Had a weird ground loop hum in the cockpit I finally tracked down

Last month I was working on a Cessna 172 and there was this nasty 60 cycle hum in the audio panel. Spent a whole afternoon chasing antenna grounds and checking the comm radio. Turns out it was a loose bonding strap between the engine mount and the airframe, just a few strands of copper still touching. Has anyone else had a ground issue that was hiding somewhere totally random like that?

3 comments

3 Comments

the_wendy1mo ago

Flew a plane for a week with a hum I thought was just "character" before finding it was a loose screw on the audio panel ground. Wasted more time chasing phantom gremlins than actually fixing the thing.

vera_johnson91mo ago

Wait, did you say you found it on the engine mount bonding strap? I would've never thought to look there. I used to just assume grounding hums were always in the radio or the antenna cables, figured that was the only place they lived. But after chasing a bad ground in a plane that turned out to be a rusty screw on the instrument panel frame, I totally changed my mind. Now I check every single metal-to-metal connection, even the ones that look totally fine. It's crazy how such a tiny thing can make such a big noise.

-1

miller.emery1mo ago

totally fine" lol yeah @vera_johnson9 that phrase gets me every time. Had a Cessna that drove me nuts for two weeks with a static burst every time I hit the flaps. Everyone told me it was the antenna ground, so I rewired that thing three times. Finally my buddy just starts poking around with a multimeter while I flip switches and he finds the bonding strap on the flap motor mount barely touching. Tightened it one quarter turn, static gone instantly. Made me realize I gotta treat every single connection like it's a suspect, no matter how solid it looks. Like you said, it's wild how something so tiny can wreck your whole audio.