What happened
On the night of April 8, 2019, a Robin DR400-180, registration F-GEKG, was performing a training flight at Nîmes Garons airport. The flight, operated by Ecole Airways College, involved a student pilot and an instructor returning from a dual flight to Montpellier Méditerranée. After completing a touch-and-go on runway 18, the aircraft entered its second runway circuit.
During the downwind leg of this circuit, the instructor activated the carburetor heat control. As the aircraft turned onto the base leg, the engine speed decreased. Although the instructor applied power to restore the engine to 1,600 rpm, the engine speed dropped abnormally once the power was reduced to level off the aircraft. The engine subsequently stopped, forcing the instructor to take control. Unable to reach the runway, the instructor performed a forced landing into the runway approach lights, resulting in severe damage to the aircraft.
The investigation
The investigation focused on the engine's performance and the environmental conditions at the time of the accident. Investigators examined the fuel system and found sufficient fuel in the tanks, and the engine was able to restart normally several days after the event. The aircraft was equipped with a Lycoming O-360 A3A engine featuring a carburetor heat system, though it lacked a carburetor temperature indicator.
Meteorological analysis revealed that the area was experiencing a temperature inversion with high humidity. At the time of the accident, the air temperature near the ground was approximately 11°C with a dew point of 7°C, and significant dew was noted on the aircraft and ground. Radar data also indicated that the flight had been conducted at lower altitudes than the VFR minimums for that route, specifically flying at 900 ft and 1,300 ft over certain areas.
Findings
- The primary cause of the engine shutdown was carburetor icing.
- The flight conditions, characterized by high humidity and a temperature inversion, were highly conducive to severe icing.
- The pilots did not use the carburetor heat preventatively during the transition from the crosswind leg to the downwind leg.
- The decision to fly at a low altitude and an economical cruise speed increased the risk of icing, as the pilots did not anticipate the icing potential associated with the moisture levels and flight over bodies of water.