History of the Flight
The aircraft, a Cessna 210M Centurion registered G-TOTN, was on a short positioning flight on 31 October 2005. According to the pilot's report, he was unable to deploy the landing gear using either the normal control selection or the manual pump. He observed through the wing-mounted mirror that the landing gear doors had opened successfully.
The pilot elected to divert to Cambridge City Airport, where visibility was 10 km with a 4 kt wind and no significant weather. He performed a successful gear-up landing, sustaining damage to the propeller and the underside of the fuselage. No injuries were sustained, and the pilot noted that ATC and fire services were supportive.
Engineering Investigation
The landing gear had undergone recent maintenance, including the replacement of the squat switch on the nose gear actuator, documented on 17 October 2005. After the incident, the aircraft was taken to a maintenance facility at Cambridge City Airport and jacked for inspection.
When engineers attempted to deploy the gear using the gear-down switch, the nose gear partially deployed and then began to retract. The nose gear became trapped in a cycle of partial retraction and deployment, which continued until gear-up was selected.
Further inspection revealed that the two wires from the squat switch had been incorrectly routed and had become trapped in the nose gear down-lock hook. The spiral wrap protecting the wires was damaged, and the wires were squashed, exposing the cores. After the damaged wires were replaced, the gear functioned satisfactorily.
A review of the wiring diagram indicated that if either of the two wires from the squat switch contacted earth, it would energize the gear-up solenoid, causing the gear to retract. The evidence suggested that the incorrectly routed, damaged wiring was creating an earth when the nose gear was partially deployed, causing the gear to become stuck in a cycle of partial retraction and deployment when gear-down was selected.
Further analysis of the hydraulic and electric system schematic showed that the relevant circuit breaker would not have tripped in this situation and could not be manually tripped. The only way the pilot could have deployed the gear was by switching off all electrics and using the hand pump. The Pilot's Operating Handbook did not contain a specific procedure for this scenario, and the pilot acted in accordance with the Handbook.