This may seem waaaay basic, but it almost got me. Make certain the fuel caps are on completely and securely. Not long after earning my rating (in the R22), I flew to a nearby airport to give my first passenger rides. After landing, one of the admiring throng asked "whatsat hole?" Hole? WHAT HOLE? It was the open fuel tank, left side.
My heart skipped a few beats while thinking about the TR being in the path of the departing cap.
This ship had paint marks to line up indicating the cap was completely on, and I would swear I had COMPLETELY tightened it. I'll never know how it came off. The second piece of luck of the day was that the old tractor on the field used for cutting the grass had the EXACT same fuel cap. I moved the stock one to the left side, put the tractor cap on the right side, and as I flew back to base, I periodically reached outside with my right hand and felt that cap to be sure it was staying tight.
In retrospect, I wondered why the cap didn't have a safety chain so it couldn't go more than a few inches from the filler port.
