What happened
On 1 June 2024, a Beechcraft King Air C90GTx, registration D-IMEP, was conducting a private flight from London Biggin Hill Airport. Shortly after departing the airfield, as the aircraft climbed through 1,700 ft amsl, the pilot observed the red cabin door warning annunciator flickering before it remained steadily illuminated. At the same moment, an audible bang was heard in the cockpit, which the pilot believed indicated the cabin door had opened.
The pilot immediately declared a PAN-PAN to Air Traffic Control and initiated an emergency return to the airport. The aircraft landed safely with no injuries to the pilot and no damage to the crew. The incident resulted in damage to the passenger cabin door assembly.
The investigation
The AAIB investigation examined the aircraft's door locking mechanism and reviewed airport security footage. CCTV from the airport apron, reviewed by the airport manager, indicated that the external door handle appeared to be in the closed position prior to departure.
Investigators noted that the Pilot Operating Handbook and standard checklists require several visual and mechanical checks to confirm the door is properly secured before flight. The aircraft manufacturer also noted that this specific type of event is rare, with only two other recorded instances of the cabin door opening inadvertently during flight in the King Air 90 series.