What happened
On 16 June 2019, a Cessna F177RG Cardinal RG, registration G-AYSY, departed Leicester Airport for a short flight to Sywell Aerodrome. During the flight, the pilot observed that the landing gear was taking significantly longer than usual to retract. Upon arriving at Sywell, the pilot attempted to extend the gear, but neither the green down-and-locked nor the red up indicator lights were illuminated.
Following a go-around and an attempt to use the emergency hand pump—which proved ineffective due to a lack of hydraulic pressure—the pilot decided to return to Leicester Airport. The pilot chose this location due to familiarity and the availability of a smooth grass runway. During a low approach at Leicester, ground observers noted the gear was hanging down but not locked. As the pilot approached the grass runway, the engine was shut down at approximately 100 ft. While the touchdown was initially smooth, the propeller and exhaust system subsequently struck the ground, causing the aircraft to stop abruptly. The pilot sustained minor injuries.
The investigation
The investigation focused on the failure of the hydraulic system to lock the gear in the down position. Examination of the aircraft revealed that the hydraulic landing gear-up pressure line had detached from its fitting. This separation allowed the hydraulic fluid to escape the system entirely.
It was noted that the aircraft had recently undergone maintenance to address a separate issue regarding hydraulic pressure loss. While the system had been tested successfully 18 times following those repairs, the investigation looked into the integrity of the aluminium flare fittings used in the hydraulic lines. The investigation also confirmed that the emergency hand pump was unable to function because the loss of fluid rendered the manual system useless.
Findings
- The separation of the hydraulic pressure line at the flare fitting caused a total loss of hydraulic fluid.
- Because the fluid escaped, the landing gear could not reach the over-centre lock position, preventing the hydraulic pump from switching off and leading to continuous fluid depletion.
- The aluminium tubing used in the system is thin-walled and susceptible to failure at the flare joints due to factors such as age, repeated movement, or overtightening.
- The pilot's decision to land on a grass strip was a calculated attempt to mitigate the risks of an unverified gear position.