Incident
On 30 May 2020 at 1255 UTC, a Mooney M20K (registration G-OSUS) departed from Charlton Park Airstrip on a private flight with one pilot and one passenger. Approximately 15 minutes into the flight, while passing overhead Membury Airfield, Berkshire, the baggage door opened and detached. The door struck and became lodged on the right tailplane leading edge. The pilot experienced pitch and roll control difficulties, declared a MAYDAY, and executed an emergency landing on Runway 13 at Membury Airfield. The landing was successful with no injuries to crew or passengers, though the aircraft sustained damage to the baggage door, rear fuselage, and tailplane.
Aircraft Information
The Mooney M20K is a single-engine, four-seat light aircraft. It is fitted with a baggage door that is hinged at the top and secured at the bottom by two shoot bolts, which extend into the door frame when the operating handle is closed. The door also serves as an auxiliary exit and is equipped with an internal emergency handle, which can open the door even if the external handle is locked. A secondary locking clip, introduced via Service Bulletin SB M20-239A and mandated by Airworthiness Directive AD 88-25-11, is designed to prevent inadvertent operation of the internal emergency handle.
Investigation
Examination of the aircraft revealed that the baggage door’s internal emergency handle was partially open before the flight, as seen in a photograph taken at Charlton Park. The handle was found to have its secondary locking clip installed under the handle rather than over it, so it did not provide a locking feature. The clip was also bent, suggesting the handle had been forced down onto it. Additionally, the clevis pin was loose in its mounting plate, making correct installation of the clip impossible without lifting the pin.
During the flight, it was likely that the handle moved further toward the open position, sufficient to disengage the shoot bolts from the door frame, allowing the door to open. The force of the airflow then detached the door. It could not be determined when the internal handle and safety clip were incorrectly installed. The aircraft had been repainted in 2019, during which the trim panel was removed and refitted, and had undergone an annual inspection and airworthiness review on 29 May 2020 that included an operational check of door latching and locking. The pilot had not touched the internal handle since the recent maintenance and had checked the door closure externally and visually from the cockpit before departure.
Conclusion
The safety clip for the internal operating handle of the baggage door was not correctly installed, so instead of holding the handle closed it held it slightly towards the open position. During flight it seems most likely that this handle moved further open, and sufficiently far to disengage the shoot bolts from the door frame, allowing the door to open. The force of the airflow then detached the door and it struck and became jammed on the tailplane. It could not be determined when the internal handle and its safety clip were incorrectly installed or why.