Dash 8-200
Flight Crew Air Transport Pilot (ATP)
Time Pressure; Confusion
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Aircraft Equipment Problem Dissipated; Flight Crew Landed in Emergency Condition; Flight Crew Diverted; Flight Crew FLC complied w / Automation / Advisory; General Declared Emergency
Aircraft
We had just left 14;000 FT descending to 9;000 FT. Not long after we started descending I noticed an odor in the cockpit. At first I thought the air conditioning had gone to full hot and was pumping out heat. I checked the duct temp and it was showing below 20 degrees. Right after that the Flight Attendant called and said the cabin was filling up with smoke. Shortly thereafter; smoke appeared in the cockpit coming through the First Officer's lower air duct. We then proceeded to secure the aircraft and completed the required checklist to vacate the smoke. About 3 or 4 minutes had passed and the Flight Attendant reported no change in the amount of smoke in the cabin. With a major airport being the closest airport; we advised ATC of our situation declared an emergency. About 5 min from landing the Flight Attendant informed us the cabin was secure and that the smoke was finally clearing out. Landing was uneventful. After landing; the fire crew checked out the aircraft and we informed them that the smoke had stopped. We then taxied to the gate with the fire crew. Once at the gate passengers were met and brought into the gate area.  All passengers appeared to be OK as they deplaned. No one was complaining about any health issues.I believe the smoke was coming from the bleed air system. Flight Attendant notified us of the smoke in the cabin; we then proceeded to the checklist; shut down the bleed air system as we descended to 9;000 FT.
A DHC-8-200 Flight Attendant reported the cabin filling with smoke shortly before smoke entered the cockpit during descent. An emergency was declared; the QRH completed and as the flight diverted to a nearby airport the smoke began dissipating.