Accident Overview
On September 2, 2023, at about 1100 eastern daylight time, a Beech V35 airplane, registration N5431U, was substantially damaged in an accident near Rutledge, Tennessee. The airline transport pilot and a passenger were not injured. The flight was operated as a personal flight under Title 14 Code of Federal Regulations Part 91.
Flight History
The pilot reported departing Gatlinburg/Pigeon Forge Airport (GKT), Sevierville, Tennessee, around 1045. The airplane climbed to 2,500 ft mean sea level and proceeded northbound. Approximately 15 minutes into the flight, over a forested area, the engine emitted a loud bang and began running rough. The pilot turned to a southerly heading toward an open field, but the engine seized. Unable to reach the field, the pilot performed a forced landing into trees. The wreckage came to rest inverted, and first responders met the pilot and passenger.
Wreckage and Engine Examination
Federal Aviation Administration inspectors examined the wreckage. There was no fire. The fuselage, wings, and empennage sustained substantial damage. The external fuselage surfaces were covered with engine oil.
After recovery, the engine was removed for examination. Several small holes (about 0.75 inch) were found in the upper engine case, and one large hole was located under the area of the left magneto. The oil pan contained engine oil and numerous metallic fragments.
Further disassembly revealed that one of the No. 2 crankshaft cheek counterweights was missing. The largest hole in the engine case was directly adjacent to the area where the counterweight had liberated. Retaining circlips and plates from the counterweight were found inside the engine. Two circlips were fractured, and two were bent but intact.
Circlip Analysis
The circlips and plates were sent to the NTSB Materials Laboratory. Circlips were numbered 1 through 4. Circlips 1 and 2 were intact and bent. Circlip 3 was fractured at both leg ends; the fractures showed localized necking and cup-shaped surfaces consistent with overstress. Circlip 4 also had both leg ends fractured. One fracture resembled those in circlip 3, while the other exhibited two thumbnail-shaped cracks along the inner surface with fatigue striations consistent with fatigue crack propagation.
Maintenance Records
A review of the aircraft maintenance records showed that the engine was disassembled and inspected for a propeller strike on November 2, 2020, at 5,061 total airframe hours. The airplane had accrued about 130 hours since that inspection.