Jackson Velocity accident near Mack, Colorado, September 3, 2019

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

The commercial pilot departed on a business flight in the experimental airplane in visual meteorological conditions. As the airplane was passing 15,000 ft en route to its assigned cruising altitude of 18,000 ft, the propeller started to overspeed. The pilot reduced the propeller rpm and manifold pressure but reported that he was unable to find a power setting that would allow the airplane to maintain level flight. Air traffic control provided the pilot with vectors to a nearby airport, where the pilot performed a power-off approach and waited until the landing was assured before lowering the landing gear. The airplane touched down halfway down the runway. The main landing gear was not completely extended, rendering the brakes inoperable, and during the landing roll, the airplane impacted an irrigation pipe, slid off the departure end of the runway, and came rest in a field. Postaccident examination revealed no discrepancies with the propeller or governor. The screws securing the electronic ignition timing ring to the three brackets bolted to the crankshaft at the propeller stud flange had failed, damaging the timing disk and sensors. The damage caused by the loose screws caused the engine to slow from about 2,700 rpm to about 2,550 rpm. The propeller governor then decreased the propeller pitch to bring the propeller rotation back up to speed, but once the obstruction of the ingested screws cleared and the friction was released, the low-pitch blades allowed the propeller to overspeed. Thus, the overspeed was likely caused by the propeller governor's reaction to a slight slow down of engine speed when the timing ring attachment screws backed out and damaged the electronic ignition timing sensors.

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.