Narrative:

All operations were normal up until this point. The flight attendant was doing her normal duties as well when she received several calls from passengers. There was smoke coming from the ceiling and walls of the aircraft. She immediately called us and notified as of the situation. While she was informing us I started to smell an acrid smoke. We immediately donned our O2 masks and smoke goggles. We shut off the recirculation fan shortly after that. With the memory items completed; I called ATC and declared an emergency and requested an immediate vector back to our departure airport. We turned toward the airport and started a descent. I proceeded to go through the cabin smoke QRH checklist. After that; I went through the smoke evacuation QRH checklist. Everything happened very quickly. By the time we went through the checklists; we were at about 10;000 ft and continuing the descent for landing. We requested runway xx for landing and that emergency equipment meet us. Everything was briefed and the normal checklists were accomplished. I notified the captain we would be making an overweight landed which he acknowledged and we both agreed was necessary. We called the flight attendant for an update several times as to the condition in the cabin. She told us that the smoke was indeed dissipating and had mostly gone away by the time we were less then 5 minutes from landing.based on the information; we notified the flight attendant and ATC that we were not planning on evacuating on the runway. We landed without incident and pulled off the runway onto the taxiway and stopped the airplane. Crash fire rescue equipment personnel chocked the airplane and did an external check for smoke or fire. None was found. The flight attendant confirmed that there was no more smoke coming from anywhere in the cabin. We taxied to our assigned gate with crash fire rescue equipment escorting us. When we got to the gate; we deplaned the aircraft. The smoke incident and overweight landing was written up. From what I was told initially from maintenance; the cause of the smoke was from bad bearings in the air cycle machine in pack number two. Pack number one was already deferred and not used in flight.everything went fairly smoothly in my opinion. The crew reacted appropriately. ATC and airport operations did an excellent job as well. We got the plane on the ground in a very short period of time; which is the most important thing in a situation like this. Smoke is to be taken very seriously in flight and should be treated as a fire with an unknown source. Getting the plane down quickly is the top priority.

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Original NASA ASRS Text

Title: An EMB-145 flight crew declared an emergency and returned to their departure airport when smoke was detected in the cabin and on the flight deck. When the appropriate check lists were completed the smoke abated. They had been dispatched with one pack inoperative and maintenance concluded the smoke emanated from the air cycle machine bearings in the remaining pack.

Narrative: All operations were normal up until this point. The Flight Attendant was doing her normal duties as well when she received several calls from passengers. There was smoke coming from the ceiling and walls of the aircraft. She immediately called us and notified as of the situation. While she was informing us I started to smell an acrid smoke. We immediately donned our O2 masks and smoke goggles. We shut off the recirculation fan shortly after that. With the memory items completed; I called ATC and declared an emergency and requested an immediate vector back to our departure airport. We turned toward the airport and started a descent. I proceeded to go through the cabin smoke QRH checklist. After that; I went through the smoke evacuation QRH checklist. Everything happened very quickly. By the time we went through the checklists; we were at about 10;000 FT and continuing the descent for landing. We requested Runway XX for landing and that emergency equipment meet us. Everything was briefed and the normal checklists were accomplished. I notified the Captain we would be making an overweight landed which he acknowledged and we both agreed was necessary. We called the Flight Attendant for an update several times as to the condition in the cabin. She told us that the smoke was indeed dissipating and had mostly gone away by the time we were less then 5 minutes from landing.Based on the information; we notified the Flight Attendant and ATC that we were not planning on evacuating on the runway. We landed without incident and pulled off the runway onto the taxiway and stopped the airplane. CFR personnel chocked the airplane and did an external check for smoke or fire. None was found. The Flight Attendant confirmed that there was no more smoke coming from anywhere in the cabin. We taxied to our assigned gate with CFR escorting us. When we got to the gate; we deplaned the aircraft. The smoke incident and overweight landing was written up. From what I was told initially from Maintenance; the cause of the smoke was from bad bearings in the air cycle machine in pack number two. Pack number one was already deferred and not used in flight.Everything went fairly smoothly in my opinion. The crew reacted appropriately. ATC and Airport Operations did an excellent job as well. We got the plane on the ground in a very short period of time; which is the most important thing in a situation like this. Smoke is to be taken very seriously in flight and should be treated as a fire with an unknown source. Getting the plane down quickly is the top priority.

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.