CEN16LA249

The pilot had departed on a local flight. He reported that, about 15 minutes after takeoff and when the airplane was about 1,100 ft above ground level, he felt a vibration and heard a "bang." The engine subsequently began to lose power. The oil pressure dropped to zero, the pilot heard another "bang," and the propeller stopped turning. The pilot executed a forced landing to a pasture, which resulted in substantial damage to the airplane when the nose landing gear collapsed in soft ground. An engine examination revealed that the No. 4 connecting rod had separated from the crankshaft. However, all fracture surfaces sustained secondary mechanical damage, which precluded further examination. The last engine overhaul was accomplished about 25 years before the accident. The engine manufacturer recommended engine overhauls every 12 years; however, the operator was not required to comply with that recommendation because the airplane was operated under Part 91. Given the available information, the reason for the connecting rod failure could not be determined.

On June 14, 2016, about 0945 central daylight time, an Aero Commander model 100-180 airplane, N3718X, was substantially damage during a forced landing following a loss of engine power near Port Lavaca, Texas. The pilot was not injured. The airplane was registered to and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight. The pilot reported that he felt a vibration and heard a "bang" about 15 minutes after takeoff when the airplane was at 1,100 ft above ground level. The engine subsequently began to lose power. The oil pressure dropped to zero as the pilot heard another "bang" and then the propeller stopped turning. He executed a forced landing to a pasture, and the nose landing gear collapsed due to the soft ground. A postaccident airplane examination revealed that the engine mount was damaged. An engine examination determined that the No. 4 connecting rod had separated from the crankshaft. The connecting rod mating flanges common to the rod cap were fractured. A fragment of the bearing was partially extruded around the connecting rod. The rod cap was deformed. A mating portion of one connecting rod flange remained secured to the rod cap by the attachment bolt and nut. The opposite connecting rod flange was fragmented and deformed. The attachment bolt was fractured. The bolt shank exhibited necking adjacent to the fracture surface; the mating portion of the bolt and the nut were not recovered. Three bearing fragments were recovered; each fragment was deformed and appeared worn. All fracture surfaces sustained secondary mechanical damage which precluded further examination. A review of the airplane maintenance records by a Federal Aviation Administration inspector revealed that the most recent engine overhaul was accomplished about 25 years before the accident flight. The engine manufacturer recommended that all engine models be overhauled within 12 years of the "date they first entered service or of last overhaul" in order to "mitigate engine deterioration that occurs with age." However, an aircraft owner is not required comply with the engine manufacturer's recommended overhaul interval when operating under Part 91 unless the engine does not meet the requirements of an annual inspection.