History of Flight
On September 28, 2020, at about 1800 eastern daylight time, a Tecnam P92 airplane, registration N562TU, was substantially damaged during a forced landing near Centerville, Maryland. The airplane was operated by Chesapeake Sport Pilot as a 14 CFR Part 91 instructional flight. The flight instructor and student pilot were not injured.
According to the flight instructor, the airplane was returning to Bay Bridge Airport (W29) in Stevensville, Maryland, when it suddenly began to vibrate severely. Engine rpm dropped from about 5,100 to 4,500. Onboard recorded data showed that fuel pressure, cylinder head temperature, and oil temperature remained steady until the power loss. The flight instructor took over controls and attempted different throttle settings, but the engine did not respond. He confirmed the fuel valves were on and turned on the electric fuel pump, with no change. Anticipating an engine failure, he configured for best glide, turned toward a field, and broadcast a mayday. About one minute later, the engine lost total power. He attempted to restart, but the engine would not crank and all avionics shut down. Approximately 30 seconds later, the displays came back on. The flight instructor landed the airplane in a soybean field. As the airplane slowed, the nose dropped, the nose landing gear dug into the soft earth and separated, and the airplane nosed over.
Aircraft and Engine Information
The Tecnam P92 is a strut-braced, high-wing, two-seat airplane made of sheet and tubular aluminum. It complied with FAA light sport aircraft rules. The airplane was manufactured in 2017 and had about 1,081 hours of operation at its most recent condition inspection on March 3, 2020. The engine, a Rotax 912 ULS2, was a 4-cylinder, horizontally opposed, 100-horsepower engine with a reduction gearbox driving a two-bladed, fixed-pitch Sensenich propeller. The engine had accrued about 734 hours of operation at the time of the inspection.
Wreckage and Engine Examination
Postaccident examination revealed substantial damage to the fuselage and both wings. The engine showed no anomalies in the oil system, with oil throughout. Aluminum debris and engine oil were found in the carburetors for cylinders Nos. 1 and 3. The No. 1 cylinder's exhaust valve spring retainer was broken, and the exhaust valve had fallen into the combustion chamber. The stem of the exhaust valve remained in place, but the head was detached. The No. 1 cylinder head, piston, and valves were damaged. The exhaust valve head was embedded in the intake valve, the piston had a large hole in its crown, the cylinder displayed damage, and the connecting rod was bent and twisted. The No. 3 cylinder head was removed, revealing metallic material in its combustion chamber, and the piston and cylinder showed damage.
Related Incidents and Corrective Actions
The NTSB had previously investigated a similar valve spring retainer failure in 2017 involving another Tecnam P92 (N561TU) operated by Chesapeake Sport Pilot. That engine, a Rotax 912 ULS2-01, had a fractured exhaust valve spring retainer. The root cause could not be determined. Between 2019 and 2020, four additional valve spring retainer fractures occurred in the United States (aircraft N1PJ, N204BF, N117BF, and N562TU). Examined engines showed broken valve spring retainers on cylinders Nos. 1 or 2. The Austrian Federal Safety Investigations Authority conducted metallurgical examinations at the engine manufacturer's factory. All parts met specifications, and fractured surfaces showed fatigue with vibration stripes.
In response to these occurrences, BRP Rotax revised service bulletins and instructions to include specific oil purging procedures, developed new valve spring retainers with improved materials, and urged distributors to communicate the information. Rotech Flight Safety distributed the revised documents and a clarifying video. Icon Aircraft issued a service letter advising that air entering the lubrication system could cause valvetrain failure and that certain flight maneuvers should be avoided.