Narrative:

I was doing operating experience for the captain. We pushed off of the gate and all the checklists were completed; we started to taxi to the runway in the configuration of #2 engine with APU off. We had taxied about a hundred yards when we received a single chime call from the cabin. It was our aft flight attendant. She said that she was smelling smoke; a sulfur smell like someone had lit a pack of matches. I told her to call back if it got worse and we were turning around to get back to the gate. I told the captain and he stopped the aircraft as I made the call to ATC; requesting the turn. They granted the request and I asked for the trucks. I made a quick call to operations to advise them and ask for a quick park back at our gate.ATC asked about declaring an emergency; and I replied yes and the trucks. He said they were on the way. During this the captain was taxiing us back around and we saw on the ecs page the right pack was warmer than should be expected; I saw 52 degrees and he shutoff the pack for us. As I was talking to ATC and the company; the captain made a call back to the flight attendants and he said they thought it was getting better so we elected to roll back into the gate. Another aircraft had pushed behind us so operations cleared us back into our gate. The station was quick in getting us back in and getting an agent right there with the jetway. Report from the back; it was getting better. We deplaned in a normal manner.the firemen said the outside looked clear and they searched the cabin. No signs of a fire. We happened to have a company mechanic in the aircraft as a passenger. He was the last to come to the front. He was fairly confident that the bearings in the right pack had gone. I called dispatch to report the event and started the process with maintenance. As we waited for the local mechanic to get to us; the firemen and I searched the aircraft again for any hot spots and nothing unusual was found. The firemen stayed around for the trouble shooting.it was determined that the right pack was the culprit; and the rest of the environmental system was sound. The mechanic worked on the deferral for the pack and dispatch worked on a new plan for us. We added the required fuel and finally boarded the flight again. The passengers were communicated to throughout; about our return; at the gate in deplaning; and after they were back on board.

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Original NASA ASRS Text

Title: A CRJ900 flight crew declared and emergency and returned to the gate for maintenance following a Flight Attendant advisory of noxious fumes in the cabin on initial taxi.

Narrative: I was doing Operating Experience for the Captain. We pushed off of the gate and all the checklists were completed; we started to taxi to the runway in the configuration of #2 engine with APU off. We had taxied about a hundred yards when we received a single chime call from the cabin. It was our aft Flight Attendant. She said that she was smelling smoke; a sulfur smell like someone had lit a pack of matches. I told her to call back if it got worse and we were turning around to get back to the gate. I told the Captain and he stopped the aircraft as I made the call to ATC; requesting the turn. They granted the request and I asked for the trucks. I made a quick call to Operations to advise them and ask for a quick park back at our gate.ATC asked about declaring an emergency; and I replied yes and the trucks. He said they were on the way. During this the Captain was taxiing us back around and we saw on the ECS page the right pack was warmer than should be expected; I saw 52 degrees and he shutoff the pack for us. As I was talking to ATC and the company; the Captain made a call back to the flight attendants and he said they thought it was getting better so we elected to roll back into the gate. Another aircraft had pushed behind us so Operations cleared us back into our gate. The station was quick in getting us back in and getting an agent right there with the jetway. Report from the back; it was getting better. We deplaned in a normal manner.The firemen said the outside looked clear and they searched the cabin. No signs of a fire. We happened to have a company mechanic in the aircraft as a passenger. He was the last to come to the front. He was fairly confident that the bearings in the right pack had gone. I called Dispatch to report the event and started the process with maintenance. As we waited for the local mechanic to get to us; the firemen and I searched the aircraft again for any hot spots and nothing unusual was found. The firemen stayed around for the trouble shooting.It was determined that the right pack was the culprit; and the rest of the environmental system was sound. The mechanic worked on the deferral for the pack and Dispatch worked on a new plan for us. We added the required fuel and finally boarded the flight again. The passengers were communicated to throughout; about our return; at the gate in deplaning; and after they were back on board.

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.