What happened
On 1 July 2003, a Cessna F152, registration G-BIJX, was conducting a training flight from Lydd to Headcorn Aerodrome. The flight crew, consisting of an instructor and a student pilot, intended to perform a touch-and-go landing on the grass runway at Headcorn. During the descent on the base leg, the student pilot applied carburettor heat and reduced power. At approximately 200 feet above the ground, the carburettor heat was switched to the cold setting.
Upon touchdown, the aircraft began its landing roll, and the instructor reduced the flaps to 10°. However, the aircraft failed to accelerate normally. Despite the instructor applying full power, the engine RPM remained at approximately 2,100, which was significantly lower than the expected range. Realising the aircraft would not gain enough speed to clear the hedge at the end of the runway, the instructor aborted the takeoff attempt, applying brakes and pulling the yoke aft. The aircraft failed to stop within the remaining runway length, running off the end of the grass strip and penetrating a hedge before coming to rest on a nearby road. There were no injuries to the two crew members.
The investigation
The investigation examined the engine, the aircraft's maintenance history, and the environmental conditions. The engine and carburettor were inspected by a maintenance organisation, and no mechanical faults were found that could explain the power loss. The investigation also reviewed the discrepancy between the Cessna 152 Information Manual and CAA advice regarding the use of carburettor heat during approach.
Atmospheric data indicated high humidity and recent heavy rain, creating conditions highly conducive to carburettor icing. The investigation also assessed the braking performance on the grass surface. While the aircraft had more than one-third of the runway remaining, the instructor noted the grass was short and wet, which likely contributed to the lack of effective braking.
Findings
- The engine experienced a significant reduction in thrust due to the RPM dropping from a normal level to approximately 2,100 RPM.
- Carburettor icing was considered the most likely cause of the reduced engine performance, as the high humidity and temperature conditions supported ice formation.
- The wet and short grass surface caused the aircraft to skid, significantly reducing the effectiveness of the brakes and leading to the runway overrun.
- There was a conflict between the aircraft's operating manual and CAA guidance regarding the timing of switching carburettor heat to the cold position during approach.