What happened
On 29 September 2001, a Gardan GY80-180, registration G-AWAC, was conducting a private flight from Dunkeswell Airfield in Devon toward Popham in Hampshire. Roughly 30 minutes into the flight, the pilot noted that the engine had begun running roughly. Due to the loss of power, the pilot opted to perform a precautionary landing at the nearby Compton Abbas Airfield.
To prepare for the arrival, the pilot began the process of extending the landing gear, which involves manually rotating a crank handle approximately 19 times. However, as the engine power continued to decline, the aircraft lost altitude rapidly. The pilot was unable to complete the gear extension before the aircraft reached 200 feet above ground level, at which point the magnetos were switched off. The aircraft subsequently made a heavy landing on Runway 26, resulting in damage to the landing gear and the propeller.
The investigation
The AAIB examined the fuel system and the sequence of fuel selections made prior to the incident. The aircraft featured two 80-litre wing tanks and a 40-litre auxiliary tank located under the rear seat. The pilot had initially selected the 'ALL' setting for fuel. After 15 minutes of flight, the selection was changed to 'REAR'. Approximately 15 minutes later, the engine issues began. Although the pilot attempted to rectify the situation by switching the fuel cock back to 'ALL', the engine performance did not recover.
Post-accident inspections by the maintenance organisation found no mechanical faults within the engine itself. Investigators concluded that the issue likely originated from the fuel supply.
Findings
- The engine roughness was likely caused by air entering the fuel supply line.
- It is believed the auxiliary rear fuel tank had run low on fuel, leading to air entrainment.
- While the pilot attempted to switch the fuel source back to the wing tanks, there was insufficient time to purge the air from the system before the landing was forced.