Gyro part number
Admittedly, this actually happened to me. I was helping with some work on the Chinook crawling around in the nose compartment of the aircraft helping to look for a part number. I can’t exactly remember what magic black box we were looking at but I assume it was a gyro of some kind. I do remember being upside down with a tiny flashlight looking through a tiny mirror, desperately trying to locate a tiny number. Peeking around the corner I thought I finally had it. In my defense, the mirror reversed everything I was looking at and as we all know “objects in the mirror are closer than they appear”, LOL. For a second I thought “Ha! There it is!” yet the extreme shortness of the number quickly raised suspicion followed by the realization that all I was looking at was a label that said “TOP”.
I did find the actual number eventually but laughing at myself I thought that this is totally something Chuck would do.
Our classic is crankshaft serial numbers. “It’s 261111132” Those are timing marks
It’s similar to the people looking for a replacement cap number “710”.
Special mention to the serial Numbers on propellers : they are engraved on the back of the prop, so when the inspector wants to check it the number matches the one on the form-1 (8130-3 for the faa guys), it takes to remove the cone and the whole propeller from the plane.
So when the inspector finally signs of a valid arc for the plane, it has no prop installed, so is not very airworthy at that point…
Another classic from the world of technical support is the Eye-Dee-Ten-Tee error (that’s India-Delta-One-Zero-Tango).
Many years ago I was working on an older Mooney, doing something under the instrument panel in flight. I had the flight instructor flying and looking out. When finished I asked the FI where we were, he said he didn’t know he wasn’t paying attention. This is over flat crop land so everything looks the same. But we had an VOR station on our airfield, so I tuned it in and headed home. After too long a time, I said we’re somewhat lost, and started looking for landmarks. Finally found that we were flying away from home no towards. Then I figured out that the old VOR had the direction of flight on the bottom and not the top. So we did a 180 and headed home.