What happened
On January 26, 1997, a Cessna 172 C Skyhawk, registration F-BKBA, was conducting a planned flight between Brive and Guéret. While cruising at flight level 35 with the engine operating at 2500 RPM, the pilot observed a rapid decrease in engine RPM.
In an attempt to rectify the issue, the pilot activated the carburetor heat control; however, this action caused a further reduction in engine power. The pilot quickly returned the control to its original position but was unable to restore power through subsequent adjustments to the throttle or the fuel selector. Given the deteriorating engine performance, the pilot decided to perform an emergency landing in a field. During the final approach, the engine RPM had dropped to approximately 1200 RPM. The aircraft landed on a hillside without sustaining any damage to the airframe or the engine.
Approximately thirty minutes after the landing, the pilot attempted to reposition the aircraft, at which point the engine restarted without difficulty.
The investigation
The investigation focused on the sequence of engine malfunctions and the environmental conditions present during the flight. Meteorological data recorded at the site indicated anticyclonic conditions with visibility between 2 and 3 km, scattered stratus clouds at 800 feet, and a ground temperature of 6°C with a dew point of 4°C. The investigation examined the pilot's actions regarding the carburetor heat control and the subsequent engine behavior during the landing and restart.