When the flight attendants reported smoke in the cabin during taxi-in; the flight crew of a DC9-50 stopped their taxi; requested CFR response and conducted a preliminary evacuation check list; stopping just short of ordering an evacuation; pending evaluation of their ameliorative measures. When the smoke abated following the shutdown of all air conditioning sources the aircraft was towed to the gate for deplaning and maintenance.

Narrative

After clearing the inboard runway the right engine was secured and APU air was supplied to the right A/C pack. After a short taxi we received a call from the cabin to inform us that there was smoke in the cabin and passengers were attempting to get up. I brought the aircraft to a stop; informed Ground of the situation; and requested CFR. I asked Ground Control if they could determine if any smoke or flames were visible from our aircraft. The response was negative; and that everything looked normal. There were no abnormal indications on the flight deck; and while the First Officer indicated that he thought he could smell something; I did not detect any odors. We turned off the APU air and both A/C packs. I contacted the flight attendants on the intercom to get an update and additional information on the status of the cabin and passengers. I instructed them to keep everyone seated; let them know that CFR would be arriving very shortly; and that an emergency evacuation may eventually be required. I made a PA to the passengers to remain seated; told them that we were working on the situation; and that emergency equipment would be around the aircraft shortly. We used the viewport to assess the cabin contamination; and noted that CFR was arriving on scene. I called for and conducted the emergency evacuation checklist; but did not call for the actual evacuation at this time. I wanted to slow things down and determine whether our previous actions of turning off all air sources and unpowering all but the emergency electrical buses had or would produce any positive results in the cabin. At this point we opened the flight deck door for better cabin access and assessment. I immediately noticed the odor and characteristics of the fumes. I was familiar with the smell and the obscuration; and it indicated to me an air conditioning/pack overheat or abnormality. I had no sense of fire or combustion; and none of the passengers or crew appeared to be in any physical/breathing distress. In fact; to the contrary; I could see a number of passengers calmly sitting; legs crossed; recording the event on their camera phones. It appeared that the situation was stabilized; and although the odor was strong and cabin visibility poor; it was certainly not deteriorating. I felt the safest course of action was to not evacuate. I asked CFR personnel to closely inspect the aircraft including dropping the aft air stairs for tailcone access. The situation rapidly de-escalated and our company technical operations personnel were now on the scene. Ventilating the cabin for passenger comfort became our primary concern; as it was over 90F outside with no air on the aircraft. The First Officer went into the cabin to accomplish this. After consulting with CFR and our tech-ops people and with the cabin free of all contaminants; we elected to have the aircraft towed into the gate; with the passengers remaining on board.