Accident Overview
On July 15, 2017, at about 1615 eastern daylight time, a Costruzioni Aeronautiche Tecnam P92 airplane, registration N561TU, was substantially damaged during an accident near Stevensville, Maryland. The two private pilots aboard were not injured. The flight was conducted as a personal flight under Title 14 Code of Federal Regulations Part 91.
Flight Details
The aircraft had been recently purchased and placed on a lease-back operation with the operator. Two days before the accident, the owner and the right-seat pilot took delivery of the airplane in Apopka, Florida, and flew it to Bay Bridge Airport (W29) in Stevensville, Maryland. On the day of the accident, the airplane was fueled with about 16 gallons of fuel (8 gallons per side) for a planned roundtrip flight to Shoestring Aviation Airfield (OP2) in Stewartstown, Pennsylvania. Prior to the return flight, the left-seat pilot checked the oil, coolant, and fuel; all levels were normal, and there were about 12 gallons of fuel remaining.
Engine Failure and Forced Landing
Upon returning to the W29 area, the pilots obtained current weather conditions and entered the traffic pattern for runway 29. They observed no other traffic and conducted the downwind leg about 2 miles south of the airport due to noise-abatement rules. The left-seat pilot reduced engine power and began configuring for landing abeam the runway numbers. Shortly after, the engine began running rough. The right-seat pilot took control; both pilots scanned engine indications but saw no anomalies. The right-seat pilot turned onto the base leg but did not turn directly toward the runway to avoid arriving too high and overflying a townhouse community. The pilots increased flaps to correct for a high glidepath. About 20 seconds later, the engine stopped completely.
The right-seat pilot turned toward the runway threshold, but both pilots determined the airplane could not reach it. They selected a cleared but rough area about 45 degrees left of their flight path. The airplane struck an earthen berm and settled onto rough ground. During the landing roll, about 150 feet from touchdown, it struck a second berm. The right main and nose landing gears separated, and the airplane came to rest 20 to 30 feet beyond the second berm. The pilots shut off both fuel valves and the master switch before egressing.
Post-Accident Examination
The airplane was equipped with a Garmin G3X electronic flight instrument system; data download showed that fuel pressure, cylinder head temperature, and oil temperature remained steady until power loss. The airframe sustained substantial damage: nose gear separated, right main gear bent, left main gear damaged, one propeller blade broken, engine pushed back, engine mounts bent, firewall buckled, and multiple areas of crush damage on the fuselage and wings. External engine examination found the air filter clean and exhaust system damaged but no anomalies. The cooling system was intact; the oil line between the oil cooler and thermostat was kinked from impact, and the Nos. 2/4 carburetor was displaced. The propeller gearbox rotated smoothly. Spark plugs appeared normal with gaps of 0.19 inches. Carburetor float bowls contained automotive gasoline, with no anomalies noted. Both mechanical and electric fuel pumps were functional.
No oil was found in the line between the oil thermostat and oil pump. The oil pump drive pin showed excessive wear relative to engine operating hours. The magnetic plug was covered in metallic particles; the oil filter was clean. Cylinder No. 1 exhibited substantial damage and bluing; the exhaust valve spring retainer was fractured, and the cotter was partially fractured. Galling was visible on the exhaust valve bore. The hydraulic lifter for the exhaust valve had a small indentation and was easier to depress than the intake lifter. The pushrod had a ridge; the rocker arm showed impact damage. The exhaust valve was found in the combustion chamber, chipped, bent, and deformed into an S shape. A hole was visible in the piston. No anomalies were found in cylinders 2, 3, and 4. The crankshaft was twisted and would not rotate; the camshaft showed no visible anomalies.
Additional Findings
In November 2018, the No. 1 cylinder head, cylinder, oil pump assembly, oil tank, and oil cooler were examined at Rotax Aircraft Engines in Austria. Electron microscope examination of the valve spring retainer fracture surface revealed fatigue with pronounced vibration stripes. The heat treatment and statistical process control values met specifications. Examination of the cylinder head showed unusual wear on shim spring contact surfaces, indicating increased spring movement. Hardness tests met specifications. Hydraulic valve tappets showed noticeable wear on oil control plates. The oil pump, oil tank, and oil cooler showed no abnormalities. A small oil sample from the hydraulic tappets was analyzed; lead content indicated leaded fuel use, nickel was elevated, silicon was increased (possibly dust or silicone materials), and molybdenum and barium were unusual.
Between 2019 and 2020, four additional valve spring retainer fractures occurred in the United States involving aircraft N1PJ, N204BF, N117BF, and N562TU. Examinations of those engines revealed similar failures: intake or exhaust valve failures with broken valve spring retainers, and fatigue with vibration stripes on fractured surfaces. All parts met specifications.
Review of Rotax service documents indicated that air could enter the oil system through exceeding the 40-degree bank angle limit, poorly vented hydraulic tappets, lack of proper oil purging, spinning the propeller in reverse, or opening the oil system during maintenance. A test run of a Rotax 914 engine showed that intentionally trapped air took about 6.5 minutes at 2,538 rpm to vent from the hydraulic tappets.