Summary
On 13 August 2002, a Cessna 210 Centurion, registration EI-CGH, operated on a private flight, experienced a landing gear malfunction during a return to Belfast Aldergrove. The aircraft touched down with its landing gear not locked down, resulting in a belly landing. The pilot, the sole occupant, was uninjured. Damage was superficial to the aircraft's underside and propeller.
History of Flight
The aircraft had been flown to Belfast for an avionics check by a maintenance organisation. After the checks, the pilot refuelled and departed for the return flight to his home airfield. Shortly after takeoff, the pilot observed an electrical problem and the autopilot was not functioning. He requested and was cleared to return to Aldergrove to consult the maintenance organisation.
On approach, the pilot selected 10° of flap and lowered the landing gear. He believed he saw the green landing gear indicator light. Late in the approach, he glanced out of the left side window and saw the left main landing gear wheel. He closed the throttle and touched down softly, but the aircraft's belly contacted the runway almost immediately. The aircraft slid to a stop within about 50 yards. No landing gear warning horn sounded when the throttle was retarded. The pilot exited the aircraft unassisted.
Examination and Testing
Examination after recovery showed that the landing gear was not locked down but was hanging in the airstream at touchdown, with the gear selector in the DOWN position. The hydraulic pump motor circuit breaker had tripped, disabling hydraulic pressure to the landing gear system. The indication system circuit breaker was still made and functioning.
Tests revealed that the pressure switch activated the pump at 1,200 psi but malfunctioned, failing to open the circuit when pressure reached 1,500 psi. As a result, the pump motor continued running until the pressure reached 1,800 psi, at which point the pressure relief valve opened. The sustained high current demand caused the circuit breaker to trip approximately 18 seconds after the gear reached its limit position. This behaviour was observed repeatedly.
The landing gear warning horn was checked; the throttle had to be retarded almost to the idle stop before the horn sounded. The propeller strike during the landing may have altered the horn microswitch setting. The correct horn microswitch position must be set in flight. The cause of the autopilot failure was not determined.
Discussion
The pilot stated that he believed he had selected the landing gear DOWN, and the positions of the selector and the landing gear after the landing supported this. Because the gear selector is a hydraulic changeover valve, selecting DOWN would have released the gear from the up position, where it was held by locked-in hydraulic pressure. However, with the hydraulic pump motor circuit breaker tripped, the system could not pressurise, and the main landing gear legs trailed in the airstream. It is almost certain that the left main wheel was far enough forward to be visible from the cockpit. The nose landing gear likely did not lock without hydraulic pressure. With the gear partially extended, the indicator system would show no lights, consistent with the pilot seeing no green light.