What happened
On July 25, 2013, a Robin DR40 and-120, registration F-GLKV, departed from Fontenay-Trésigny aerodrome for a flight to Lognes-Emerainville. The flight was an instructional session involving an instructor and a student pilot. After performing a touch-and-go maneuver, the aircraft began its initial climb. At an altitude of approximately 200 to 300 feet, the instructor noticed a significant loss of engine power, making it impossible to maintain level flight.
After verifying all engine controls and fuel settings, the instructor took command and turned right to seek a clear landing area. The aircraft performed a low-speed forced landing in a clearing near a lake. During the landing roll, the aircraft struck a reinforced concrete wall that was hidden by vegetation. The impact caused the wings to detach, and the fuselage subsequently slid down into the lake. Both the student and instructor were injured, and the aircraft was destroyed.
The investigation
The investigation focused on the engine's performance and the mechanical condition of the Lycoming O-235 L2A engine. Investigators found that the fuel tanks contained fuel and the fuel valve was open. While the propeller blades showed minimal damage—suggesting the engine was producing very little power—several internal mechanical issues were identified.
Testing of the magnetos revealed that one was non-functional and the other was performing poorly between 700 and 1,500 RPM. Additionally, the rocker arm clearance on cylinder number 3 was found to be out of tolerance, which could prevent proper valve closure. Significant wear was also noted on the intake rocker arm and the contacting cam. Because these issues were internal to the engine, they were not detectable during the most recent 50-hour or 500-hour maintenance inspections.