Date: 201904
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: Q400
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Aircraft component: APU Pneumatic System & Ducting
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Time Pressure; Communication Breakdown; Workload
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Attendant; Person Flight Crew
When detected: Other Pre Taxi
Result: General Evacuated; General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Shortly after selecting APU BL AIR OPEN; CABIN DUCT HOT and FLT COMPT DUCT HOT cautions illuminated. In the flight deck; there was the familiar smell of hot bleed air; but it didn't seem out of the ordinary except that it might have been a little stronger than normal.APU BL AIR was selected OFF and the RECIRC fan was checked to make sure it was on. Temperatures on both ducts were reading 70 Celsius [degrees] and not decreasing.Shortly thereafter; Flight Attendant A reported smoke in the cabin. Looking back from the flight deck; the air in the cabin appeared gray and misty.The Captain elected to deplane the passengers through the main cabin door. Deplaning was uneventful. Eternal power was connected and the APU was shut down.Emergency personnel were called and arrived after a few minutes.Maintenance personnel opened the aft doors and the smoke dissipated quickly. They restarted the APU and opened the bleed air with the same effect as the flight crew had experienced.Passengers' belongings were removed from the aircraft and relocated to a new aircraft. The flight was then operated uneventfully with that aircraft. The APU bleed problem by itself would have been stressful enough to deal with; but there were additional distractions that probably delayed my reaction to problem.At the time of the event; I was on the phone with Dispatch regarding weather issues; which were themselves compounded by a malfunctioning fuel quantity indicator and inoperative EFBs that made communication a little more difficult.Also; there was a stuck mic on station frequency; which further inhibited communication.At the time I selected APU BLEED AIR to OPEN; I was on the phone with Dispatch. I had to use my cell phone as the EFBs were inoperative. With the bleed air on; the flight deck was noisy. I asked the First Officer to close the flight deck vents to reduce noise. When we saw the ducts were hot; we reopened the vents and checked to make sure the recirc fan was on (I can't remember if it was).I delayed the decision to deplane for a moment because I was worried about containing the passengers on the ramp; but I decided that it was urgent that I not have people on the airplane with smoke from an uncertain source.I made the announcement to deplane from the front of the cabin without first advising Flight Attendant B. I did not advise the passengers to leave all their belongings; but I did ask them to move in an orderly fashion and to stay close to the airplane. I did not contact Ground Services to help contain the deplaned passengers; though I did notice some ground personnel approaching the airplane soon after deplaning began.In retrospect; I wish I had made a more thorough deplaning announcement; but on the other hand; I am glad that I didn't waste much time in getting the people off the airplane. I also wish I had called for firefighters. After deplaning the passengers; someone asked me if I had called them. I answered no and he said he would do it for me.All company personnel were very helpful and professional.I have operated the APU with bleed air open and recirc fan off in the past for short spans of time to help communication in the flight deck (e.g. getting a clearance; calling CLP/dispatch) and have never gotten hot ducts or smoke in the cabin. Maybe this is a place to be more cautious in the future.I'm glad that I have spent time in the past thinking of how to handle emergencies at the gate. We don't have specific procedures for handling such events and we don't train them.There was a moment when I thought I could try to evacuate the smoke and continue with the operation in that airplane. That did not last long and I decided to get the people out right away. Maybe the lesson is; don't mess with smoke.This event was good practice in prioritizing tasks. My attention was consumed by four different MEL's and talking with several different people about their part in dealing with the various pieces of malfunctioning equipment on the airplane. There were also communications problems as noted above. When the FA said there was smoke on the plane; I had to drop all that and switch into a completely different mode. Without our training and time spent imagining various emergencies; it would have been harder to make this transition.




Synopsis: Bombardier Q400 Captain reported orderly evacuation due to smoke in the passenger cabin.