Incident Overview
Following takeoff, a flight attendant reported that the aft airstair was partially open. The flight engineer confirmed the airstair was open approximately 18 inches. Remedial actions were attempted but unsuccessful, leading to an unscheduled landing that was completed without further incident. As the aircraft turned onto the taxiway, the airstair made contact with the ground.
Investigation Findings
Examination revealed that before departure, a maintenance supervisor had placarded the aft airstair warning lights in the cockpit as "inoperative" and made a logbook entry stating "airstairs checked up and locked." The inspection disclosed that the plunger on the aft airstair bungee assembly was bound inside its housing due to corrosion and dirt inside the bushing through which the plunger slides.
Maintenance Procedures
The maintenance minimum equipment and dispatch procedure that was performed involved verifying that the uplatch mechanism engaged with the uplock rollers on the airstair. However, a non-valid Trans World Airlines (TWA) aircraft maintenance bulletin indicated that this process does not ensure the uplatch mechanism is locked, and that the soft surfaces must be in contact to verify the crank arms are locked over-center.