What was found
(CAN) AFTER TAKEOFF CALGARY (CYYC), CLIMBING THROUGH 14,000 FEET, THE CREW AND PASSENGERS HEARD A LOUD BANG, THEN THE CABIN AIRSTAIR DOOR DROPPED OPEN. THE CREW DECLARED AN EMERGENCY TO ATC, INSTITUTED AN EMERGENCY DESCENT AND TURNED BACK FOR CALGARY WHERE THEY LANDED WITHOUT FURTHER INCIDENT. THE CAUSE OF THIS DOOR FAILURE IS NOT FULLY KNOWN AT THIS TIME, BUT IT DOES APPEAR THAT THE FORWARD UPPER LATCH HOOK ASSEMBLY FAILED. REPORTS ON THE EXACT CAUSE WILL FOLLOW AFTER INVESTIGATION.