Narrative:

When the flight crew arrived at the aircraft; ground crew had already connected ground air hose to provide heat. The ground air was only blowing cold outside air; so I had it removed. Crew continued to prep flight as per normal and began boarding process. Boarding was taking a while; so I elected to start the APU to provide heat to the passengers already on board. This was accomplished as per normal and APU bleed was selected on after 2 minutes. A few minutes (perhaps 3-5) after selecting the APU bleed on; I began to notice an unpleasant odor; similar to that of exhaust; coming from the vents. The bleed system then automatically took itself offline (this was detected by the ceasing of airflow and sound of air passing through vents). The flight attendant then came to the flight deck and advised me that there was some smoke entering the cabin through the vents. When I looked back; I could see a light haze in the rear of the cabin. This all happened within 60 seconds or less. I shutdown the APU; directed the flight attendant to advise the rampers that we needed to deplane the aircraft; and directed the first officer to inspect the rear of the aircraft for any signs of fire or smoke at the rear of the airplane or in the inspection compartments under the tail (he found none). I made a PA announcement to the passengers and reviewed the emergency/abnormal checklist to ensure I was not neglecting to perform any other tasks. The passengers were deplaned; I wrote up the discrepancy and called dispatch. By this point the smoke had already started to dissipate. As a last precaution; I directed the first officer to call ground control and have a fire truck sent to our gate; just in case there was an unknown fire.

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Original NASA ASRS Text

Title: During preflight on a cold morning; a DHC8-300 cabin filled with smoke after the APU and air conditioning were selected ON; so the passengers were deplaned and Maintenance was called.

Narrative: When the flight crew arrived at the aircraft; ground crew had already connected ground air hose to provide heat. The ground air was only blowing cold outside air; so I had it removed. Crew continued to prep flight as per normal and began boarding process. Boarding was taking a while; so I elected to start the APU to provide heat to the passengers already on board. This was accomplished as per normal and APU Bleed was selected ON after 2 minutes. A few minutes (perhaps 3-5) after selecting the APU Bleed ON; I began to notice an unpleasant odor; similar to that of exhaust; coming from the vents. The bleed system then automatically took itself offline (this was detected by the ceasing of airflow and sound of air passing through vents). The Flight Attendant then came to the flight deck and advised me that there was some smoke entering the cabin through the vents. When I looked back; I could see a light haze in the rear of the cabin. This all happened within 60 seconds or less. I shutdown the APU; directed the Flight Attendant to advise the rampers that we needed to deplane the aircraft; and directed the First Officer to inspect the rear of the aircraft for any signs of fire or smoke at the rear of the airplane or in the inspection compartments under the tail (he found none). I made a PA announcement to the passengers and reviewed the Emergency/Abnormal checklist to ensure I was not neglecting to perform any other tasks. The passengers were deplaned; I wrote up the discrepancy and called Dispatch. By this point the smoke had already started to dissipate. As a last precaution; I directed the First Officer to call Ground Control and have a fire truck sent to our gate; just in case there was an unknown fire.

Data retrieved from NASA's ASRS site as of July 2013 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.