A JETSTREAM 3100 ON TXWY PRIOR TO TKOF DECLARED AN EMER AND EVACED THE ACFT DUE TO SMOKE IN THE PAX CABIN CAUSED BY A SEPARATED AIR CONDITIONING DUCT.

Narrative

ACFT ZZY WAS TAXIED OUT OF THE GATE AT XA11 LCL ON A FLT FROM IAD TO JFK. THE ACFT DEPARTED THE GATE AND WAS CLRED TO TAXI TO RWY 19R. DURING THE TAXI TO RWY 19R ALL TAXI CHKS WITH THE EXCEPTION OF THE TTL CHK HAD BEEN ACCOMPLISHED. WHILE HOLDING BEHIND SEVERAL ACFT FOR RWY 19R; THE TTL CHK WAS COMPLETED. WHILE WAITING FOR SEVERAL ACFT TO ARRIVE AND DEPART; MY FO LOOKED BACK TOWARDS THE PAX CABIN AREA. HE IMMEDIATELY NOTIFIED ME THAT HE SAW SMOKE IN THE CABIN BY SEAT 1A AND 2A. I TURNED AND SAW SMOKE EMITTING FROM THE OVERHEAD LIGHTING PANEL OF SEAT 1A. THE ACFT WAS TAXIED INTO THE RUN-UP BLOCK OF RWY 19R. THE ACFT WAS BROUGHT TO A STOP AND AN EMER EVAC WAS EXECUTED AND SAFELY COMPLETED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ACFT WAS EVACED ON THE BASIS OF VISIBLE SMOKE OBSERVED IN THE PAX CABIN BY THE FO. THE RPTR SAID IT LATER WAS DISCOVERED AN OVERHEAD AIR CONDITIONING DUCT HAD SEPARATED ALLOWING COOL MOIST AIR FOG TO FLOW AROUND THE OVERHEAD LIGHTING PANELS. THE RPTR SAID THE ACTIONS OF THE CREW IN THIS INCIDENT WERE CRITICIZED BY THE COMPANY MGMNT FOR NOT LEAVING THE COCKPIT AND CHKING THE RPTED SMOKE OR CONDENSED AIR.