What happened
On 1 December 2004, a Socata TB20 Trinidad, registration G-HGPI, was returning to Bournemouth International Airport following a cross-country flight from Cherbourg, France. During the approach, the pilot attempted to extend the landing gear but observed that only the nose gear indicator showed a 'down and locked' status. Subsequent attempts to cycle the gear through the normal selector and the emergency extension knob failed to lock the main gear.
After notifying the control tower, the pilot performed a low fly-by, during which the tower controller noted that the main gear appeared to be extended. The pilot proceeded with a standard right-hand circuit to land on Runway 08. Upon touchdown, the right main gear leg collapsed, causing the right wing tip to strike the runway surface. The aircraft sustained damage to the underside, the right wing, and the stabilator. There were no injuries to the two occupants.
The investigation
Investigators examined the aircraft's hydraulic landing gear system, which relies on an electro-hydraulic generator to actuate the gear and microswitches to confirm the locked position. During inspections performed on jacks, it was discovered that the hinged struts for both the left and right main gear were stiff. While the electro-hydraulic generator appeared weak, no specific internal fault was identified during its strip-down.
Maintenance records showed that a 50-hour check had been completed in September 2004, during which the gear systems were tested successfully and the struts were lubricated. However, the aircraft was stored outdoors under a cover rather than in a hangar. Following the accident, the main gear hinged struts were removed, treated for corrosion, and lubricable, which restored normal operation.
Findings
- The primary cause of the failure was the stiffness of the main gear hinged struts, which prevented the gear from locking into place.
- Corrosion and stiffness in the hinges likely developed due to the aircraft being parked outside, exposing the components to environmental elements.
- Although the gear had been lubricated during a recent maintenance check, the lack of frequent use and exposure to rain contributed to the deterioration of the hinge movement.