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I finally had an APU fire warning on a 737 last Thursday night shift
Been doing avionics for 8 years now, mostly on Airbus stuff. But last Thursday in Atlanta I got a call about a 737 with an APU fire warning on the ground. No actual fire, just the warning. My lead said it's probably a bad detector loop. I thought he was wrong, figured it was a control card issue. Pulled the APU panel and tested the loops with my meter. Sure enough, one loop showed open circuit resistance way out of spec. Replaced just that detector loop assembly. Cleared the warning on the second test. Lead just nodded and walked off. Felt good but I still think the control cards on these older 737s are garbage. Has anyone else had a false APU fire warning turn out to be something weird like a chafed wire instead of the detector?
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jake9864mo ago
No way you had a lead who actually let you pull the APU panel and test loops before arguing about it for 20 minutes. Thats wild. Usually mine would just throw a parts cannon at it and make me swap the whole APU control unit first because maintenance control says the computer knows better than a meter. Chafed wires are definitely a thing too, had a 757 once where a zip tie had sawed through a bundle right behind the fire handle and gave us a warning every time we hit turbulence. Your call on the detector loop being open was solid work though.
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dixon.iris4mo ago
@jake986 nailed it with that chafed wire story, seen that exact thing on a different bird too.
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