Incident Summary
After takeoff, at 800 feet above mean sea level, the forward airstair door opened. The flight crew declared an emergency and returned to the airport, where the aircraft landed without further incident. Inspection revealed damage to the propeller blades and the aft cables of the forward airstair door. The door latching mechanism was found to have operated normally.
Background
The forward cabin door annunciator light was inoperative and had been deferred under a Minimum Equipment List (MEL) procedure, with a scheduled examination for later that evening. Over the previous year, six discrepancies related to the forward airstair door annunciator had been recorded; the most recent occurred two days before the incident.
Prior to departure, the captain briefed the first officer (F/O) on the MEL item. The F/O reported closing and locking the forward airstair door and verifying that it was secured. The F/O then verbally briefed the passenger seated adjacent to the door on the door opening procedures but did not provide a demonstration. Company procedures for F/Os taught verbal discussion of the door opening procedure without demonstration. However, several company F/Os reported that they would partially open the forward airstair door to demonstrate the procedure to the passenger after closing and locking the door.
Post-Incident Findings
After the incident, the F/O was vague when asked about how to verify that the forward airstair door is locked. Drug screening tests for both the captain and the F/O returned negative results.