Narrative:

In descent below 10;000 ft at 250 KTS; first officer started APU; waited 2 minutes; then switched over the bleeds from 10th stage to APU. At the same time; we both noticed a puff of smoke wave across our faces. We paused for a moment to see if we would get the smoke toilet caution message; and we did. First officer proceeded to perform the non normal checklist for smoke toilet. Meanwhile; I contacted approach and asked for a vector to the OM and reported we had smoke in the lavatory. Approach gave me lower and a turn. At this time he asked me if we needed assistance. I replied yes we should roll the trucks. The flight attendant somewhere in this timeframe called up and reported smoke in the cabin. I informed the flight attendant at this time the smoke toilet caution light was on. She responded with 'I will go back and check it out.' she did so; and by the time she called back to report; she stated the smoke had dissipated and there was no fire in the lavatory; and by this time the EICAS message 'smoke toilet' was gone at approximately 800 ft AGL. We proceeded to land and taxi to the gate where crash fire rescue inspected the plane for heat and fire inside the lavatory and cargo area. We kept the passengers on board while crash fire rescue checked out the plane. At this time we recognized we were not in imminent danger and rather than deplane on the ramp where there was snow and ice buildup; we waited for the jetway to deplane. I assume it was oil leakage from a seal on the APU or engine; not sure. The smoke was white in color and had an oily smell; not a fire smell.

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Original NASA ASRS Text

Title: A CRJ-200 crew experienced smoke in the cockpit; the lavatory smoke alarms sounded and a Flight Attendant reported cabin smoke. This occurred shortly after air conditioning bleeds were selected to APU from engine. An emergency was declared.

Narrative: In descent below 10;000 FT at 250 KTS; First Officer started APU; waited 2 minutes; then switched over the bleeds from 10th stage to APU. At the same time; we both noticed a puff of smoke wave across our faces. We paused for a moment to see if we would get the Smoke Toilet Caution message; and we did. First Officer proceeded to perform the Non Normal checklist for Smoke Toilet. Meanwhile; I contacted Approach and asked for a vector to the OM and reported we had smoke in the lavatory. Approach gave me lower and a turn. At this time he asked me if we needed assistance. I replied yes we should roll the trucks. The Flight Attendant somewhere in this timeframe called up and reported smoke in the cabin. I informed the Flight Attendant at this time the Smoke Toilet Caution light was on. She responded with 'I will go back and check it out.' She did so; and by the time she called back to report; she stated the smoke had dissipated and there was no fire in the lavatory; and by this time the EICAS message 'Smoke Toilet' was gone at approximately 800 FT AGL. We proceeded to land and taxi to the gate where Crash Fire Rescue inspected the plane for heat and fire inside the lavatory and cargo area. We kept the passengers on board while Crash Fire Rescue checked out the plane. At this time we recognized we were not in imminent danger and rather than deplane on the ramp where there was snow and ice buildup; we waited for the jetway to deplane. I assume it was oil leakage from a seal on the APU or engine; not sure. The smoke was white in color and had an oily smell; not a fire smell.

Data retrieved from NASA's ASRS site as of April 2012 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.