Date: 201502
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Light: Night
Aircraft: Dash 8-400
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Ground Personnel
When detected: Aircraft In Service At Gate
Result: Flight Crew Became Reoriented
Contributing factors: Company Policy; Human Factors
Primary problem: Company Policy

Narrative: Prior to boarding our APU failed for a second time. We called maintenance and they deferred the APU. We boarded and handed out paper work when we found out the ground crew lost the pin to the door handle. The ground crew asked us to call maintenance to see if they had spare pins. I called dispatch who then handed me over to maintenance. Maintenance advised me that they would send the mechanics out to help look. While on the phone with maintenance I asked if it was okay with them for us to start an engine because the cabin temperature was dropping rapidly. They said they didn't see a problem with it. I asked the ground crew if it was okay to start engine #2 and they confirmed we were good to start and the aircraft was chocked and hooked up to the tug; but then they walked away. I went outside to make sure #2 was clear and the First Officer (FO) started the engine. While outside I looked around to see if I could see the pin. The mechanics showed up and starting looking for the pin to the door. After a while of looking we could not find the pin and the mechanics disappeared without talking to the crew. I called dispatch to see what was going on and to see if there was any spare pins; or planes we could take. That's when dispatch advised me that we would probably be swapping planes. I told the FO and he called operations to ask for the jet bridge back to deplane. A few minutes later the gate agent comes down and we deplane. After the last passenger gets off I go to the back of the aircraft to advise the flight attendants what was going on. At that point in time the flight attendants advised me of a possible duty issue for them. A few minutes later the FO came back to tell us that operations had called and we are switching aircraft. A couple of minutes after that a mechanic ran on board and asked why the #2 was still running. Not knowing it was still running I ran up there and quickly shut the engine down. We then shut down the aircraft and took our bags off and proceeding into the terminal with no incidents. Better communication. Create a checklist for situations like this to warm the aircraft when an APU is MEL'd in extreme cold conditions.


Second narrative: The APU on the plane died twice and resulted in Maintenance deactivating it. As the passengers boarded; the temperature in the plane was dropping by the time reached 46 degrees we knew we had to do something. Due to no working air carts to heat the plane and finding out the plane next door also had started its #2 engine; we decided it would be best to start the #2 engine. We advised the rampers of our decision and once the Captain made sure the area was cleared and the beacon was on; we started the #2 engine. Once finished loading the rampers couldn't find the handrail's door pin; due to its loss and cold windy temperatures it was decided to deplane for the sake of our passengers. The captain was talking to maintenance and was searching for the pin too. After the last passenger left ops called and told us that we will be changing planes. I went to the middle section of the plane around the exit row to advise the captain and flight attendants of the change. Maintenance came on the plane and advised the captain that the #2 engine was still running and he ran up and turned it off. The airplane was never unsupervised as the entire flight crew was on board the plane but I can see how not being seated at the flight deck the entire time could possibly lead to problems even with no passengers. The temperature outside was around 6 degrees Fahrenheit with gusting winds played a huge part in our decision in starting the #2 engine to heat the plane. I wished that the APU worked or they could have had a working air cart but unfortunately it was our only chance for some heat.


Synopsis: Dash 8 flight crew reported starting an engine for cabin heat on the ground; then leaving the engine unmonitored when they left the cockpit.