On June 11, 2019, about 1451 mountain standard time, a Mooney M20V airplane, N576CM, was substantially damaged when it was involved in an accident near Deer Valley Airport (DVT) Deer Valley, Arizona. The private pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. About 5 months after the accident, the pilot succumbed to his injuries. A statement from the pilot was not obtained during the investigation. Review of air traffic control communications revealed that, about 7 minutes after departing from Scottsdale Airport (SDL), Scottsdale, Arizona, the pilot reported a “rough running engine” and subsequently declared an emergency. The airplane was about 8 miles northwest of DVT at the time of the pilot’s radio call. Radar data showed that the pilot had climbed the airplane to an altitude of 9,100 ft mean sea level. The controller informed the pilot of possible diversion airports, stating that Pleasant Valley Airport (P48), Peoria, Arizona, was near the airplane’s position and that Glendale Municipal Airport (GEU), Glendale, Arizona, was 12 miles south of the airplane’s position. The pilot elected to divert to GEU, and radar data showed that the airplane turned to the south onto a heading that aligned with runway 19. A few minutes later, when the airplane was at an altitude of about 4,700 ft mean sea level, the pilot recognized that the airplane was not going to reach GEU, so he made a turn toward DVT, which was about 8 miles to the east. No other transmissions from the pilot were recorded. Radar data showed that the airplane continued on an easterly heading until the last recorded target; at that time, the airplane was about 2 miles west of DVT. A witness, who was located near the accident site, reported that the airplane appeared to bank left to avoid high-tension power lines before it impacted two light posts and then the ground. A postimpact fire ensued. The airplane came to rest on a street. The postimpact fire consumed most of the airframe. Flight control continuity was established from the cockpit controls to all primary flight control surfaces. Engine control continuity was established from the cockpit controls to their respective engine components. An unmeasured amount of fuel remained in the left-wing fuel tank. Fueling records showed that, on the morning of the accident flight, the airplane tanks were filled with 58 gallons of 100 low-lead fuel. Postaccident examination of the engine revealed extensive thermal damage throughout. The engine was then shipped to the manufacturer for further examination. While preparing the engine for the test runs, several components and accessories were replaced due to thermal damage. The engine was successfully run at various power settings, but it would not run at idle. The metering assembly was removed and tested, and internal components were replaced. Hard deposits of what appeared to be melted plastic on the throttle body internal walls was removed. Afterward, the engine was successfully run. Postaccident examination of the airframe and engine revealed no mechanical anomalies or malfunctions that would have precluded normal operation.