What happened
On April 9, 2017, a Cessna 206F, registration F-HNCM, was performing aerial work involving parachute jumps near Sainte-Marie-au-Bosc, France. The pilot had departed from Le Havre airfield for the tenth flight of the day, carrying four passengers.
While climbing through approximately 4,000 feet over the sea, the engine suddenly ceased operation. The pilot immediately transitioned the aircraft toward land, adjusting the pitch trim to maintain the best glide speed. During the attempt to restart the engine, the powerplant ran for roughly ten seconds while exhibiting intense vibrations, smoke, and oil spray, before failing completely.
Seeking a suitable landing site, the pilot identified a clear field for an emergency descent. During the landing roll, the nose gear sank into the soft ground, causing the aircraft to overturn and land on its back. There were no fatalities among the five occupants, though the aircraft sustained heavy damage.
The investigation
The BEA examined the engine, a Continental IO-520-F, which had accumulated 2,809 total hours, including 1,166 hours since its last overhaul in 2003. The investigation also reviewed the pilot's recent flight history and the aircraft's maintenance records.
Technical analysis of the engine components revealed that the failure was caused by the breakage of several internal parts, specifically the connecting rods for cylinders 3, 4, and 5. Investigators identified evidence of fatigue cracking on fragments of the connecting rod from cylinder 4. This fatigue-related failure led to the rod separating from the crankshaft, which subsequently caused the subsequent, more violent failures of the other rods.
Findings
- The engine failure was triggered by the fatigue failure of the cylinder 4 connecting rod.
- The failure of the remaining connecting rods was a secondary effect of the initial breakage of the cylinder 4 component.
- While the material of the rod met manufacturer specifications, the precise origin of the fatigue crack could not be determined due to the extensive damage to the internal engine components.