Engine Failure After Maintenance

Location: Phoenix, AZ Accident Number: WPR20LA144
Date & Time: 05/13/2020, 0842 MST Registration: N201HH
Aircraft: Mooney M20J Injuries: 2 None
Flight Conducted Under: Part 91: General Aviation - Personal

On May 13, 2020, about 0842 mountain standard time, a Mooney M20J airplane, N201HH, was substantially damaged when it was involved in an accident near Phoenix Deer Valley Airport (DVT), Deer Valley, Arizona. The commercial pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

According to the pilot, the purpose of the flight was to observe the airplane's performance following a propeller overhaul that was completed about 2 weeks prior. The pilot performed two initial ground runs prior to the accident, but was unable to achieve maximum takeoff rpm on either occasion. Following each ground run, the pilot would return the airplane to his hangar where an airframe and powerplant mechanic would make adjustments to the propeller governor.

On the day of the accident, the pilot departed with the mechanic onboard and observed 2,580 rpm on the tachometer as he climbed to 6,000 ft mean sea level. He then leveled off and retarded the throttle to 2,500 rpm. After observing a stable cruise power setting for several minutes, they decided to return to DVT. However, almost immediately the engine advanced to 2,850 rpm without any intervention from the pilot who promptly retarded the propeller lever until he observed 15 inches Hg on the manifold pressure gauge. At this time, the engine continued to function, but it sounded erratic and could not be manipulated by throttle movement.

They were about 2.5 nm from the airport and in a descent when they encountered catastrophic engine failure and lost all power. The pilot selected a landing area with minimal vegetation and deployed the landing gear. During touchdown, the airplane landed hard and slid before it came to rest in a shallow gulley.

The airplane and engine were recovered for examination.

FMI: www.ntsb.gov