Warning: found out the hard way that old coax cables in a 737 can arc and start a fire under the floorboards

3 comments

3 Comments

A buddy of mine who used to work avionics on regional jets told me about a similar issue with the old RG58 coax runs near the galley area. He said the insulation degrades over time, especially where it rubs against metal brackets, and if you get a short to ground near a fuel line or hydraulic fluid drip tray, you've got a real problem. Apparently Boeing put out a service bulletin on this in the late 90s about replacing those cables with shielded twisted pair in certain zones. Crazy that older planes still have that stuff hanging around.

cora8133d ago

Gotta push back on this one hard. 99% of the time those coax runs are nowhere near fuel or hyd fluid unless someone seriously messed up the routing. The service bulletins were mostly about preventing signal interference, not because they were a fire hazard. If a short to ground was really that dangerous next to a fuel line, we'd have way more incidents than we do. Plus, swapping out old coax just for the sake of it is expensive and a lot of times the replacement cable ends up rubbing the same way unless you fix the original bracket issue.

michael8033d ago

cora813 is right about the brackets being the real problem. I've seen enough old wiring in equipment yards to know that swapping the cable type doesn't fix a bad routing path. You can put the most expensive shielded twisted pair in there and if it's still rubbing against that same sharp metal edge, you're just delaying the same problem. That said, the friend's point about the short to ground near fuel lines is still worth paying attention to. Even if it's rare, when those old insulation jackets get brittle and crack from vibration and heat, you don't need a direct short to cause a nasty arc. A little bit of moisture or fuel residue on a frayed wire can make for a bad day real quick. So yeah, the service bulletin might have been about interference mostly, but the safety angle isn't something to just shrug off either.