On June 26, 2003, a Cessna 150F (registration N8517G) was involved in an aviation accident near Williamson, NY. Investigators recorded the probable cause as: The failure of a rocker arm shaft boss, which resulted in a partial loss of power and subsequent forced landing. A factor was the unsuitable terrain. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During a training climb, the engine ran rough. The CFI took control and performed a forced landing to an apple orchard. Both wings struck trees. Investigation revealed a fatigue fracture of the number one cylinder rocker shaft boss. The last engine overhaul was in 1977, while an AD requiring inspection was issued in 1994.
Incident
A training flight experienced an engine malfunction during the climb. The student pilot was at the controls when the engine began running roughly. The certified flight instructor (CFI) assumed control and decided to execute a forced landing in an apple orchard. During the landing, the left and right wings struck trees, and the airplane subsequently came to rest in an upright position.
Investigation
Examination of the engine disclosed a fractured cylinder rocker shaft boss on the number one cylinder. The fracture exhibited characteristics consistent with fatigue.
Airworthiness Directives
An Airworthiness Directive (AD) was published in 1994, requiring maintenance personnel to inspect the cylinder rocker shaft bosses for cracks. The inspection was to be performed at the next cylinder removal from the engine or engine overhaul, whichever occurred first, after the effective date of the AD. A revised AD became effective in 1996. A review of the airplane's engine maintenance records showed that the last engine overhaul and cylinder removal had been accomplished in 1977.