hall.ruby•2d agoMost Upvoted

Had an altimeter go haywire on a Cessna 172 yesterday afternoon

I was doing a routine pitot-static check on a 1978 Cessna 172 out at KAPA around 4 PM. Everything was going fine until I got to the altimeter and it was reading 200 feet off when it should have been dead on. I pulled the thing apart and found a spider web inside the case blocking the static port. Never seen that before in 6 years of doing this. Has anyone else ever found weird debris inside an instrument that threw off your readings?

2 comments

2 Comments

hugo_jones21d ago

A guy at the hangar last month was telling me about a similar thing on a Piper Archer, except he found a dead moth blocking the static port on the back of the altimeter. Said the thing was reading damn near 500 feet off at pattern altitude, which would've been a real problem on a cloudy day. I always give the static ports a quick blast of compressed air before buttoning things back up now, especially if the plane's been sitting for a while.

richardfox1d ago

500 feet off at pattern altitude is a pretty minor error in the grand scheme of things, you'd barely notice it unless you were shooting a tight instrument approach. Honestly, blasting compressed air at ports is probably doing more harm than good if you end up pushing a bunch of dirt and debris deeper into the static system.