What happened
On 28 February 2018, a Cessna 182-P, registered N609PC, was conducting an IFR cross-country flight from Touquet-Côte d'Opale to Lognes-Émerainville. The aircraft was occupied by a pilot and a passenger.
Upon reaching FL 70, the crew detected abnormal engine noise, vibrations, and the smell of smoke. The pilot responded by shutting down the engine and attempting a restart, which was unsuccessful. The passenger, who possessed greater flight experience, took control of the aircraft and initiated an emergency call. Realizing that the destination aerodrome was unreachable, the passenger diverted to a field near Yonval, performing an off-helid field forced landing at approximately 09:40. There were no fatalities or injuries, though the aircraft sustained damage.
The investigation
Investigators examined the Continental O-470-R engine and reviewed data from the onboard Engine Data Management (EDM) computer. The engine had undergone maintenance 15 days prior to the accident, which included the replacement of cylinder No 2 following a previous report of vibrations.
Post-landing inspections revealed a perforation in the crankcase aligned with cylinder No 1 and the separation of the right magneto. Detailed laboratory analysis of the engine components showed that the damage was concentrated around the cylinder No 1 connecting rod. The investigation also compared this event to a previous accident involving a similar engine type (a Cessna U206F, registered F-HNCM) to determine if a common failure mechanism existed.
Findings
- The engine failure was caused by the fatigue failure of the cylinder No 1 connecting rod.
- The failure resulted in the fragmentation of the rod, partial destruction of the piston, and a sudden perforation of the crankcase.
- Data from the EDM computer showed a sudden, massive drop in exhaust gas temperature for cylinder No 1, consistent with the loss of compression following the crankcase breach.
- While traces of fatigue cracking were identified on the inner side of the rod cap, the investigators noted an abnormally high material hardness in that area, though they could not confirm if this hardness caused the crack or was a result of the subsequent intense heating.
- Although the fatigue initiation process differed from a previously documented similar engine failure, the ultimate mechanical consequences were identical.