On September 7, 1994, a Cessna 172M (registration N61838) was involved in an aviation accident near Coolin, ID. Investigators recorded the probable cause as: The rocker arm failed due to fatigue cracking initiated at rough tool marks produced during chamfering of the arm's oil hole by the engine manufacturer during remanufacture. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A private pilot performed a forced landing after losing engine power. The aircraft struck a tree stump and nosed over, sustaining substantial damage. Investigation found the No. 1 cylinder exhaust valve rocker arm failed due to fatigue from tool marks made during engine remanufacture.
Accident Overview
A private pilot was forced to land an airplane on unsuitable terrain due to a loss of engine power. During the forced landing, the airplane impacted a tree stump, nosed over, and sustained substantial damage.
Engine Examination
An examination of the engine revealed that the rocker arm for the No. 1 cylinder exhaust valve had failed. Further examination of the rocker arm determined that the failure was due to fatigue. The fatigue cracking was initiated at rough tool marks produced during the chamfering of the arm's oil hole. This chamfering was performed by the engine manufacturer during remanufacture of the engine.
Conclusion
The investigation identified the failure of the exhaust valve rocker arm as the cause of the engine power loss. The fatigue cracks originated from tool marks introduced during the manufacturing process.
Probable cause
The rocker arm failed due to fatigue cracking initiated at rough tool marks produced during chamfering of the arm's oil hole by the engine manufacturer during remanufacture.
What happened in the 7 Sept 1994 Cessna 172M accident near Coolin, ID?
A private pilot performed a forced landing after losing engine power. The aircraft struck a tree stump and nosed over, sustaining substantial damage. Investigation found the No. 1 cylinder exhaust valve rocker arm failed due to fatigue from tool marks made during engine remanufacture.
What aircraft was involved and where did it happen?
The accident on 7 Sept 1994 involved a Cessna 172M, registration N61838, at Coolin, ID.
What was the probable cause of the accident?
The rocker arm failed due to fatigue cracking initiated at rough tool marks produced during chamfering of the arm's oil hole by the engine manufacturer during remanufacture.
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