I remember a flight I did years ago in a Piper Arrow with an instructor. Early in the flight, I noticed that the elevator trim wheel, which was always a bit stiff, seemed harded to move than usual. It seemed to get worse during the flight. On an ILS approach at the end of the flight, I found it impossible to trim the plane. The instructor wanted to fiddle with the trim wheel to see if he could make it better. I had a strong instinct that we should leave it alone and refused to let him mess with it. The plane was flyable, it was just annoying to have to keep forward pressure on the yoke. After landing, we told the mechanic and he investigated. He later showed me that the trim cable had slipped over time, allowing a turnbuckle to bind against a pulley. Had we continued to force the trim back and forth, the plastic pulley could have split, letting the cable go slack and allowing the trim tab to move however it wanted. I’m not sure what would have happened, but I’m glad we didn’t try to use trial and error to diagnose the problem in the air.

Trim authority can be critical to aircraft control, especially in larger aircraft. I understand the pressure on commercial pilots to continue to their destination, but I would have landed immediately if I was the PIC on that flight. It’s much safer to diagnose problems on the ground, regardless of how upset the passengers might get or how late the freight might be.

John