Let’s discuss circuit breakers (CB). We routinely verify during the prestart check that they are pushed in or appropriately disabled. Most of the time this is perfunctory and it’s a boring topic – sorry. Read on.
In the recent landmark accident CBs and wiring were implicated. Note that the rules regarding CBs have changed – In years past, if a CB popped the practice was to let it cool and reset ONCE on the theory that it might be a transient fault. No more. If a CB pops, unless it’s flight critical, do NOT reset. There have been only a few instances of big in-flight electrical fires where the aircraft and lives were lost. In this case, the tab was about $20 million and the lawsuits are flying. Seems like a lot for a simple thermal-mechanical device.
If you smell burning insulation before disabling the appropriate CB, the aircraft should be grounded until the fault has been isolated and the affected wiring replaced. That’s probably going to be expensive. But, if that seems harsh, according to NTSB engineers, once the wiring is hot enough to melt insulation so you can smell it – the insulation is toast, if you’ll pardon the pun. It will no longer function as intended and there is a fair chance that other circuits or equipment may malfunction and cause a fire when you least need it. Don’t forget that on-board fire extinguisher – this is potentially an extremely serious fault. Remember where it is? Can you reach it? Is it properly charged? Again – boring but critical.
Wiring is like props – we take them for granted and they routinely perform with little complaint until something unfortunate happens suddenly. Also suggested reading is ASF’s new In-Flight Electrical Fires Safety Brief on the topic. It’s a short read.
If you have a wiring story, please share it. Many others may benefit.