History of the Flight
On 3 July 2005, the pilot of a Cessna 152 (registration G-IRAN) departed Andrewsfield Airfield, Essex, for a local private flight. Approximately 30 minutes into the flight, while returning to Andrewsfield and shortly after descending from 2,500 ft to 1,500 ft, the engine abruptly lost power. The pilot selected carburettor heat ON, checked that the mixture was rich and the magnetos were set to BOTH, then attempted to restart the engine without success.
Realising he was at low height, the pilot concentrated on executing a forced landing into a field containing standing wheat, which was about two feet high. Before touchdown, he held the aircraft just above the crops in an attempt to land at the correct speed and reduce the subsequent ground run. However, the main wheels became entangled in the crops, the nose wheel dropped and dug into the ground. The aircraft then flipped over and came to rest inverted, suffering extensive damage to the nose leg, engine frame, propeller, fin and left tailplane. The pilot vacated the aircraft through a door, having suffered no injuries. The local emergency services arrived quickly and offered assistance.
Weather Conditions
The Meteorological Office provided an aftercast for the area at the time of the accident. It indicated a slack, moist, west-south-westerly airflow with a slow-moving cold front over south-east England. Surface wind was 250°/5 kt, temperature 17.3°C, dew point 14.9°C, relative humidity 86%. At 1,000 ft, wind was 250°/5-10 kt, temperature 14.4°C, dew point 10.4°C, humidity 77%. At 2,000 ft, wind was 250°/10-15 kt, temperature 11.2°C, dew point 8.9°C, humidity 86%. Visibility was expected to be 15-30 km, with mainly broken strato-cumulus clouds at 2,500-3,000 ft. The pilot reported that the weather obtained from Andrewsfield indicated surface wind 280°/5 kt, visibility 24 km, broken cloud at 2,800 ft, temperature 17.6°C, and humidity 78%.
Engine Examination
The aircraft and its engine were inspected at the crash site by the maintenance organisation that usually serviced the aircraft. At the time of inspection, the carburettor heat control was fully in (providing no heating to the carburettor), the throttle was at idle, and the mixture was fully rich. The engine showed no signs of leakage, oil level was within limits, and there was no damage to any ignition components or control cables. The engine was subsequently sent to an independent maintenance organisation for further tests. It started without difficulty, had no defects, and produced power to within 5% of maximum, which were within the limits set by the testing organisation.
Carburettor Icing Information
The aftercast temperature and dew point for the time of the accident were plotted on the Carb Icing Chart in Safety Sense 14. They fell, at best, in the Moderate icing (cruise power)/Serious icing (descent power) area, and at worst, in the Serious icing (any power) area. The source notes that carburettor icing is not restricted to cold weather and can occur on warm days with high humidity, especially at low power settings. Flight tests have produced serious icing at descent power with ambient temperatures over 25°C and relative humidity as low as 30%.
Conclusion
The ambient meteorological conditions and the flight profile preceding the engine failure, together with the absence of any defect with the engine, suggest that carburettor icing was the most likely cause of the engine failure.