WPR24FA010 · Robert L Thurmond RV8

During the pilot’s second flight in the experimental amateur-built airplane, he departed on a local, day visual flight rules (VFR) personal flight. A pilot-rated witness reported that, shortly after taking off, the pilot transmitted over the departure airport’s common traffic advisory frequency (CTAF) that the engine had a loss of engine oil pressure and, later, an engine failure. Recorded flight data showed the airplane depart and turn north. Shortly after departure, engine parameters showed a gradual decrease in oil pressure and, by 5 minutes after departure, the oil pressure had decreased to 13 psi. At this point in the flight, the pilot initiated a 180° left turn to the south and began a gradual descent until he briefly leveled off about 1,000 ft above ground level (agl). When the pilot turned back toward the airport, engine manifold pressure and rpm began to decrease and the recorded power output dropped to 49 percent. The airplane continued to descend and the pitch angle gradually increased. About 9 minutes after departure, the No. 2 cylinder exhaust gas temperature (EGT) decreased below the others, indicative of its failure, and the engine speed decreased to 2,300 rpm. The airplane entered a descending 16° right bank before abruptly rolling left to 32°, continuing until the last recorded data point near the site of the wreckage. The witness reported that the airplane appeared to have entered an aerodynamic stall about 100 to 200 ft agl; it then rolled left, descended, and impacted terrain in a left-wing-low, nose-down pitch attitude. Postaccident examination revealed a film of oil on the belly of the airplane that extended from the engine compartment to the tailwheel. The No. 2 cylinder connecting rod had separated from the crankshaft and breached the bottom of the crankcase. The mating surface of the crankshaft journal and the failed connecting rod showed damage consistent with the engine’s operation with insufficient oil. Oil residue was observed in the area around the propeller governor and propeller governor adapter. The propeller governor adapter exhibited multiple hairline fractures however, metallurgical examination of the fracture surfaces revealed they were consistent with overstress. The oil level gage tube was found separated from the crankcase. The oil dipstick was separated from the oil level tube gage. No oil residue was observed in the area surrounding the oil level tube gage. and was undamaged. The reason for the in-flight loss of oil could not be determined. The pilot had an opportunity to conduct an emergency landing at an Air Force base, about 5 nm north of where he made the 180° turn, as well as a dry lakebed about 4 nm to the southwest. Although the pilot was aware of an engine issue, and likely of its impending failure, he did not conduct an emergency landing. During the return to the departure airport, the pilot exceeded the airplane’s critical angle of attack, which resulted in an aerodynamic stall at an altitude too low for recovery.

Verbatim NTSB analysis and probable cause from the NTSB dataset