What happened
On 2 April 2009, a Beech 76 Duchess, registration G-TWNN, was conducting a training flight at Bournemouth Airport. During a stalling exercise, the pilot lowered the landing gear, but only two of the three green 'down and locked' lights illuminated. The light for the right main landing gear failed to show, despite testing confirming the bulb was functional.
In an attempt to rectify the issue, the crew utilized the emergency gear extension system and performed vigorous manoeuvres to try and release the gear. However, the indication remained unchanged. After informing Air Traffic Control (ATC) of the situation, the aircraft flew past the control tower to allow controllers to visually verify the gear position. ATC confirmed the right main gear was not extended.
Following a review of the wheels-up landing checklist, the crew prepared for a landing. During the flare, both engines were shut down and the propellers were feathered. Upon touchdown on the left main wheel, the pilot attempted to keep the right wing elevated. Eventually, the wing tip made contact with the ground, causing the aircraft to swing to the right before stopping beside the runway. There were no injuries to the two crew members or the single passenger on board.
The investigation
The investigation focused on the hydraulic and mechanical operation of the landing gear. The aircraft's landing gear is powered by an electric motor-driven hydraulic system, featuring a trailing link design with an oleo shock absorber.
Upon disassembly of the right main landing gear strut, investigators discovered internal corrosion within the oleo. This corrosion had restricted the movement of the internal piston, preventing the strut from extending to its full length. It was determined that the strut was likely at only about three-quarters of its maximum extension following a previous takeoff. This shortened length caused the wheel to sit further aft than normal, resulting in the wheel fouling the edge of the wheel-well. While this positioning allowed the gear to retract, it prevented the gear from fully extending during the flight in question.
Findings
- The right main landing gear failed to extend due to the wheel fouling the edge of the wheel-well.
- Internal corrosion within the oleo strut had inhibited the free movement of the internal piston.
- The oleo strut was maintained on an 'on condition' basis, meaning it was not subject to periodic internal inspections.
- The maintenance organisation has since implemented a new procedure to check the range of travel for oleo struts during 150-hour inspections.