Dash 8-300
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 220; Flight Crew Total 7200; Flight Crew Type 6600
Situational Awareness; Time Pressure
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew Overcame Equipment Problem; General Evacuated
Aircraft
After engine start; we noticed the APU contactor was welded; we quickly de-powered the aircraft and asked all the passengers to deplane. During the deplaning process; the ramp supervisor advised me that he sees a lot of smoke coming from the APU area. At that point we were almost finished deplaning all passengers except 3 that came on with wheelchairs (they were still seated). At that point in time; I decided to activate the APU fire bottle on the side of caution knowing I have a few passengers that were still on the plane with mobility issues. Fire services were also called and inspection was also done by the firefighters to ensure no fire was present.
After engine start crew noticed that the APU wouldn't shut off and there was an excessively high load. We suspected APU contact weld. Upon detection of this problem we started to deplane and during the deplaning process a ground personnel announced there was smoke coming from the back of the aircraft. Since we had passengers that required the ramp and the ramp had already been taken away; the captain elected to discharge the APU fire bottle as a safety measure. The aircraft was powered down immediately following the APU fire bottle discharge. During this time; I was assisting the wheel chair passengers with going down the stairs as quickly and safe as possible. AARF was called and met the aircraft
Bombardier Dash 8 flight crew reported shutting down the APU and discharging the fire bottle after noticing an excessive electrical load on the APU and smoke reported to be coming from the tail area.