WPR21LA358

The accident flight occurred after a mechanic replaced the exhaust pushrod for the No. 1 cylinder. After takeoff and during the initial climb, the engine lost total power. The airplane sustained substantial damage during a forced landing in desert terrain. Postaccident examination of the engine revealed that the No. 5 connecting rod strap exhibited fracture signatures consistent with fatigue cracks in multiple areas. The connecting rod also exhibited signs of heat distress. The No. 5 connecting rod bearing was severely worn, deformed, flattened, and darkened, consistent with high heat exposure. The general heat tinting and damage on the bearing, connecting rod, and crankshaft journal indicated that the No. 5 connecting rod bearing likely experienced frictional heating from insufficient clearance between the bearing and the journal. The insufficient clearance could have been produced by excessive wear on the bearing or journal, bearing surface damage such as spalling, or insufficient lubrication.

On September 11, 2021, about 1300 Pacific daylight time, a Beech BE35-B33, N8983M, was substantially damaged when it was involved in an accident near Baker, Nevada. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that, before the flight, a mechanic replaced the exhaust pushrod for the No. 1 cylinder. The engine was ground tested at various power settings with no anomalies noted. The mechanic subsequently deemed the airplane safe to fly to the pilot’s home airport. The pilot reported that the airplane departed from a dirt runway and once a positive rate of climb and airspeed were attained, he raised the landing gear. As the landing gear retracted, he heard a “loud bang,” followed a loss of total engine power. The pilot stated that he was able to extend the landing gear and make a forced landing onto open desert terrain. During the landing roll, the nose landing gear and right main landing gear collapsed, resulting in substantial damage to the fuselage and right wing. Postaccident examination of the engine revealed two holes in the top of the engine crankcase at cylinder Nos. 5 and 6. No oil was indicated on the oil dipstick. The undercarriage of the airframe from the nose to the tail was covered in oil, as was the top portion of the cowling. The assemblies for cylinder Nos. 5 and 6, piston assemblies, connecting rod pieces, and bearing pieces were examined by the NTSB Materials Laboratory in Washington, DC. The examination revealed that portions of the No. 5 connecting rod exhibited a dark tint, consistent with exposure to high heat. The bearing for the No. 5 connecting rod was severely worn, deformed, flattened, and darkened, consistent with high heat exposure. The connecting rod strap was fractured into multiple pieces. One portion, the fracture area near the exterior surface exhibited rachet marks and curving crack arrest lines, consistent with fatigue. Another portion of the fractured strap exhibited relatively smooth fracture features with curving crack arrest lines and ratchet marks, which were consistent with fatigue. For both of those portions of the strap, the fatigue origins were located at the radius for the attachment bolt boss. Examination of the damaged connecting rod journals on the crankshaft revealed scoring, deposited material, and heat tint damage on the journal for the No. 5 connecting rod. Scoring and pitting damage was also observed on the journal for the No. 6 connecting rod. The remaining journals for the connecting rods and the main journals exhibited no damage.