What happened
On 10 March 2004, a Beech 76 Duchess, registration G-CBBF, was completing a private flight from Haverfordwest to Bournemouth Airport. The weather conditions were favorable, with a cloud base of 3,500 feet and a 13-knot wind from 030°. During the approach, the pilot confirmed the landing gear was extended and locked.
While on final approach, the pilot utilized two stages of flap and managed a slight crab to compensate for the left crosswind. The aircraft touched down near the runway centerline on both main wheels. However, shortly after touchdown, the right wing began to drop, causing the right propeller to strike the runway surface. Despite the pilot's attempts to correct the wing drop with full left aileron, the aircraft's airspeed decreased, leading to a further drop of the right wing. The aircraft veered to the right, eventually coming to a halt on the grass after a turn of more than 90°. There were no injuries to the two crew members on board.
The investigation
Following the incident, the aircraft was inspected, revealing that the right main landing gear leg had folded upward, while the other two legs remained locked. The investigation focused on the hydraulic landing gear system, which uses an electrically-driven pump to provide pressure to the actuators.
Upon further examination in a hangar, investigators identified a significant internal leak within the nose landing gear actuator. This leak allowed fluid to bypass between the extend and retract sides of the piston. Additionally, a dimensional inspection of the landing gear components revealed that the right landing gear's overcentre travel was slightly below the manufacturer's minimum requirements. This specific measurement is not included in the standard routine inspection schedule for this aircraft type.
Findings
- The right main landing gear leg failed to maintain its locked position during the landing roll.
- A crosswind during the landing run likely applied a side load to the right gear, causing it to move out of its overcentre position.
- An internal leak in the nose landing gear actuator prevented the hydraulic pump from generating enough pressure to re-extend and lock the right gear leg once the downlock microswitch was triggered.