What was found
DURING CLIMB-OUT OF ANC AT 16000 FT, CREW HEARD LOUD BANG AND AIR RUSHING SOUND AS DOOR WARNING LIGHT ILLUMINATED AND CABIN ALTITUDE STARTED TO CLIMB RAPIDLY. CREW ACCOMPLISHED EMERGENCY DESCENT, RETURNED TO ANC AND LANDED WITHOUT INCIDENT. MAINTENANCE FOUND CREW DOOR, IN MAIN CARGO DOOR, LATCH TENSION HANDLE IN UNLATCHED POSITION ALLOWING DOOR TO OPEN APPROX .125 IN. INSPECTED DOOR FOR DAMAGE AND SEAL CONDITION, NO DEFECTS NOTED. SUSPECT LATCH TENSION HANDLE RETAINING CLIP NOT PROPERLY SECURED PRIOR TO FLIGHT.