What happened
On 8 August 2009, a Mooney M20F Executive, registration G-CEJN, was conducting a local VFR flight to verify the operation of the landing gear following recent maintenance. The pilot/owner had recently replaced and adjusted a landing gear limit switch. During the flight, the pilot successfully cycled the gear three times and confirmed that the landing gear was down and locked, with the warning horn functioning correctly.
Upon returning to Wellesbourne Mountford Airfield, the pilot performed a final landing check. While the cockpit indicators showed the gear was down and locked, the aircraft's nosewheel collapsed shortly after touchdown. The propeller struck the runway, causing the engine to stop. The aircraft slid approximately 100 metres along the runway centerline before rotating 90 degrees to the left. There were no injuries to the pilot.
The investigation
AAIB investigators and airfield staff examined the aircraft and found that all three landing gears had collapsed. While the gear selector was in the down position, the gear legs only partially extended under gravity. Manual extension attempts were unsuccessful, and the gear was eventually moved into position by applying physical force to the legs.
Technical examination revealed that a retraction link (part number 53001-013) within the nose landing gear downlock system had been installed upside down. This incorrect orientation caused mechanical interference, preventing the downlock mechanism from reaching its full overcentre position. This resulted in a "soft" lock that could not withstand the forces of landing. The investigation also noted that the maintenance manual and parts manual lacked sufficient guidance or diagrams regarding the correct orientation of this specific link or the placement of its grease nipples.
Findings
- The nose landing gear downlock mechanism failed to engage fully due to mechanical interference.
- The retraction link had been fitted upside down during recent maintenance.
- The incorrect installation prevented the downlock from reaching the overcentre position, leading to the collapse upon touchdown.
- Existing maintenance and parts manuals provided no specific guidance or visual aids for the correct orientation of the retraction link or its grease nipples.