What happened
On 3 September 2018, a Robin DR40-120, registration F-GSBK, was conducting a local flight from Quimper Pluguffan aerodrome toward the Glénan islands. The pilot, accompanied by two passengers, had descended to approximately 500 feet to allow for sightseeing. During the flight, the pilot attempted to climb, but the engine failed to respond to power adjustments. The engine began to vibrate heavily, accompanied by smoke from the cowling and oil spraying onto the canopy.
Unable to find a suitable landing site on the islands, the pilot utilized the remaining engine power to return to the mainland. While attempting an emergency landing on a beach, the pilot had to adjust the approach path to avoid a person on the shoreline. During the landing run, the aircraft veered toward the water's edge, turned over onto its back, and came to a rest in the sea. The two passengers and the pilot evacuated the aircraft without assistance, though one passenger sustained injuries and the aircraft suffered substantial damage.
The investigation
Investigators examined the Lycoming O-235-L2A engine and found that the fourth cylinder had suffered a complete failure of its steel barrel near the base plate. The examination revealed that the rod and piston assembly of this cylinder had separated from the engine. While the engine showed no signs of unusual lubrication, investigators noted superficial corrosion on the surfaces of the cylinders and an absence of protective paint in the area of the fracture.
Maintenance records were also reviewed. While a 50-hour inspection had been performed in August 2018, the records for the two most recent 100-hour inspections (July and August 2018) did not include cylinder leak rate measurements. Furthermore, there was no evidence that the required annual corrosion inspections, mandated for aircraft operating in salt-laden environments, had been performed on this specific aircraft.