ERA21LA222

The pilot reported that, while en route to the destination airport, the airplane lost total engine power. The pilot declared an emergency with air traffic control and began to divert to the nearest airport. The pilot recognized that the airplane would not be able to glide to the airport, and he decided to land on a road with the landing gear and flaps retracted. The pilot and passenger sustained serious injuries, and the airplane was substantially damaged. A postaccident teardown examination of the engine revealed that the No. 4 connecting rod was fractured midspan. One of the No. 4 connecting rod bolt nuts was found in the oil pan and exhibited no signs of pre- or postaccident damage. The cotter pin for that nut was not found; the other No. 4 connecting rod nut was found secured to its bolt with the cotter pin installed. Additionally, all other connecting rod bolt nuts remained attached to their respective bolts with cotter pins in place. Thus, it is likely that the nut found in the oil pan was not secured with a cotter pin and that the unsecured No. 4 connecting rod bolt nut became loose over time and backed out of the connecting rod bolt during the accident flight, resulting in the total loss of engine power. Review of maintenance records revealed that the engine had accumulated about 1,240 hours of operation since major overhaul, which was completed more than 28 years before the accident. The engine manufacturer recommended that the engine be overhauled every 2,000 hours or 12 calendar years, whichever occurred first. The investigation could not determine when the No. 4 connecting rod nut was installed without a cotter pin.

On May 20, 2021, about 0930 eastern daylight time, a Mooney M20K, N9514R, was substantially damaged when it was involved in an accident near Dawson Municipal Airport (16J), Dawson, Georgia. The pilot and passenger sustained serious injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, he had recently purchased the airplane. On the day of the accident, the pilot conducted a preflight inspection with no anomalies noted, and the airplane departed Orlando Apopka Airport (X04), Apopka, Florida, about 0815 for a flight to Birmingham-Shuttlesworth International Airport (BHM), Birmingham, Alabama. While en route to the destination airport, the airplane lost total engine power. The pilot declared an emergency to air traffic control and diverted to the nearest airport, which was 16J. During the descent, the pilot operated the engine controls with no response from the engine. The pilot realized that the airplane would not reach the airport, and he landed the airplane on a road with the landing gear and flaps retracted. The airplane’s right wing and fuselage were substantially damaged. A postaccident teardown examination revealed two holes in the top of the engine crankcase, with the larger hole near the center and the smaller hole just aft. The cylinders remained attached to the crankcase. The No. 4 connecting rod was found fractured about midspan. A No. 4 connecting rod bolt nut was found in the oil pan. This nut exhibited no signs of impact damage or damage that would be consistent with separation. A cotter pin associated with the nut was not located. The other No. 4 connecting rod nut was found secured to its bolt with the cotter pin installed. All other connecting rod bolt nuts remained attached to their respective bolts with cotter pins in place. The oil filter pleats and oil sump contained a large amount of metallic debris. Review of maintenance records revealed that the engine had accumulated about 1,240 hours of operation since its last major overhaul, which was completed on September 18, 1992. The engine manufacturer recommended that the engine be overhauled every 2,000 hours or 12 calendar years, whichever occurred first. Further review of the records revealed that the engine was disassembled, cleaned, and inspected due to a crankcase crack in 2005 and that the No. 3 cylinder was replaced in 2013.