Dassault-Breguet MYSTERE FALCON 900 N610RL incident near Orlando, Florida

Probable cause

Unknown maintenance personnel’s inadequate securing of a wiring bundle during a maintenance, repair, or modification event, which led to chafing of the wiring bundle, an electrical short and arcing, and a subsequent in-flight fire.

NTSB analysis

During the airplane’s descent to its destination airport, the cabin attendant noticed a “weird smell” in the galley area; she checked the appliances but could find nothing wrong with them. She then turned around and opened the area in the galley where they kept the crystal glasses and noticed a “glow behind it,” which was an electrical fire. The pilot extinguished the fire using two halon fire extinguishers, and the airplane incurred minor damage.

Examination of the area behind the crystal storage area revealed sooting, a burnt wiring bundle containing the 28-volt direct current wiring and ground wires for the cabin lighting, and a tripped circuit breaker for the cabin lighting. Two of the insulation bags in the area of the burnt wiring bundle had been fire damaged, and the wires had been routed over the insulation bags instead of directly next to the airplane's structure. The wires were also in contact with or near a soft oxygen line, which had been completely burned through. Examination of the oxygen line revealed no evidence of copper on the exposed coil; thus, the wiring had chafed against itself and not against the soft oxygen line.

During the 26 years between the completion of the airplane and the incident, numerous modifications to the lighting, interior, and galley had been made by several maintenance, repair, and overhaul organizations, which required rerouting and re-securing wiring, as well as removal and replacement of interior panels, partitions, and cabinetry near the fire. The oxygen line and wiring in the area of the fire damage had been changed from the originally specified configuration; it did not conform to the manufacturer's cabin oxygen system drawing or the manufacturer's installation standard. Further, a clamp on the oxygen line near the fire damaged area appeared to be the wrong part number clamp. A spacer and a support in this area were missing, which would have been used to achieve and maintain separation between the oxygen line and wiring.

Postincident examinations of exemplar airplanes revealed that on three of the seven airplanes, the layout of the oxygen line and electrical wiring was in compliance with manufacturer installation standards. However, on the other four airplanes, incorrect routing, spacing, or support was found, which likely occurred during maintenance.

Text from the NTSB. Open the NTSB docket for ERA15IA198 for the full record.