That wiring diagram from the 90s almost killed a test flight last week

I was double checking an old Cessna 172's pitot static system and found out the factory wiring diagram had the ground loop pinned wrong on the connector. The plane had been flying like that for 20 years, no one caught it. I only found it because I was chasing a weird airspeed reading and pulled the pinout sheet from the manufacturer's archive. Turns out a revision in 2003 changed the pinout but nobody updated the old birds. We had to rewire three planes on the line after I flagged it. Where do you guys keep your wiring revisions? I swear half our hangar still uses photocopies from the 80s.

2 comments

2 Comments

kelly3856d ago

Old wiring diagrams are fine as long as nobody's messing with them. I've got a whole binder of 80s era pinouts for our fleet and we've never had an issue because we don't touch the harnesses unless something breaks. Changing the revision just because a factory update came out is more likely to cause problems than it solves, especially if you're working on planes that have been flying 30 years without incident. Your ground loop issue sounds like a connector corrosion thing or a bad crimp, not a diagram problem. If the plane flew fine for 20 years with the "wrong" pin, maybe the factory diagram wasn't wrong. Maybe your reference was the wrong revision. I store all my wiring info in a beat up three ring binder and nobody's died yet.

briancarter6d ago

Old schematic binders work fine until someone retires and the new guy can't read them.