PSA: That intermittent fault on the 737-800 DME was a chafed wire behind the avionics bay panel

I was out at Oakland last Tuesday troubleshooting a DME that would cut out randomly on short final. Spent 3 hours checking antennas, swapping LRUs, even re-terminated the coax. Turned out to be a wire chafed against a bracket behind that panel near the E&E bay door. In my experience you have to physically trace every inch of those wire bundles before you start tossing parts at it. Anyone else ever chased a ghost fault that turned out to be a simple rub?

2 comments

2 Comments

matthewg635d ago

Five of those chafed wires in my last year alone at SEA.

mason2094d ago

Start by checking the connectors first, in my book. @matthewg63, five chafed wires in a year is a lot, but I've seen way more phantom faults that ended up being a loose pin or a corroded terminal, not a rub. At my last shop we had a DME that kept dropping lock, swapped everything, finally found a pin that was pushed back just enough to make intermittent contact at altitude. Chafed wires get all the glory, but I'd say 70% of my ghost faults have been at the connector level, not a wire rubbing a bracket. You really gotta look at the mating surfaces and the pin tension before you start pulling bundles apart.