Incident
On 10 July 1998 at 1713 UTC, a Cessna F177RG (registration G-AYSY) departed from Woodford on a private flight to Meppershall, Bedfordshire. Shortly after takeoff, the pilot noted that the electro-hydraulically operated landing gear had not retracted normally after selection, and neither the red nor green indication lights illuminated, indicating the gear could not be locked down. In accordance with the aircraft's Operating Handbook, the pilot attempted to extend the gear using the hand pump, but even after prolonged pumping, there was no resistance. Throughout the flight, further attempts to fully extend the landing gear were unsuccessful.
Realizing a landing without the gear locked down was inevitable, the pilot declared an emergency with East Midlands Approach. After discussing possible landing sites, including Leicester and Henlow, the pilot chose Cranfield Airfield due to the availability of a grass runway and the Airfield Fire Service (AFS). Following an overflight and a simulated approach for the benefit of the AFS, the pilot shut down the engine, fuel, and electrical systems before touchdown. The aircraft was landed on the grass just to the right of disused Runway 26. During the landing, the nose gear remained extended, but both main gear legs collapsed rearwards, causing minor damage to the underside of the fuselage and the stabilator. The pilot, who was uninjured, vacated the aircraft, and the AFS disconnected the battery.
Background
Approximately 10 flying hours before this incident, the low voltage warning light had been illuminating intermittently, in time with the strobe lights. An investigation at that time concluded that a faulty pressure switch in the landing gear hydraulic pump was causing the pump to run continuously after gear retraction, thereby draining system voltage. As a result, the pump and pressure switch were replaced.
Investigation
Following the landing at Cranfield, examination of the aircraft by the organization responsible for its maintenance revealed that the hydraulic system was empty of fluid. After the system was replenished and functioned, a fluid leak was observed at a flared pipe connection immediately downstream of the pump. Close examination showed a crack in the flared end of the pipe, which had caused the complete loss of fluid. It was therefore evident that this leak had prevented the pressure switch from sensing the normal rise in hydraulic pressure that should occur after gear retraction, causing the pump to continue to run for an extended period, as evidenced by the state of wear of the associated electric motor.