B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 218
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
General Maintenance Action
Aircraft; Human Factors
During preflight checks Maintenance was troubleshooting an inoperative APU. We just started boarding when the rear Provisioning Agent working the rear galley yelled; 'APU fire' to one of the Flight attendants. The rear Flight Attendants; along with a Deadheading Captain ran to the flight deck to tell the Mechanic about the APU fire. The Mechanic shut down the APU and pulled the fire switch and then ran to the back of the aircraft to assess what was going on with the APU. As the Mechanic left the cockpit; the First Officer discharged the APU Fire Bottle. There was no Fire Warning bell or any other fire indication in the flight deck. Apparently there was some residual fuel in the APU because of previous failed start attempts and that created the appearance of a fire when the mechanic successfully started the APU. After the event Maintenance deferred the APU Fire Suppression System and returned the aircraft to service with the deferred items.
[Report narrative contained no additional information.]
B737 flight crew reported discharging the APU fire bottle when residual fuel from a failed start created the appearance of a fire during the APU start.