What happened
On 7 August 2002, a Piper PA-28-140 Cherokee, registration G-AYWE, was conducting a PPL skill test near Denham Airfield. During the flight, the crew performed regular checks for carburettor ice with no issues noted. After a successful touch-and-go on Runway 24, the aircraft prepared for a subsequent circuit involving a glide approach.
During the downwind leg, the student pilot applied full carburettor heat for several seconds as part of the pre-landing checks. On the base leg, the heat was applied again before the throttle was closed for the descent. As the aircraft descended from 750 feet, the engine speed dropped to between 1,100 and 1,200 RPM. Following the deployment of 25° flaps, the aircraft began to undershoot the aiming point.
At approximately 200 feet above the ground, the instructor requested an application of power. Although the student reacted immediately by applying full throttle, the engine failed to respond. Despite switching the carburettor heat to the 'cold' position, the power loss persisted. The aircraft subsequently struck trees in the undershoot area and impacted the ground roughly 100 metres short of the runway threshold. The impact caused severe damage to the aircraft, including the loss of the left wing and all landing gear, but the crew escaped the wreckage without assistance and no fire occurred.
The investigation
The AAIB examined the aircraft and engine at Denham Airfield. While the impact caused significant structural damage to the fuselage and landing gear, the cabin remained intact. The investigation focused on determining if a mechanical failure caused the engine's lack of response to the throttle.
Engine inspections revealed that the induction paths were clear and the throttle and mixture controls were functional. The carburettor heat control was found to be jammed due to impact damage, but investigators determined the heat flap was in the 'cold' position at the time of the accident. The carburettor was disassembled at Farnborough, and tests on the inlet filter, main jet, accelerator pump, and electric fuel pump showed no defects. Furthermore, the fuel was confirmed to be correct and free of water. No mechanical defect was found to explain the engine's failure to respond to power.
Findings
- The engine failed to respond to full throttle application during the final approach.
- Weather conditions, characterized by heavy showers and high humidity, were highly conducive to carburettor icing.
- There was no evidence of any mechanical malfunction in the engine, fuel system, or induction system prior to the impact.