Accident Details
On March 13, 2022, at about 1240 central daylight time, a Cessna 150M (registration N63246) was substantially damaged during an accident at Brodhead Airport (C37) in Brodhead, Wisconsin. The two pilots on board sustained minor injuries. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
The pilots reported successfully completing two visual approaches to runway 27 without issues. While on the downwind leg for a third approach, the engine began to vibrate violently and lost power. The pilots attempted a forced landing to runway 9. The airplane overshot the turf runway and nosed over, resulting in damage to both wings and the vertical stabilizer.
Engine Examination
Postaccident examination of the engine revealed that 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 cover. Examination of the rocker boss fracture surfaces using a stereomicroscope showed fatigue crack initiation at and progression from the rocker shaft bore hole.
Maintenance History
In 1996, the Federal Aviation Administration issued Airworthiness Directive (AD) 94-05-05 R1, requiring inspection of the cylinder rocker shaft bosses at the next engine overhaul or cylinder removal, whichever occurred first. This AD was prompted by a history of fatigue cracking and separation of cylinder rocker shaft bosses on the installed cylinders. A review of the aircraft's maintenance records indicated that compliance with the AD was not required for the installed cylinders because 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 identified one prior accident, occurring on June 27, 1998, that involved failure of rocker shaft bosses after the AD issuance.