What was found
WHILE CLIMBING OUT AND APPROXIMATELY 1000 FEET AGL, A PASSENGER REPORTED SMOKE IN THE CABIN TO THE FLIGHT CREW. FLIGHT CREW CONFIRMED WHAT TO BE SMOKE. AN-IN FLIGHT EMERGENCY WAS DECLARED AND THE CREW RETURNED TO THE AIRFIELD. FIRE CREWS WERE REQUESTED AND AN UNEVENTFUL LANDING WAS ACCOMPLISHED. MAINTENANCE WAS CONTRACTED TO INSPECT AND REPAIR THE AIRCRAFT. TECHNICIANS DETERMINED THE AIR CYCLE MACHINE (ACM) HAD SEIZED. A REPAIRED ACM WAS INSTALLED, OPERATIONALLY CHECKED SATISFACTORILY AND THE AIRCRAFT SUBSEQUENTLY RETURNED TO SERVICE.