legally...unless publications exist for your airplane that dictate otherwise.

A missing screw may not seem to be a big deal, and in many cases, it's not. However, I can tell you about circumstances I've had or been involved with that appeared normal, but weren't. One case became very public last year. When I first saw it, it was a small spot of dirt under a wing, which turned out to be a small crack after stripping the wing and doing dye penetrant checks. Later it turned out to be a completely cracked wing...and a few years later, the wing left the airplane in flight on national television. Very small things may be indicators of big things.

Take a missing fastener, for example. Just a screw. But why is is missing? Worn tinnerman, or excessive vibration? Crack adjacent to the screw hole or fastener? Missing nutplate? I've seen what appeared to be a smoking rivet that upon inspection was found to be a completely failed member beneath the surface.

During an annual on a light twin once, I investigated a pilot complaint that the controls seemed a "little heavy." He thought that there might be a worn pulley or perhaps just a hinge that needed lubrication. I found the ELT out of it's mount and the coax intertwined between the up and down elevator cables, some five or six times...only a matter of time existed before the elevator would have become stuck in flight (most likely). Small things indicating bigger things.

What about a fastener that shows even with the fibrelock nut? Is it legal, or airworthy? Most instructors probably wouldn't know that at least one thread must be protruding beyond the fastener to be legally airworthy. They preflight it, but don't know the standards of airworthiness. The fact that the fastener is there is all good and well, but is it airworthy? No.

One missing screw on a cowling probably won't dent your day. But why not just put another screw there and call it good?