What happened
On 11 April 2005, a Rockwell Commander 112, registration G-DASH, was completing a private flight from St Mawgan to Bourn Airfield. Following a standard landing on Runway 2 landing on Runway 24, the pilot confirmed that the landing gear was down and locked via three green cockpit indications. The initial ground roll proceeded normally; however, as the aircraft slowed to a ground speed of roughly 10 knots, the pilot applied light braking. At this moment, the nose landing gear partially collapsed, causing the propeller to strike the runway surface and resulting in the engine stopping. There were no injuries to the pilot or the passenger, though the aircraft sustained damage to the engine nacelle, propeller, and nose landing gear leg.
The investigation
The investigation examined the hydraulic and electrical systems responsible for the aircraft's retractable tricycle landing gear. The system utilizes a hydraulic pump and a selector switch to move the gear, with mechanical locks and a drag brace to secure the legs in the down position. A squat switch on the right main gear leg is designed to prevent retraction while the aircraft is on the ground.
Investigators identified an intermittent earth connection within the electrical circuit for the nose leg down-lock position switch. While this fault was present, it was noted that such a fault would typically affect the gear-down circuit rather than causing retraction. Maintenance checks and retraction tests performed on both the original and replacement nose gear legs revealed no other mechanical or hydraulic failures in the system.
Findings
- The aircraft encountered several rough patches on the runway surface during the landing roll.
- Although the pilot did not recall moving the gear selector to the 'UP' position, the investigation considered the possibility that the switch was inadvertently moved after landing.
- An intermittent earth connection in the nose-down-lock position switch meant that if the gear had begun to retract due to the selector switch movement and the squat switch closing, the pilot would have been unable to re-engage the hydraulic pump to lock the gear back down.
- If the nose gear began retracting while the main gear remained locked, the weight of the aircraft would cause the nose leg to collapse as it encountered runway irregularities.