On May 23, 1993, a Cessna 185A (registration N4080Y) operated by Forbes, Clarence, R. was involved in an aviation accident near Lowell, ID. Investigators recorded the probable cause as: Fatigue separation of the number two cylinder exhaust rocker arm, which had been installed without an approved STC. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During cruise at 8,000 feet, the aircraft experienced a partial power loss. The pilot observed oil on the left wing strut and performed a precautionary landing in a field. During the landing roll on soft terrain, the aircraft nosed over. Investigation revealed a fatigue-fractured rocker arm installed without an approved STC.
Accident Sequence
While flying at an altitude of 8,000 feet MSL, the aircraft experienced a partial power loss. The pilot noticed oil on the left wing strut and, to prevent engine seizure, chose to execute a precautionary landing in a field. During the landing roll, the aircraft encountered soft terrain and nosed over.
Examination Findings
Post-crash examination revealed that the number two cylinder exhaust rocker arm was broken in half. A metallurgical examination determined that the rocker arm separated due to fatigue. The rocker arms in the engine were not covered by an approved Supplemental Type Certificate (STC) and had been installed approximately 11 hours before the accident.
Probable cause
Fatigue separation of the number two cylinder exhaust rocker arm, which had been installed without an approved STC.
Frequently asked questions
What happened in the 23 May 1993 Cessna 185A accident near Lowell, ID?
During cruise at 8,000 feet, the aircraft experienced a partial power loss. The pilot observed oil on the left wing strut and performed a precautionary landing in a field. During the landing roll on soft terrain, the aircraft nosed over. Investigation revealed a fatigue-fractured rocker arm installed without an…
What aircraft was involved and where did it happen?
The accident on 23 May 1993 involved a Cessna 185A, registration N4080Y, operated by Forbes, Clarence, R., at Lowell, ID.
What was the probable cause of the accident?
Fatigue separation of the number two cylinder exhaust rocker arm, which had been installed without an approved STC.
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