CEN22LA141

The pilots reported the engine began to vibrate and lose power while on the downwind leg in the traffic pattern. The pilot in the right seat took control and attempted to conduct a downwind forced landing to the runway, but the airplane’s flight path continued beyond the end of the runway into uneven terrain and the airplane nosed over. The airplane sustained substantial damage to both wings and the vertical stabilizer. Postaccident examination revealed the No. 1 cylinder rocker shaft bosses were fractured. Further examination of fracture surfaces with a stereomicroscope revealed fatigue crack initiation at and progression from the rocker shaft bore hole. In 1996, based on a history of fatigue cracking of cylinder rocker shaft bosses, the Federal Aviation Administration issued an airworthiness directive (AD) that required inspection of the cylinder shaft rocker bosses at the next overhaul or cylinder removal. Since the engine was last overhauled in 1978 and the No. 1 cylinder was last removed 1991, compliance with the AD was not required for the accident airplane’s No. 1 cylinder.

On March 13, 2022, about 1240 central daylight time, a Cessna 150M, N63246, was substantially damaged when it was involved in an accident at Brodhead Airport (C37), Brodhead, Wisconsin. The two pilots sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilots reported that they flew two visual approaches without incident to runway 27 at C37. While on downwind for a third approach, the engine began to vibrate violently and lost power. The pilots attempted a forced landing to runway 9. The flight path continued beyond the end of the turf runway and the airplane nosed over, which resulted in damage to both wings and the vertical stabilizer. During the postaccident examination of the engine the No. 1 cylinder valve rocker cover was removed and the two rocker arms, pivot shaft, and pieces of the cylinder shaft rocker bosses came off freely with the rocker cover. Examination of the rocker boss fracture surfaces with the aid of a stereomicroscope revealed fatigue crack initiation at and progression from the rocker shaft bore hole. In 1996, the Federal Aviation Administration issued an AD 94-05-05 R1 that required inspection of the cylinder rocker shaft bosses at the next engine overhaul or cylinder removal, whichever occurred first. The AD was issued based on a history of fatigue cracking and separation of cylinder rocker shaft bosses of the installed cylinders. A review of maintenance records indicated the AD was not required to be complied with for the installed cylinders since the engine was last overhauled in 1978 and the No. 1 cylinder was last removed in 1991. A search of previous National Transportation Safety Board reports revealed one accident after the AD issuance that involved failure of rocker shaft bosses. This accident occurred on June 27, 1998.