FTW03LA171 · Boyle Black Eagle BE360

The 1,222-hour pilot reported that during the flight several aerobatic maneuvers were completed with "no apparent abnormalities." A "half loop down" was initiated at an approximate airspeed of 95 to 100 mph. At the base of the maneuver, at an approximate airspeed of 160 to 170 mph, the pilot heard a "loud high pitch noise accompanied by a rapid decrease in airspeed." The pilot reduced the power to idle, increased the mixture to rich and cycled the propeller pitch to high, then to low. The pilot observed the tachometer "falling through 3,800 rpm." The pilot stated that "repeated attempts to bring the rpm within range using the throttle and propeller controls failed as the aircraft appeared to be descending between 500 and 1,000 feet per minute at an airspeed of 95 mph." During the descent, the pilot observed "the tachometer continuing to show the engine turning at 3,200 rpm with the throttle at idle." Subsequently, the pilot initiated a forced landing to a wheat field. During the landing roll, the left main wheel hit a hole, and the airplane nosed over and came to rest inverted. Examination of the propeller governor by a FAA inspector revealed, "small amounts of metal flakes were blocking the pressure relief valve from opening and to stick in the closed position." The propeller governor was sent to the manufacturer for further examination. The propeller governor was noted to be free of anomalies during the bench test and examination at the manufacturers facility.

Verbatim NTSB analysis and probable cause from the NTSB dataset