SMOKE IN COCKPIT AND CABIN MANDATES A RETURN AND LAND EMER SITUATION.

Narrative

ON TKOF RWY 18R; MEM; TN; SMOKE OF UNKNOWN ORIGIN WAS NOTED IN THE COCKPIT AND SIMULTANEOUSLY RPTED FROM AFT JUMPSEAT. ACFT IMMEDIATELY BEGAN AN EMER RETURN TO LAND RWY 27; MEM; REQUESTING FIRE TRUCK ASSISTANCE. INTERPHONE CONTACT WAS MAINTAINED WITH THE FLT ATTENDANT WHO RPTED THAT INSPECTION COULD NOT REVEAL THE SOURCE OR TYPE OF SMOKE IN AFT CABIN; CALLED; OR LAVATORIES. SMOKE WAS NOT PROFUSE AND LATER STABILIZED. EMER WAS TERMINATED AFTER CLRING THE RWY AND PAXS DEPLANED AT THE GATE. CONSTANT INTERPHONE COM BTWN CABIN AND COCKPIT CREW PROMOTED THE QUICK AND ORDERLY HANDLING OF AN UNCOMFORTABLE SITUATION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO. THE POST FLT INSPECTION SHOWED A PROBLEM WITH THE ACFT'S AIR CYCLE MACHINE AIR CONDITIONING SYS. RPTR STATED THAT THE WATER SEPARATOR BAG HAD A MALFUNCTION CAUSING A MIGRATION OF MOISTURE THAT CREATED THE SMOKE. THE SMOKE WAS FROM AN OIL BASE BUT CREATED BY THE SURGE OF MOISTURE. 2 YRS AGO THE ACR HAD REDONE THEIR CHKLISTS AND 2 ITEMS THAT WERE STRESSED FOR THIS TYPE SITUATION WERE MAINTAINING INTERCOM COM AND A RAPID RETURN AND LAND MANEUVER. THIS FLC DID THAT.