Air Carrier flight crew reported APU fire while parked at gate awaiting departure.
Synopsis
Air Carrier flight crew reported APU fire while parked at gate awaiting departure.
Narrative
During preflight crew noted and discussed 'APU Control' status message deferred across multiple flights. On arrival at aircraft; status message was still displayed and deferred. We called Maintenance to come out and try to clear the message.Maintenance arrived and troubleshot message by accessing the Avionics compartment. Following this action; we now had an additional Status Message of 'APU start system.' This deferral necessitated flight planning to run the APU for the entire flight. I advocated with maintenance to fix it or resolve it but was told that maintenance had decided to go as is.Cargo offloaded; additional fuel boarded; and the gate agent closed the cabin doors and pulled the jetway. As we were waiting for the FWD cargo door to be closed; the aircraft lost all power. We reestablished ground power as the ground power lines were still plugged-in to the aircraft. We had no indication of what had happened other than the APU had shut down and we had a yellow APU Status light at the APU selector switch. We assessed the EICAS and available information and decided the APU had auto-shutdown for some unknown reason.I exited the cockpit to make a PA explaining the power loss and calm the pax. When I returned to the cockpit; my FO (First Officer) told me that the tug driver had come on the intercom and told us there were sparks and flames coming from the tail. I directed the FO to call for CFR (Crash Fire Rescue); have the jet bridge brought up to the aircraft; and advise ramp that we may be evacuating.I went back into the cabin and briefed the Purser. She noted and reported an acrid fire smell throughout but no visible smoke in the cabin. We agreed that it was our strong desire to have the pax egress through the jet bridge once it was attached; and that we would have the pax leave everything behind and just walk off the aircraft. Once the jetway was attached and door 2 was open; I made a PA telling the pax to stand and walk off the airplane; leaving everything behind. Once all the pax were off the aircraft; we did a cabin inspection to be sure everyone was off and then exited the aircraft.In the gate area; I made another PA; and debriefed the FAs and flight crew; all of whom did an outstanding and highly professional job. I noted to the flight attendants that it was their calm demeanor and professional bearing that inspired confidence in the passengers and led to a smooth egress. I then went to the ramp to assess the condition of the aircraft. I spoke with the Fire Chief who informed me that the fire was out; and it was safe for the passengers to return to the aircraft to retrieve their personal belongings. This was also when I was informed that someone (I presume the ramper) had seen the fire and went to the nose gear and shut down the APU and discharged the APU fire bottle. Kudos are due to this professional who knew his job and took action.The passengers were allowed back on the aircraft to retrieve their personal items and bags. All crew also retrieved their equipment and exited.
Second reporter narrative
Flight was released w/APU Control Sys status message. After starting APU; APU Start Sys status appeared. Maintenance deferred system; now requiring APU to run continuously during flight. After fueling to new release fuel; and getting ready to go; burning smell appeared in flight deck; followed by the APU auto shutting down. Since ground power was still plugged in; we reestablished power to the airplane. Called maintenance on the radio to inform them of issue; and they replied 'that explains the sparks'. Ground crew then confirmed we had sparks and smoke coming from the APU. Shortly after that the APU BTL DISCHARGE light illuminated. We evacuated the aircraft via jetway.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.