What happened
On 9 October 2005, a Cessna 152, registration G-BGIB, was conducting a private flight near the Arlington Reservoir in East Sussex. The flight was a planned training session designed to practice engine-out procedures. During the exercise, the student pilot was practicing glide descents and en-route checks.
As part of the drill, the carburettor heat was set to the 'HOT' position. During a descent, the engine power was reduced to idle and then increased twice to warm the engine, while the carburettor heat remained active. Upon attempting a full power climb at 80 and 2,000 ft, the engine failed to respond to throttle inputs. The instructor took control, shut down the engine, and prepared for a forced landing.
While attempting to land in a sloping field, the aircraft travelled approximately 200 metres before the instructor applied heavy braking. This action caused the nose landing gear to collapse, resulting in the aircraft tipping onto its nose. There were no injuries to the two occupants.
The investigation
Investigators examined the aircraft's maintenance history and the physical condition of the induction system. The engine was equipped with a carburettor air box that utilizes a flexible hose to draw warm air from the exhaust system when carburettor heat is applied.
An inspection of the flexible hose revealed a split extending roughly two-thirds of its circumference. This specific hose was a double-ply 'Sceet' type rather than the single-ply 'Scat' type specified for the installation. Maintenance records indicated that the installation had been subject to chafing around the metal clamp.
Findings
- The engine failure was caused by carburettor icing.
- A split in the flexible air hose allowed colder air from the engine bay to enter the carburettor, increasing the risk of ice build-up.
- The weather conditions at the time were conducive to the formation of ice in the induction system.
- The use of a non-specified, double-ply hose may have contributed to the development of the split through chafing.