What happened
While descending prior to approaching Newark, New Jersey, the crew of a Boeing 737 attempted to start the Auxiliary Power Unit (APU). This initial attempt failed to produce a start. Later, during the landing roll after touchdown at Newark Liberty International Airport, the crew made another attempt to start the APU. This second attempt triggered a fire warning light on the flight deck.
Although the crew discharged the fire extinguisher bottle, the fire warning indicator remained illuminated. Consequently, the captain ordered an evacuation while the aircraft was parked on a taxiway. During the evacuation, some passengers exited through the overwing exits without crew assistance. Several of these passengers sustained injuries while climbing down onto the wing structure.
The investigation
Post-accident inspection of the APU revealed no evidence of actual fire damage to the unit itself. However, post-accident testing provided critical mechanical findings. The test results indicated that the turbine blades were burned and eroded. Additionally, the fuel control cracking pressure was found to be set higher than the specified limit. Investigators also discovered that the electrical harness wires connecting to the fuel solenoid connector had been reversed.
Findings
The sequence of events suggests a mechanical or installation error in the APU system rather than an actual fire event. The reversal of the electrical harness wires likely contributed to the malfunction during the start attempt, which subsequently triggered the warning system despite the absence of thermal damage.