NTSB Factual Report

On January 2, 2016, about 1430 Pacific standard time, a Kevin Metzler Velocity STD RG experimental amateur-built airplane, N133SV, was substantially damaged following a loss of engine power and subsequent forced landing about 1 mile northwest of the Rosamond Skypark Airport (L00), Rosamond, California. The private pilot, who was the owner and sole occupant of the airplane, was not injured. Visual meteorological conditions prevailed for the local flight, which was being operated in accordance with 14 Code of Federal Regulations Part 91, and a flight plan was not filed. The local flight departed L00 about 5 minutes prior to the accident.

In a report submitted to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), the pilot reported after taking off he climbed with the engine rpm set at about 4,500, "…which was well below the engines rated redline of 5,400 rpm." The pilot stated that when he reached an altitude of 7,000 ft, he noticed that the [engine] temperature was much higher than it had been the previous day, which prompted him to level off and reduce power. Shortly after the power reduction the engine began to surge; at this time the pilot decided to return to the departure airport, about 10 miles to the east of his location. The pilot reported that he attempted to maintain as much altitude as possible, and while en route the engine began to lose power, which made altitude more difficult to maintain. The pilot opined that when he realized that he would not be able to make it to the airport, he elected to land in a vacant field about one and one-half miles west of L00. After landing with the gear retracted, the airplane came to rest in an upright position.

The airplane, which was equipped with a Subaru EG-33 engine, serial number 007708, rated at 230 horsepower, had accumulated a total of 6.8 hours since its most recent overhaul; the total engine time was unknown. The pilot reported that the most recent condition inspection was performed on December 1, 2015, at a total airframe time of 66.8 hours.

An initial postaccident examination of the engine revealed that the No. 1 connecting rod assembly had failed, which resulted in the loss of power. The NTSB IIC took possession of the connecting rod assembly, in addition to two pieces that had separated from the assembly. The retained parts were shipped to the NTSB Materials Laboratory in Washington, D.C., for examination and analysis by a Senior Metallurgist. As a result of his examination, the metallurgist reported that the connecting rod assembly had fractured in four areas. An attachment bolt and nut remained attached to a fractured piece of the arm and cap portion. The second attachment bolt, a portion of the second arm, and a portion of the cap had separated from the connecting rod assembly, however, were not recovered during the investigation. Additionally, examination of the fracture faces revealed fatigue cracks emanated from multiple origins at the machined cut out area adjacent to the through-hole for each attachment bolt. Fatigue cracks with multiple origins where also observed on the mating fracture faces. The fatigue crack origin areas were aligned and parallel to circumferential machine marks. The rough texture of the fatigue crack features was consistent with a fatigue crack that had propagated under high stress. The fatigue crack in each mating fracture propagated through at least 50% of the wall. Further, the fracture faces outside of the fatigue regions exhibited rough dimple texture features consistent with overstress separation. The round surfaces that corresponded to the location of the bearings showed evidence of rough circumferential gouge marks, but no evidence of heat tinting was observed. (Refer to the NTSB Materials Laboratory factual report, which is appended to the docket for this accident.)

On January 26, 2016, under the supervision of the NTSB IIC, an examination of the engine was performed at the facilities of Outfront Motorsport, located in Santa Ana, California. With the exception of the engine's No. 1 connecting rod assembly which had failed, and the stuck piston of the pressure relief valve on the oil pump, there were no anomalies observed with the engine that would have precluded normal operation. According to the Outfront Motorsport general manager, during normal operations the pressure relief valve opens to relieve oil pressure when it is too high, and remains closed in order to build and sustain oil pressure. When observed during the postaccident examination, the piston portion of the valve was stuck closed. When the component was liquid tested to check for leakage past the piston, the valve retained liquid, which indicated that the valve was not stuck in the open position. After the piston was forced to the open position, debris was observed in the component which had kept it closed. The debris was consistent with bearing material that had invaded the area subsequent to the engine failure.

NTSB Probable Cause

A partial loss of engine power due to failure of the No. 1 connecting rod as a result of multiple fatigue cracks for reasons that could not be determined during on postaccident examination.