What happened
On 9 February 2004, a Cessna 1s77RG Cardinal, registration G-TOTO, was performing a private flight to Meppershall Airfield for maintenance purposes. The aircraft had recently experienced issues with the landing gear failing to retract fully. For this specific flight, the landing gear was kept in the extended position, and the circuit breaker for the electric hydraulic pump had been pulled.
The landing at the grass airfield was initially described as very smooth. However, as the aircraft decelerated after touchdown, the nose wheel dropped, causing the propeller to strike the ground. The impact resulted in an engine shock load and damage to the propeller, the nose landing gear doors, and the exhaust pipe. There were no injuries to the pilot.
The investigation
The AAIB investigation focused on the mechanical state of the landing gear system. Post-accident inspections revealed that the nose landing gear overcentre downlock was significantly out of adjustment, meaning the force required to unlock it was minimal. Furthermore, the investigation found that the left main landing gear downlock latch pivot pin had failed due to a double fatigue mechanism. The right main landing gear downlock latch pivot pin was also found to be at the point of imminent failure due to a similar fatigue pattern.
It was determined that the recent difficulties with the gear failing to retract were likely caused by the failure of the left main landing gear pivot pin, which prevented the unlock solenoid from pivoting correctly. The investigation also noted that the aircraft's landing gear had been subject to various maintenance and replacements in recent years, including a replacement of the right main landing gear assembly in 2002.
Findings
- The nose landing gear collapse was caused by a combination of an out-of-adjustment overcentre downlock and the lack of hydraulic pressure in the down lines, as the hydraulic pump could not activate due to the pulled circuit breaker.
- Undulations on the grass runway may have caused oscillations in the nose gear oleo, triggering the improperly adjusted downlock to move into the unlock position.
- The failure of the main landing gear downlock latch pivot pins was caused by fatigue resulting from either incorrect rigging or excessive loads from previous heavy landings.
Safety action
- It was recommended that Cessna maintenance documentation should instruct operators to examine the corresponding main landing gear assembly whenever a mechanical failure is found in any part of the assembly.
- A recommendation was made to consider making a Service Kit available to upgrade the landing gear extension/retraction system to the newer standard used in later aircraft models.