Narrative:

While taxiing in to the gate; the first officer pressed the start switch for the APU. We were both caught a little off guard because it activated the bbpu (bus bar protection unit) and removed the left bus from the system. Since I have seen this before on APU startup; we reset the bus tie and gained all systems back. At this point I noticed the starter light for the APU was still illuminated and the APU was not running. I instructed the first officer to depower the APU and loads and voltages all looked normal. We parked at the gate and I requested a gpu which was hooked up. We checked the APU power on again the starter light illuminated again. We depowered it and again all voltages and loads returned to normal. I contacted maintenance about the issue and as I was writing up the issue in the logbook; the check fire detect light illuminated but there was no associated fire warning light on the fire panel. About 10 seconds later an odor of burning electrical insulation permeated the flight deck and the fire warning light illuminated for the APU. I immediately followed the immediate action items for an APU fire and since only the flight crew was left; I instructed them to exit the aircraft. My first officer called for the fire trucks and since I was on the phone with mx; told them of the situation. I exited the aircraft and went to the tail to verify the issue and witnessed smoke coming from all of the APU bay vents; but no flames. The maintenance crew confirmed the contactor had welded and the starter had overheated.

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Original NASA ASRS Text

Title: Dash-8-300 Captain reported experiencing a fire in the APU at gate arrival related to the APU starter overheating.

Narrative: While taxiing in to the gate; the FO pressed the start switch for the APU. We were both caught a little off guard because it activated the BBPU (Bus Bar Protection Unit) and removed the left bus from the system. Since I have seen this before on APU startup; we reset the bus tie and gained all systems back. At this point I noticed the starter light for the APU was still illuminated and the APU was not running. I instructed the FO to depower the APU and loads and voltages all looked normal. We parked at the gate and I requested a GPU which was hooked up. We checked the APU power on again the starter light illuminated again. We depowered it and again all voltages and loads returned to normal. I contacted Maintenance about the issue and as I was writing up the issue in the logbook; the check fire detect light illuminated but there was no associated fire warning light on the fire panel. About 10 seconds later an odor of burning electrical insulation permeated the flight deck and the fire warning light illuminated for the APU. I immediately followed the immediate action items for an APU fire and since only the flight crew was left; I instructed them to exit the aircraft. My FO called for the fire trucks and since I was on the phone with MX; told them of the situation. I exited the aircraft and went to the tail to verify the issue and witnessed smoke coming from all of the APU bay vents; but no flames. The Maintenance crew confirmed the contactor had welded and the starter had overheated.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.