What happened
On 5 September 2003, a Cessna F177RG Cardinal, registration G-BFIV, was conducting a private flight from Blackbushe Airport to Henstridge Airfield. During the downwind leg at Henstridge, the pilot attempted to extend the landing gear, but a mechanical noise was heard from the rear of the aircraft. While the nose gear successfully locked, the main gear remained partially extended, trailing in the slipstream.
Despite attempts to rectify the situation by cycling the gear and using the emergency hydraulic hand pump, the main gear failed to lock. The pilot decided to return to Blackbus and, after being unable to secure landing permission at Wycombe Air Park, prepared for an emergency landing on the Blackbushe runway. To minimize the risk of propeller or engine damage, the pilot chose to land on the aircraft's belly with the nose gear retracted. The aircraft touched down and slid to a stop without fire or significant injury to the two occupants.
The investigation
Investigators examined the aircraft and found that the main gear could be manually pulled into the locked position. A detailed inspection of the landing gear system revealed that the hydraulic actuator rod end had failed, severing the connection between the actuator and the main gear.
Metallurgical analysis of the failed rod end showed that the component had fractured at the greasing hole. The investigation determined that the strength of the rod end had been compromised by machining errors during the creation of the hole, which likely led to a high-stress fatigue mechanism.
Findings
- The main landing gear failed to lock because the actuator rod end had fractured.
- The failure was likely caused by stress concentrations and machining abuse at the greasing hole of the rod end.
- The aircraft was still fitted with an older, lower-strength version of the rod end.
- A manufacturer service letter issued in 1979 had recommended replacing these older parts with a higher-strength version that eliminated the greasing hole to avoid such failures.