What happened
On March 26, 2001, a Piper PA28-161, registration I-CNPG, was conducting a training flight from Cuneo Levaldigi Airport toward Cannes. Approximately seven minutes after takeoff, while climbing through 3,500 feet, the aircraft experienced a power reduction accompanied by engine vibrations. The pilot notified Cuneo AFIS of the intention to return to the departure airport.
Roughly one minute later, the vibrations intensified, and oil began leaking from the front left side of the aircraft's cowling, followed by a total loss of engine power. Realizing the aircraft could not reach the airport, the pilot declared a MAYDAY and performed a forced landing in an unplowed field near Montanera, approximately five miles south-southeast of Cuneo. There were no injuries to the four occupants, and no damage was reported to third parties.
The investigation
The investigation focused on the Lycoming 0-320-D3G engine, which had accumulated 4,000.53 total hours since its last overhaul in 1994. Examination of the powerplant revealed two holes in the upper part of the engine base, resulting in oil leakage and significant internal component damage.
Investigators determined that the failure was caused by the detachment of connecting rod number 2. The inspection showed that the parts involved did not exhibit signs of overheating or seizing, and the torque measurements on undamaged components were within correct specifications. The parts used in the engine were identified as correct replacements according to their markings.
Findings
- The primary cause of the engine failure was the failure of a connecting rod bolt on rod number 2.
- The failure likely occurred when one bolt snapped, subsequently causing the second bolt to bend and break.
- Given the high total time of the engine, the failure was likely a progressive fatigue phenomenon, although the specific trigger for the initial fracture could not be determined.