TIL a bad ground wire can make a 737's TCAS go haywire

I was working a night shift at a maintenance hangar in Phoenix, doing a routine transponder check on a 737. Everything looked fine on the bench, but when I power cycled the TCAS, it started throwing false traffic alerts non-stop. Turns out a ground screw in the rack had corrosion so bad it was barely making contact. I spent 45 minutes chasing ghosts before I pulled the rack and found it. Replaced the screw and cleaned the terminal, and the system came right back. Has anyone else run into weird avionics glitches from a simple ground fault?

4 comments

4 Comments

wood.faith3d ago

I used to think avionics gremlins were always some complex software bug until I had a similar issue on a CRJ200 where the weather radar would randomly stop working. Turned out a ground stud in the avionics bay was loose by maybe a quarter turn. Tightened it down and everything came back perfect. The corrosion buildup on that 737 ground screw sounds exactly like what I've seen on older wire lugs where moisture gets trapped. It's wild how something so simple can make you chase your tail for an hour lol.

robin6283d ago

Oh man, I've been THERE. The worst part is you spend all that time pulling your hair out over the corrosion when a simple 1/4 turn and some dielectric grease would've fixed it in 5 minutes. I always tell guys to CHECK the grounding points first before doing ANYTHING else with the avionics. A loose or corroded ground will make you chase ghosts all day long. I keep a little tube of anti-corrosion compound in my bag just for this exact scenario. It's literally the cheapest and easiest fix you can make, but it saves you HOURS of troubleshooting.

murphy.aaron3d ago

Dielectric grease is definitely the move for the connector pins, but just a heads up, dielectric grease actually doesn't conduct electricity. It works by sealing out moisture and preventing corrosion, not by making a better electrical connection. So slapping it on the mating surfaces themselves can actually mess with the contact. You wanna put a thin coat on the outside of the connector housing and the back of the wire lugs, not between the actual metal-to-metal contact points. A lot of guys glaze that stuff on the pins and wonder why their connection gets flaky later.

wilson.joseph3d ago

Stick with a tiny brush or a q-tip and apply it just to the backside of the lugs like you said. I've seen guys glob it on the pins and then wonder why their ohmmeter shows an open circuit after a few months. @robin628 is right about checking grounds first though, I always start there before I even look at the connector itself. For me, a little dab on the screw threads and the washer area does the trick without risking the actual connection. Pair that with a clean ground point and you're golden for years. If you get it on the mating surfaces you're basically adding a plastic layer between the contacts which is the opposite of what you want.