Incident Overview
On 17 September 2020, a Tecnam P2006T (registration SP-ADF) departed from EPWT for a training flight with an instructor and a student pilot. Approximately 18 minutes into the flight, at an altitude of 3,200 feet, the right engine experienced a drop in RPM and ceased operation about 30 seconds later. The crew returned to the departure airport and landed safely on the remaining engine without further incident.
Investigation Findings
Post-flight inspection of the right engine revealed a partially unscrewed bolt securing the valve cover on cylinder #1. Magnetic plug inspection showed metallic chips, and trace amounts were found in the oil filter and oil. The engine had leaked oil, with only 1 liter remaining after the flight. The coolant level was normal.
The engine was removed and sent to Faston for detailed examination. Disassembly identified scoring of the connecting rod bearing on cylinder #1 on the crankshaft, resulting in damage to the connecting rod, cylinder, and piston. Fragments of the cylinder and piston were found in the oil pan and reduction gearbox.
The investigation determined that the engine seizure was caused by an oil leak resulting from the loosening of the valve cover bolt. The reason the bolt loosened was not established. According to the engine maintenance manual, the valve cover bolt is tightened during engine installation, and no periodic checking is required during routine operation. Visual inspections during scheduled maintenance should detect loose bolts or oil leaks, but experience indicates that the rubber gasket can hold the cover in place even when the bolt is loose, making detection difficult.
Probable Cause
The spontaneous loosening of the valve cover bolt on cylinder #1 of the right engine, leading to an oil leak and subsequent engine seizure.
Aircraft and Engine Details
The aircraft, a Tecnam P2006T, was equipped with a Rotax 912 UL engine installed on the right side. The engine had been mounted on the airframe by a previous owner in Italy in 2016. The current owner had been operating the aircraft since March 2020.
Safety Recommendations
The investigation accepted preventive measures proposed by the operator, including checking the torque of valve cover bolts on all Rotax engines, applying torque seal marks to each bolt, and adding a 50-hour maintenance task to retorque the valve cover bolts. No additional safety recommendations were issued by the commission.