Many times our old airplanes are neglected in the electrical department. I'll bet every one of us can recall seeing an airplane with old, complex and confusing bundles of wiring which are virtually un-identifiable as to purpose. I've seen many more airplanes than I care to admit, with old, home-made patchwork/automotive-quality (or worse!) wiring behind/beneath/around the panel and firewalls. What does YOUR wiring harness look like?
Consider the following excerpts from an archived AOPA article:
According to the NTSB accident briefs, the pilot of a Cessna 210 reported an in-flight electrical problem and requested a descent for an immediate landing; he crashed 12 miles from the airport. The pilot and his passenger were killed.
Post-accident investigation revealed evidence of an in-flight fire, with burned or charred control wheels, glareshield, and instrument panel. The windows were rendered opaque by soot. A California Highway Patrol officer witnessed the airplane descending with smoke coming from the cabin and a "paper-like debris" falling from the airplane.
An inductive noise filter fitted to the alternator was pinpointed as the source of the fire. Accident investigators and electrical lab technicians agreed that the capacitor shorted internally and arced on the firewall. This capacitor had been installed with neither circuit protection nor electrical isolation from the airframe. The NTSB report mentions the lack of FAA parts manufacturer approval (PMA) for the item and the fact that it is not a part of the original electrical system design. Yet this item had been on the airplane for three and one-half years.
Electrical-system woes brought down another airplane, an elderly Ercoupe. Its pilot radioed the tower that he had an electrical problem and needed to land immediately. He made a base entry to the runway from which he'd just departed. Witnesses saw the airplane continue its turn into a descending spiral that continued until it impacted the ground. Smoke was observed trailing from the aircraft.
This Ercoupe's electrical system had been extensively modified among the changes, the battery had been moved from the baggage bay to the front of the firewall. According to the accident report, "Examination of [two runs of 11-gauge wire] revealed a frayed/worn-through section that matched an area of the firewall penetration hole. At another location on the wire was multistrand copper wire that had become molten and necked down to a break the wires were located on the battery side of the master relay and were without circuit protection." For this unlucky Ercoupe pilot, there was no way to stop the electrical fire once it started.
I hope this short message will prompt us all to review/audit our own airplane's electrical system and wiring. This is the FIRST step to avoid a deadly event. Consider subjecting your airplane to an Electrical System audit by another pilot or mechanic you trust. This would serve as a method of reviewing your airplane's electrical health at arm's-length from your airplane's annual inspection requirements. Perhaps that might encourage a more pragmatic view of your airplane's true airworthiness.
The SECOND step is to seriously address ourselves to correcting unairworthy deficiencies. Use only aircraft-quality components and methods. RECORD the repairs.
THEN, .... review the recommended procedures to handle inflight fires. Do you have a modern, HALON fire extinguisher in your aircraft? You do? Great!
And you also have smoke-goggles? Huh? Yes! Smoke Goggles! You can't keep flying without adequate vision, and that probably means opening windows and donning smoke goggles.
Are you mentally prepared to completely shut down your electrical system in flight ? ...(usually by turning the Cockpit Master Switch OFF.) Are you prepared to turn the FUEL OFF if the fire/smoke continues?
Are you willing to put your airplane down into a landing area OTHER THAN AN AIRPORT? While inflight, do you keep your situational awareness in order to be ever-prepared for emergency action?
And lastly... are you ready to withstand the scrutiny of the NTSB/FAA investigation of such an event involving YOUR airplane? (Answer: Go back and read the first sentence in this message and truthfully answer that question.)
(Meanwhile, I'm going out to the hangar and removing that voltage regulator noise filter whose provenance I'm unsure of.)
