Accident to the Robin DR400 - 120 registered F-GSBK on 03/09/2018 at Bénodet (Finistère)

Cat. 2 investigation report: simplified-format report, adapted to the circumstances of the occurrence and the investigation stakes.

During a local flight off the south coast of Brittany, one of the four engine cylinders failed while en route. This failure was the consequence of a fatigue cracking phenomenon in the steel barrel of the cylinder. The condition of the fracture seems to indicate that this process had started some time previously without, however, being able to date it. The only singularity found in line with this fracture was the presence of corrosion. The pilot managed to return to the coast with the residual engine power. The engine then shut down and the pilot landed on a beach. During the landing run, the aeroplane turned over onto its back and came to a stop in the water.
The absence of recorded leak rate measurements in the last two 100-hour maintenance inspections did not enable the possible detection, during inspections, of an anomaly on the cylinder which failed. In addition, the available maintenance data did not mention annual searches for corrosion on F-GSBK due to its operation in a salt-laden environment.
The safety investigation was not able to determine the contributing factors to the damage phenomenon which led to the complete failure of the cylinder in flight.