F4U-7 N965CV accident near Jerome, Idaho

Probable cause

The pilot’s decision to fly the airplane with a known mechanical deficiency.

NTSB analysis

Following an annual inspection, the mechanic who conducted the inspection was unable to conduct a test flight due to weather conditions but did perform several engine runs, during which he adjusted the fuel enrichment setting. The mechanic told the pilot before the accident flight that he would have to lean the engine manually while on the ground instead of using the auto-lean mixture setting, as the engine would run rich.

Before taking off, the pilot placed the mixture in the auto-lean position. The engine sputtered, and the pilot saw black smoke originate from the exhaust. The pilot then manually leaned the engine, and “it cleared up.” The pilot placed the mixture in the auto-rich position, performed a magneto check, then taxied onto the runway, but the engine “loaded up” a second time. The pilot stated that he manually leaned the engine, then moved the mixture to the auto-rich position while he advanced the throttle to 30 inches of manifold pressure. He said that he held this power setting for about 1 minute before initiating the takeoff. As the airplane accelerated past about 100 to 110 knots, the engine “coughed”, and the pilot reduced power to idle and aborted the takeoff but “ran out of runway.” The airplane exited the right side of the runway and impacted a dirt berm and fence before it came to rest upright.

Postaccident examination of the engine revealed no evidence of any mechanical malfunction that would have precluded normal operation and production of power, which included no evidence of preignition or detonation within each cylinder. During functional tests of the carburetor, it was found that, at high power settings, the fuel flow was lower than specified limits and would result in a lean fuel/air mixture. However, at lower power settings, the fuel/air mixture was within or slightly higher than specified limits. While it is likely that the lean fuel/air mixture at higher power settings could have resulted in detonation, no signatures were observed to suggest that it occurred.

The pilot stated that he wanted to get the airplane to an airshow and relied on the information provided to him by the mechanic. He reported that, in hindsight, he should have not flown the airplane and had the carburetor removed for overhaul.

Text from the NTSB. Open the NTSB docket for WPR19LA157 for the full record.