What happened
On July 15, 2017, a Costruzioni Aeronautiche Tecnam P92 airplane, registration N561TU, was on a return flight to Bay Bridge Airport (W29) in Stevensville, Maryland. The flight was being conducted under VFR conditions with 10 miles of visibility and light winds.
While entering the traffic pattern for runway 29, the pilot reduced engine power to configure the aircraft for landing. Shortly after the power reduction, the engine began running rough. The right-seat pilot took control of the aircraft. As the pilots attempted to manage their glidepath to avoid a nearby residential area, the engine abruptly stopped.
Realizing the aircraft would not reach the runway, the pilot directed the airplane toward a cleared area of open ground. The aircraft struck an earthen berm and continued into a second berm, causing the nose and right main landing gear to separate from the airframe. The two pilots were not injured.
The investigation
Investigators examined the Rotax 912 ULS engine, which had only 13.2 hours of total operating time. While engine data from the Garmin G3X showed steady fuel pressure, oil temperature, and cylinder head temperature until the failure, physical examination revealed that the No. 1 cylinder was heavily damaged. The exhaust valve was found deformed in an "S" shape inside the combustion chamber, and a hole was present in the piston.
Technical analysis of the engine components revealed that the exhaust valve spring retainer had fractured due to fatigue. Metallurgical examination via electron microscope showed pronounced vibration stripes on the fracture surface. Additionally, investigators found that the oil pump drive pin showed excessive wear and the magnetic plug was covered in metallic particles.
Further investigation into the lubrication system identified that air could be introduced into the system through several methods, such as exceeding a 40-degree bank angle, insufficient purging of the system after maintenance, or spinning the propeller in reverse. Testing confirmed that trapped air in the hydraulic valve tappets could take several minutes to vent, potentially overloading the valve train and leading to the fatigue failure observed.