Originally Posted by
Maoraigh1
Play safe. Return and check on ground. Anything different in an aircraft I'm familiar with is worth investigating.
If far from home or alternate airfield, return.
A loose starter warning light wire, flapping against earths, caused oil pressure drops on an electric meter with no wiring near that loose wire. But the combined pressure/temperature gauge showed a steady, normal, temp.
That is what I did. As soon as I saw the needle wiggle I told the student to turn around and head back to the airport which was about 4 miles behind us. After the turn the oil pressure needle gave another wiggle and settled still in the green but noticeably lower. At that point I made a mayday call and told the tower we were going to land straight in downwind rather than join the circuit. By the time we were on short final the oil pressure was indicating zero psi so I shut down the engine and we made an uneventful landing keeping up enough speed we were able to coast to a stop off the runway on the taxiway next to the flying school.
After confirming no oil pressure with a shop gauge mounted directly to the engine the oil filter was removed and had a significant amount of metal inside, The engine was sent to an engine shop and it was determined that a tooth on the oil drive gear had broken off. This caused the gear to skip which eventually broke all the other teeth so the engine oil pump was no longer driven. As the engine was near TBO it was decided to just overhaul it rather than do a full tear down inspection and repair.
As a very new instructor I occasionally flew with an elderly gentleman who's family insisted he fly with a safety pilot. He was the poster child for been there done that and was a fount of knowledge. I asked him for pointers and one of them was where he made a point of suddenly covering the engine instrument cluster with a map and asking me where each needle was. My lame "UMM in the green" was met with a sigh. He told exactly what each gauge was reading without looking and noted that by doing that he was more likely to catch the often subtle changes in gauge readings that are the first indication something bad is happening. It was directly because of his advice that I stared monitoring engine gauges in a systematic manner and meant I caught the failing oil pump in time to return to the airport with the engine still running,