Electrical arcing forced a United Airlines B767-300 on a planned Jan. 9, 1998, ETOPS [extended operations] flight from Zurich to Washington, D.C., to make an emergency landing at London's Heathrow Airport. Investigated by the UK's Air Accidents Investigation Branch [AAIB], the August 2000 final report captures many of the typical elements associated with in-flight electrical arcing and fires. This particular emergency stemmed from a food chiller installed in the electronic and equipment [E&E] bay the day before by two mechanics at Washington's Dulles Airport. They had never performed this task before and did not strictly follow the maint-enance manual. A jagged edge on the chiller scraped insulation off some of the wiring as the chiller was pushed into position.

Pertinent extracts from the AAIB report (numbers equate to sections in the report):

• 1.11 Despite the number of recorded parameters, the DFDR [digital flight data recorder] contained no information that was of assistance in determining the cause, or the time of initiation, of the electrical failure.
• 1.12.3.6 Examination throughout the E&E bay revealed the presence of small curled aluminum swarf, typical of that produced from the drilling of holes. [Swarf is the industry term for drill shavings.]
• 2.3.3 Localized extreme temperatures within the [wiring] loom probably existed in flight for at least 30 minutes, supporting the concern that further wiring damage could have occurred to previously undamaged wires should the flight have continued for a longer period of time. The ETOPS clearance for the Boeing 767-300 is that it should always remain within a distance equivalent to 180 minutes single engine flying time from a suitable diversion airfield.
• 2.3.4 The concentration of smoke in the E&E bay throughout the event had not been sufficient to activate the sole smoke detector for the bay.
• Finding #12. Arc-induced copper 'spatter' could rapidly spread fire effects to adjacent areas.