What happened
On 31 October 2005, a Cessna 210M Centurion, registration G-TOTN, was conducting a short positioning flight to Top Farm when the pilot encountered a failure in the landing gear deployment mechanism. The pilot was unable to extend the landing gear using either the standard control selection or the manual emergency pump.
Upon observing the gear doors had opened via a wing-mounted mirror, the pilot decided to divert to Cambridge City Airport. The aircraft performed a successful gear-up landing, which resulted in damage to the propeller and the underside of the fuselage. No injuries were reported following the incident.
The investigation
Investigators examined the aircraft's maintenance history and found that the landing gear had undergone recent servicing, which included the installation of a new squat switch on the nose gear actuator on 17 October 2005.
During ground testing at a maintenance facility, engineers discovered that when the gear down switch was activated, the nose gear would partially deploy and then immediately begin to retract. This cycle of partial retraction and deployment continued until the gear up selection was made. Further technical analysis of the hydraulic and electrical schematics revealed that the only way to achieve full deployment in this specific failure state was to shut off all electrical power and utilize the hand pump. The pilot's actions were found to be consistent with the procedures outlined in the Pilot’s Operating Handbook.
Findings
- The failure to deploy the landing gear was caused by incorrectly installed wiring for the nose landing gear squat switch.
- The two wires from the squat switch had been routed improperly, causing the spiral protective wrap to be damaged and the wire cores to be exposed.
- When the nose gear was partially deployed, the damaged wiring created an earth, which energized the gear up solenoid and triggered the retraction cycle.
- The pilot followed the correct emergency procedures as documented in the aircraft manual.