What happened
On 10 October 2024, a Flight Design CTSW, registration G-CFFJ, was performing a private local flight from Carlisle Airport in Cumbria. During the takeoff roll, the aircraft passed over a joint in the paved runway surface, at which point the pilot noted a rattling sound coming from the left cabin door.
As the aircraft climbed through approximately 50 to 100 feet, the left cabin door suddenly swung open. The pilot reported intense turbulence within the cockpit and significant concern that the door might detach and strike the tailplane. In an attempt to manage the emergency, the pilot tried to close the door using both hands while simultaneously controlling the aircraft with his knees. During a second attempt to secure the door, the pilot was unable to move the locking lever fully into the closed position. This distraction led to an aerodynamic stall, characterized by the dropping of the right wing. The aircraft subsequently struck soft ground outside the airport perimeter fence, resulting in the destruction of the aircraft and one serious injury to the pilot.
The investigation
The AAIB examined the wreckage and the door mechanism, which utilizes a gas-spring assisted 'gull-wing' design with a three-pin latching system. Investigators identified significant wear on the latching pins where they meet the composite frame. This finding led to a broader survey of three other Flight Design CTSW and CTLS1 aircraft, all of which exhibited similar wear patterns. However, testing revealed that the force required to unlatch the door was sufficient to prevent uncommand to uncommand openings in those inspected aircraft.
Findings
- The primary cause of the door opening was that the left cabin door was not fully latched closed before takeoff.
- Vibrations experienced during the takeoff roll, specifically when traversing runway joints, likely caused the unlatched lever to move, allowing the pins to disengage.
- Once the latch failed, the combination of the door's gas spring and aerodynamic loads caused the door to open rapidly.
- The pilot's attempt to secure the door while flying created a hazardous situation that led to the loss of control and subsequent stall.