What happened
On 19 February 2011, a Reims Aviation Cessna 172M, registration EI-GSE, was conducting a general aviation navigation exercise from Weston Airport. The flight, which included an instructor and a student, was traveling northwest toward Donegal with planned diversions to test the student's skills.
While flying near Athboy, Co. Meath, the instructor observed the engine oil pressure drop significantly, approaching zero. Although the oil temperature remained stable, the instructor elected to terminate the training mission and return to Weston. However, as the aircraft approached Maynooth, the engine began running roughly and experienced a loss of RPM. Rather than attempting to reach the original destination, the instructor opted for an immediate forced landing at the nearby Dolly’s Grove private airfield. The landing on the asphalt runway was completed safely, and the two crew members exited the aircraft without injury.
The investigation
The AAIU examined the aircraft and the engine following the incident. While the aircraft appeared well-maintained and the external engine area showed no signs of leaks, a detailed teardown of the engine was conducted by an engineering firm in the UK. This inspection focused on the cause of the sudden drop in oil pressure.
Findings
- The investigation established that the engine suffered a catastrophic failure of the No. 3 connecting rod bearing insert.
- This failure resulted in the destruction of the bearing insert and caused mechanical damage and severe overheating to both the crankshaft bearing journal and the connecting rod big end housing.
- Debris from the failed bearing was found embedded in the piston skirts, and the crankshaft sustained minor impact damage.
- The instructor's decision to execute an immediate landing was timely and prevented further incident.
- The specific initiating cause of the bearing failure could not be determined from the technical inspection.