What happened
On 2 November 2007, a student pilot was conducting a solo navigation exercise in a Reims Cessna F152 Aerobat, registration G-BFZT. During the flight, the engine began running increasingly roughly. The pilot attempted to rectify the issue by applying carburettor heat and subsequently returning the control to the cold setting, but the engine performance continued to degrade as the use of the heat became less effective.
After initially attempting to find a turning point and deciding to return to Shobdon Airfield, the pilot opted to perform a precautionary landing in a field. Upon approaching a chosen site, the pilot aborted the approach due to the presence of sheep. A subsequent approach was made to a different field, where the engine was shut down and all electrical and fuel systems were switched off prior to touchdown.
While the initial contact with the ground appeared normal, the aircraft decelerated rapidly. The nosewheel subsequently dug into the soft earth and broke off, causing the aircraft to pitch forward and overturn onto its back. The pilot, who was wearing a four-point harness, sustained minor injuries and was able to exit the aircraft through the passenger window. A passing motorist alerted emergency services.
The investigation
The investigation established that the engine issues were caused by carburettor icing. The investigation also examined the pilot's decision-making and the instructor's previous briefing. It was noted that the instructor had previously deemed the weather suitable for the flight because the student had been trained to manage icing. However, the investigation found that the student's method of returning the carburettor heat to the cold setting contributed to the worsening engine state.
Findings
- The primary cause of the engine malfunction was carburettor icing.
- The pilot's technique of returning the carburettor heat to the cold setting allowed ice to accumulate, making the heat less effective during subsequent applications.
- The nosewheel collapsed because the gear dug into the soft ground during the landing roll.
- The instructor's briefing did not sufficiently emphasize that carburettor heat should be maintained until the engine returns to normal operation.