Pilot Debrief

ROBERT L THURMOND RV8 near Centerville, UT — 2023-10-10

Final reportWPR24FA010
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Date
2023-10-10
Location
Centerville, UT, USA
Airport
BTF
Aircraft
ROBERT L THURMOND RV8
Registration
N75RT
Category
Airplane
Highest injury
Fatal
Fatalities
1
Phase of flight
Initial climb

Probable cause

The pilot’s exceedance of the airplane’s critical angle of attack while attempting to return to the departure airport, which resulted in an aerodynamic stall at an altitude too low for recovery. Contributing to the accident was the failure of the No. 2 connecting rod due to oil starvation for reasons that could not be determined.

Contributing factors

Contributing to the accident was the failure of the No. 2 connecting rod due to oil starvation for reasons that could not be determined.

NTSB narrative

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.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Pilot could have aborted the flight after noticing low oil pressure.

NTSB coding

Evidence available

  • FDR / data
  • Photos
  • 17 docket documents
View NTSB final reportView NTSB docket

Docket documents17

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