Whistling in the Dark
Sometimes because of my A&P certificate, I am asked for my opinion about the airworthiness of an aircraft. This happened recently when a young instructor asked me to look at a Schweizer 300 helicopter he was scheduled to fly with a student. He showed me what appeared to be cracks around the bolts that attach the struts to the tailboom. He wisely recognized that should this bolt lug fail, the boom would certainly leave the aircraft, and he would have a very bad (though short) day!
Sometimes in these situations, I have a level of comfort with the part or machine and thus, easily offer an opinion; other times, I just don’t know. Though I’m a certificated mechanic, I don’t have any real experience working on Schweizer helicopters. So my default mode in these situations is this: if I don’t know, I don’t go – and I advise my questioner (who obviously doesn’t know either, or he wouldn’t have asked) to stay on the ground until we do know. We can’t be killed by an aircraft we don’t fly.
“Not knowing” is a common place for humans to find themselves; in spite of our best efforts, we just can’t know everything. So what do we do when we face this “unknown” chasm before us?
First, we gather new information: we call the experts, perhaps the mechanic who worked on the aircraft last, the mechanic who regularly maintains it, the pilot who last flew it, or the owner who has a history with the machine. We also consult the FARs, the service manual, service bulletins, and other supporting data that might provide clues. In other words, we research the issue.
Only after this crucial step is honored do we get our hands dirty. The unwritten methodology in maintenance is to start with the simple and inexpensive and work toward the complex and expensive. This might involve ever-more extensive disassembly or throwing increasingly expensive parts at the problem.
Start with a careful inspection of the suspect part. This might just begin with your fingernail and a good light for a crack like the one we had. Get a bright flashlight, though — and a mirror, if necessary. Lighting is critical here; a dark hangar won’t do, and surprisingly, a brightly-lit ramp might be just as bad because it’s often too bright and offers no contrast. A simple magnifying glass is often the perfect tool, or you might need some NDT (non-destructive testing) methodology like dye penetrant to “get deeper” into the problem. If that doesn’t solve the uncertainty to your satisfaction, you might have to remove more parts, inspection panels, or cowlings; paint might have to be stripped.
After a cursory inspection of the cracks, several phone calls were made. The mechanic who regularly cares for the machine offered to come look at it. After carefully inspecting it, he assured us that the paint was cracked because there are rubber shock grommets around the boom’s attach bolts, and they had been painted over some months ago; needless to say, the natural action of those grommets easily cracked the paint over time. So, what appeared to be potentially life-threatening cracks turned out to be “normal” and the little helicopter was good for flight.
But how would you know unless you asked? We simply don’t know what we don’t know. Would it have been worth it to fly the aircraft…and just hope that it was OK? I call that “whistling in the dark….”