from the bodies revealed high levels of cyanide, fluoride and carbon monoxide, chemicals produced by the burning plane. Investigation Because the accident occurred in the United States, it was investigated by the National Transportation Safety Board (NTSB). Although the fuselage was nearly destroyed by the intensity of the fire, the cockpit voice recorder (CVR) and flight data recorder (FDR) were still in good condition and produced vital data for the NTSB investigation. On the CVR, NTSB investigators heard eight sounds of electrical arcing beginning at 18:48. The arcing sounds repeated each time that the crew tried to reset the lavatory circuit breakers. Both pilots testified that they did not hear any arcing, and the NTSB concluded that these sounds would be inaudible to the flight crew. Although a number of wires in the lavatory section were later found with insulation stripped away, NTSB investigators were unable to determine whether this insulation damage was the cause of the fire or was caused by the fire. This particular DC-9 had experienced a number of problems over the months leading up to the incident; 76 maintenance reports had been filed in the plane's logs in the previous year, and the CVR recorded Captain Cameron telling First Officer Ouimet to "put [the tripping breakers] in the book there" when the breakers failed to respond to the first reset attempt at 18:52. Cameron attempted once more to reset the breakers at 18:59. The CVR recorded arcing sounds followed by the popping sound of the breakers continuing to trip again after each reset over the next 60 seconds. On 17 September 1979, the plane, then serving as Air Canada Flight 680 from Boston, Massachusetts, to Yarmouth, Nova Scotia, had suffered an explosive decompression in the rear bulkhead that required rebuilding the tail section and replacing or splicing most of the wiring and hydraulic lines in the back of the plane. Cameron later noted that the Air Canada maintenance crew "did a heck of a job getting everything put back together" after the decompression incident. Investigators were unable to find signs of arcing in any of the wire splices from the repairs done four years earlier, though much of the wiring in the rear of the plane was severely damaged or destroyed by the fire itself. Initial findings The NTSB was ultimately unable to determine the origin of the fire. In August 1984, the NTSB issued a