Incident Details
After landing, the crew taxied the aircraft to the gate and started the auxiliary power unit (APU) normally. During taxi, the number 3 pneumatic duct failure light illuminated. Later, the center accessory compartment (CAC) door warning light came on, and ground personnel observed smoke emanating from the fuselage outflow valves. Following engine shutdown, smoke entered the cabin and the APU tripped off. Fire department personnel found the CAC outside door hot. Using the cabin floor hatch, they observed flames 1-2 feet high inside the CAC. The fire was extinguished, with damage limited to the CAC.
Investigation Findings
The investigation revealed an improper or loose battery ground connection. Normal cable movement during battery disconnection would loosen the connection. Burned insulation blankets met specifications but were coated with synthetic hydraulic fluid, from a slat actuator leak, and jet fuel. The fire pattern suggested fuel seepage along a bulkhead fastener line. The battery ground had last been installed in November 1987. The battery had last been charged two weeks before the incident. A relevant service bulletin pertaining to the battery ground had not been complied with. Inoperative CAC drain valves allowed fuel to pool in the CAC bilge. No CAC fire warning or extinguisher system was installed.