CEN21LA073

The pilot reported that he heard a loud “bang” and the engine began to vibrate and ultimately lost complete power. He executed a forced landing to a highway during which the airplane struck a car and a highway divider which resulted in substantial damage to both wings. Postaccident engine examination revealed that the Nos. 5 and 6 connecting rods had failed. Further examination revealed two undamaged rod nuts within the oil pan that had no remnant of a rod bolt within the threaded portion of the nut. Additionally, a rod bolt, although damaged, was complete from bolt head to threaded shank and did not have a nut on the threaded portion. Review of maintenance records revealed that the Nos. 1, 4, and 6 cylinders had been removed and replaced due to low compression about 8 years and 396 hours before the accident, but it is not known if the connecting rods were removed at this same time. The most recent engine overhaul was completed 16 years before the accident, and it had accumulated about 1,296 hours time-in-service since the overhaul. Based on the available evidence, the loss of engine power was likely due to improper connecting rod installation that resulted in the loss of connecting rod bolt torque, separation of the rod bolt nuts, and subsequent failure of the Nos. 5 and 6 connecting rods.

On December 2, 2020, about 2115 central standard time, a Bellanca 17-30A, N28067, was substantially damaged when it was involved in an accident near Arden Hills, Minnesota. The pilot and passenger and an occupant of the motor vehicle were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated the accident flight was a night sightseeing flight around the city. About 10 minutes after takeoff, he heard a loud “bang,” and the engine began to vibrate. Shortly thereafter, the engine lost power completely. The pilot made a gear-down forced landing on an interstate highway. During the landing roll, the airplane struck a vehicle and highway divider. Postaccident examination revealed both wings were bent. In addition, a hole was observed on the top of the engine crankcase, and the cylinder Nos. 5 and 6 connecting rods were missing. An engine examination revealed a large amount of metal debris in the oil pan. The oil filter also contained metal chips and filings. Recovered fragments included portions of the two connecting rods, the corresponding rod caps, and the associated rod bolts and nuts. Two rod cap nuts were found loose in the oil pan without any portion of the associated rod cap bolts. In addition, one rod bolt retained by the connecting rod was recovered but did not have a nut on the threaded end. The other rod bolts exhibited mechanical damage, separated threaded portions, or were not located. Airplane maintenance records indicated that the engine had accumulated 1,296 hours since overhaul which was completed about 16 years prior to the accident. A maintenance entry dated September 13, 2012, indicated that the Nos. 1, 4 and 6 cylinders were removed and reinstalled due to low compression. It is not known if the connecting rods were removed at this time. According to the most recent annual inspection, completed on October 7, 2020, the engine had accumulated 396 hours since the removal and replacement of cylinder Nos. 1, 4, and 6. The No. 6 cylinder was replaced about 8 years and 396 hours time-in-service prior to the accident.