Accident Overview
On May 13, 2020, at approximately 0842 mountain standard time, a Mooney M20J airplane, registration N201HH, was substantially damaged during a forced landing near Phoenix Deer Valley Airport (DVT), Deer Valley, Arizona. The pilot and passenger were not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight to test engine performance after propeller and propeller governor reinstallation.
Pre-Accident Events
The pilot, who also owned the airplane, had the propeller and propeller governor overhauled due to an oil leak from the propeller hub. The overhaul facility informed the pilot that both components needed to be synchronized. Following reinstallation on May 1, 2020, approximately 1.5 hours before the accident flight, the pilot and his mechanic performed ground run-ups and adjustments but could not achieve the rated 2,700 rpm; they observed a maximum of 2,600 rpm and proceeded to test takeoff performance.
The day before the accident, a takeoff attempt was aborted after the engine reached only about 2,350 rpm. Further adjustments to the governor were made, including removal of a second gasket during installation.
On the accident day, the pilot and mechanic conducted an engine run-up on runway 22 with no anomalies noted. During takeoff, the engine reached 2,600 rpm, and the pilot continued the climb to 6,000 feet mean sea level. At that altitude, cruise power was set to 2,500 rpm and 25 inches of manifold pressure. Shortly thereafter, the engine oversped to 2,850 rpm. The pilot reduced manifold pressure and declared an emergency. The engine became erratic, producing thrust but not responding to propeller lever adjustments. While descending toward runway 25R at 2,500 feet about 2.5 nautical miles from the airport, total engine power was lost. The pilot executed a forced landing to an area with minimal desert vegetation, but the airplane impacted rough terrain.
Post-Accident Findings
Postaccident photographs provided by the Federal Aviation Administration (FAA) showed substantial damage to the stabilator.
Initial inspection of the engine revealed two large holes in the crankcase, metallic debris throughout the oil pan, and an obstructed oil suction screen. Disassembly showed that the cylinder No. 3 and 4 connecting rod caps and bolts had separated from the crankshaft. Other connecting rods were unremarkable. According to the FAA handbook, connecting rod caps and bolts secure the rod to the crankpin.
Materials laboratory examination using a scanning electron microscope identified fatigue striations on a cylinder No. 4 cap remnant, with cracks associated with wear or spalling of the surface layer. Metallography revealed intergranular cracking initiating from the inner surface. The bolts fractured from overstress. Chemical analysis confirmed alloy steel composition and detected lead and bromine, consistent with combustion products of brominated tetraethyllead additives in aviation fuel. The crankshaft showed no fractures or large cracks, only smearing on cylinder 3 and 4 journals.
Engine data from an onboard monitoring instrument showed a rise in oil temperature starting at 0836:40, about two minutes before data ceased. Simultaneously, exhaust gas temperature (EGT) for cylinders No. 1 and 4 decreased suddenly. Oil temperature peaked at about 250°F at 0837:30, when EGT for the other cylinders also dropped.
Propeller examination found witness marks consistent with low rotational absorption at impact; no pre-impact mechanical failure was identified. The propeller governor was partially seized due to debris; analysis found foreign material consistent with internal engine components. The gasket on the governor was not a McCauley part and lacked a filter at the oil inlet to capture debris.
The engine manufacturer reviewed photographs of the failed connecting rod caps and bolts and noted evidence of thermal damage and high heat at the crankshaft, consistent with absence of lubrication and excessive heat.
Probable Cause
No probable cause was stated in the source.