Dash 8 Series Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Aircraft Aircraft Damaged; General Maintenance Action
Aircraft
After taxiing into the gate I noticed the APU hadn't started. The FO thought he hit the start button. After waiting; it appeared the APU panel was off; so I powered it down/up and began the start sequence again. The cabin door was open and a ramp manager said smoke was coming out of the APU exhaust port. I powered off the APU. Seeing no fire indications on our cockpit panel; I told the ramp supervisor to tie the prop and FA to begin deplaning without delay. There was no gate agent available after several calls. When the last few passengers were just about off; the APU check fire detect warning light illuminated but no fire light illuminated. I told the FO to call for fire trucks; depowered the aircraft; and got the remaining crew off. I confirmed the black smoke coming from the APU exhaust port which quickly dissipated. No fire had initiated; just smoke and the fire bottle and discs did not discharge.The APU starter/generator had a welded starter contactor that overheated and began smoking. It was a mechanical issue. We have significant APU issues amongst the Dash 8 fleet. Recommend better APUs and gate agents ready at the gate when we arrive. We took an unnecessary delay getting people off the plane because a gate agent wasn't there to receive passengers. Had we taken any more delay I was on the brink of ordering an emergency evacuation had it actually caught on fire.
Dash-8 Captain reported smoke emitted from the APU exhaust port after gate arrival. Passengers were deplaned and the starter contactor was later found to have overheated.