What happened
On 5 May 2008, a DH60G Gipsy Moth, registration G-ABDA, was conducting a private flight near Perth Aerodrome in Perthshire. The flight was intended to be a short trip to Strathallan, with an experienced pilot flying from the front cockpit to allow the owner to gain experience in the rear seat. After a delay to allow morning mist to clear, the aircraft taxied to the holding point for Runway 09.
The takeoff and initial climb proceeded normally. However, at an altitude of approximately 300 feet, the pilot noticed the engine was running roughly and power was decreasing despite the application of full throttle. The pilot requested the occupant in the rear cockpit to verify the position of the carburettor air heat control. Shortly after, between 300 and 400 feet, the engine continued to lose power and the aircraft began to descend. To avoid houses and power lines, the pilot turned the aircraft 30 degrees to the left and prepared for a forced landing in a field of standing oilseed rape.
The landing was executed in a three-point attitude. While the initial run was stable, the left wheel struck a deep furrow in the crop, causing the aircraft to yaw left. The landing gear collapsed, the engine detached from the fuselage, the propeller broke, and the leading edge of the wings and the fuel tank sustained damage. Both occupants escaped the DH60G Gipsy Moth uninjured.
The investigation
The investigation examined the aircraft's engine and the environmental conditions at the time of the accident. The engine showed no obvious signs of mechanical failure upon initial inspection. Investigators noted that the aircraft had been parked in a hangar overnight and the engine was started on a grass apron. The weather at the time featured high humidity, with wet surfaces in the parking area and along the taxi route, and a surface temperature of 20°C.
Findings
- The engine power loss occurred during the initial climb phase.
- The aircraft was not fitted with wheel brakes, which influenced the taxi and takeoff procedures.
- Carburettor icing is considered a potential cause of the engine power loss, as the high humidity and wet surfaces were indicative of conditions conducive to ice formation.
- The pilot reported that the carburettor air heat control remained in the OFF position throughout the flight.
- A contributing factor was the manual configuration of the heat control, which was only accessible to the occupant in the rear cockpit. The pilot's familiarity with aircraft featuring automatic systems may have contributed to the failure to use the manual heat control as a diagnostic tool.