What happened
On 21 January 2007, a Cessna 401, registration N401JN, was performing a private flight that concluded with an ILS approach and landing on Runway 2B at Blackpool Airport. The weather conditions involved a wind from 250° at 24 knots. Following a normal landing, the aircraft was in the process of the landing rollout when the right main landing gear suddenly collapsed. The aircraft travelled approximately 100 metres short of taxiway Charlie, resulting in damage to the right wing, the right engine propeller, and the right landing gear and flaps. The two crew members on board exited the aircraft without injury.
The investigation
Investigators examined the aircraft's landing gear mechanism, specifically the electrical extension and retraction system. They found that the failure of the arm attachment holes on the right main landing gear torque tube had caused the pushrod from the electrical actuator to disconnect. A detailed metallurgical examination of the removed torque tube revealed a slow, progressive fatigue failure that was subsequently followed by a rapid overload. Analysis of the fatigue crack striations indicated that the crack had been present for approximately 250 cycles, which corresponded to a period dating back to roughly May 2001.
Findings
- The right main landing gear collapsed because the arm attachment holes on the torque tube failed.
- The failure was caused by an initial fatigue crack followed by a rapid overload.
- The fatigue crack had been growing for approximately 250 landing cycles, likely since May 2001.
- The fracture likely occurred during the extension of the gear for landing, leading to a side load that caused the collapse.
- While a Cessna Supplemental Inspection Document (SID) issued in 2004 recommended inspections of these holes, the requirement was not mandatory for US-registered aircraft like N401JN at the time of the accident.
Safety action
- A safety recommendation was made to the Federal Aviation Administration (FAA) to mandate the Cessna SID 32-10-05 for the Cessna 401/402 main landing gear torque tube, along with similar SIDs for related torque tube designs.