What happened
On Saturday, January 22, 2000, a Robin DR 315, registration F-BTJB, was conducting a cross-country flight between Moret and Etampes. While cruising at approximately 1,500 feet, the pilot observed a rapid drop in engine speed, which decreased from 2,200 to 1,500 RPM. Although the engine speed stabilized briefly, it continued to decline steadily.
The pilot attempted to activate the carburetor heat to mitigate the issue, but the action had no effect on the engine performance. As the engine power continued to diminish, the pilot attempted to divert the aircraft toward the Buno-Bonnevaux aerodrome. However, the engine eventually stopped, forcing the pilot to perform an emergency landing in an open field near Milly-la-Forêt.
The investigation
The investigation examined the meteorological conditions and the mechanical state of the aircraft. At the time of the incident, weather observations from Melun indicated a temperature of 4°C with a dew point of 3°C, accompanied by a cloud base at 2,000 feet. These conditions were identified as highly conducive to icing. Upon inspection on the ground, the engine was found to be functional and restarted immediately upon the first attempt.
Findings
- The primary cause of the engine failure was carburetor icing occurring during cruise flight.
- The atmospheric conditions, characterized by high humidity and temperatures near freezing, provided the necessary environment for ice to accumulate in the carburetor.
- The pilot was flying at the edge of the cloud layer, which contributed to the encounter with icing-prone air.