What was found
FLIGHT CREW EXPERIENCED SMOKE IN THE CABIN/COCKPIT WHILE IN FLIGHT. CREW DONNED THEIR O2 MASKS, DECLARED AN EMERGENCY AND DIVERTED TO TNCM. THE AIR SOURCE WAS SELECTED TO THE OFF POSITION, AND THE SMOKE SLOWLY DISSIPATED. AN UNEVENTFUL LANDING WAS ACCOMPLISHED AT TNCM. MAINTENANCE FOUND THE AIR CYCLE MACHINE HAD FAILED P/N: 3471A020000 S/N: 00444. ACM WAS REPLACED WITH A REPAIRED UNIT; LEAK AND OPERATIONAL CHECKS WERE NORMAL. AIRCRAFT WAS RETURNED TO SERVICE.