Amateur-built 601XLB accident near Jamul, California, August 15, 2019

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

The pilot was operating an experimental amateur-built airplane on a personal flight. During cruise flight, the engine lost all power, and the pilot performed a forced landing into a field. During the landing roll, the airplane struck a large rock and sustained substantial damage to the left wing and forward fuselage. The airplane’s engine control unit (ECU)—part of the airplane’s full-authority digital engine control system—managed the engine’s electrically powered ignition system. Review of data from the ECU and the airplane’s electronic flight information system revealed that the engine stopped operating because the ECU shut down suddenly. The battery that operated the full-authority digital engine control system appeared to be providing enough electrical power to the system bus for the ECU to operate; thus, the source for the loss of electrical power could not be determined. Subsequent examination of the airplane revealed no anomalies with the ECU or airframe wiring, although an undiscovered intermittent electrical supply failure to the ECU could not be ruled out. The airplane was not equipped with a redundant electrical power source or a backup ECU system. As a result, when the engine control unit shut down suddenly, no system could provide the ECU with the electrical power that would have allowed it to continue operating.

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.