Aviation Investigation Report A98H0003

2.17.2  Arc-Damaged Cables and Wires

Each of the arcs on the recovered 20 cable and wire segments was analyzed to determine whether it could have been the cause and origin of the fire, or whether the arc was created as a result of the fire. This process involved attempting to identify the system to which each of the arced cables and wires belonged and, where possible, its installed location in the aircraft.

Three arced wires were determined to be from particular aircraft systems, and the arc locations were accurately positioned in the aircraft. Had any of the three wires been involved in a lead arcing event, the pilots would most likely have noticed the associated loss of function, or the failure event would have been recorded on the FDR. There is no indication that either occurred.

There were nine arced wires for which no definitive location within the aircraft could be determined. For several of these nine arced wires, the arcing event could be reasonably linked to one of the known system-related failures captured on the FDR during the 92 seconds between the first recorded failure and the stoppage of the FDR recording. As these recorded failures occurred about 14 minutes after the initial detection of an unusual smell in the cockpit, these failures and associated arcs were determined not to be involved directly in the lead ignition event.

The remaining eight cable and wire segments with arcing damage were from the IFEN installation. The individual PSU cables and the control wire were assessed for possible involvement in the initial arcing event. Most of the arcing on the IFEN cables and wires could be attributed to fire-related damage; however, the arc located at 9 cm (3.5 inches) from the end of the Exhibit 1-3791 IFEN PSU cable segment could not be attributed to fire-related damage. Regardless of which conduit was used for the routing, with the cables and wires positioned as described in Section, this arc would have occurred just forward of manufacturing station (STA) 383, above the right rear cockpit ceiling just outside the forward end of the conduit.

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