Williams John TITAN T-51 MUSTANG accident near Geneva, Ohio, July 21, 2024

The NTSB's narrative final · quoted from the NTSB record

The pilot, who was the builder of the experimental amateur-built airplane, was conducting a post-maintenance test flight. After performing several aerobatic maneuvers near the airport, the pilot began a high-speed low pass over the runway. Upon passing most of the runway, the airplane began a climb. A witness heard the engine go to a high rpm and then saw the entire propeller hub break apart. After the propeller hub fractured and separated, the airplane began a left turn toward a road. While maneuvering toward the road, the airplane’s left wing impacted a tree and the airplane subsequently rolled over and impacted terrain. Onboard recorded data revealed that, at the time the propeller separated, the engine was operating at 6,813 rpm, which equated to a propeller speed of 3,585 rpm. This speed was considerably in excess of the propeller blade blank manufacturer’s limit of 2,100 rpm. This speed would have produced a centrifugal force that was more than 3 times the design limit of the propeller blade blanks. Further examination of the onboard data revealed that, around the time of the propeller overspeed, the airplane was traveling at an airspeed about 223 miles per hour (mph); the published never-exceed speed (Vne) for the airplane was 215 mph. The data also revealed a sudden decrease in the longitudinal load factor, consistent with a sudden deceleration of the airplane, followed shortly thereafter by the longitudinal load factor returning to normal. A possible reason for the deceleration was a sudden increase in drag from the propeller blades moving to low pitch. This was followed by a reduction in drag on the airplane, which was likely due to the propeller separating from the airplane. Postaccident examination of the propeller governor, governor adapter, and the propeller gearbox revealed no evidence of any preacident mechanical failures or malfunctions that would have precluded normal operation. Ultimately, the reason for the propeller overspeed could not be determined based on available information.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.

Photographs from the investigation 12 pictures from the NTSB's docket, as the NTSB released them

Photograph 1 – Airplane at accident sitePhotograph 2 – Engine at accident sitePhotograph 3 – Propeller gearbox at accident sitePhotograph 4 – Propeller governor on test benchPhotograph 5 – Propeller bladesPhotograph 6 – Propeller hubPhotograph 7 – Propeller pistonPhotograph 8 – Engine after recoveryPhotograph 9 – No. 3 intake valve missing one valve keyPhotograph 10 – No. 1 piston with valve strike impressionsPhotograph 11 – No. 1 cylinder head with valvesPhotograph 12 – Propeller gearbox after disassembly

The NTSB's photographs with the NTSB's captions, at screen size. Open a picture to see it full size or to report one that should not be shown.