On January 4, 1985, a Piper PA-18-150 (registration N3575Z) was involved in an aviation accident near Rawlins, WY. Investigators recorded the probable cause as: The grinding off of nine consecutive teeth on the left magneto drive gear, which caused the spark plugs to fire out of sequence and resulted in engine power loss. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
An aircraft experienced engine power loss and substantial damage during an off-airport emergency landing while searching for coyotes. Post-accident examination revealed ground-off teeth on the magneto drive gear.
What happened
The aircraft lost engine power and sustained substantial damage during an emergency landing conducted away from any airport. The flight was being performed for the purpose of locating coyotes.
The investigation
A post-accident examination of the engine revealed that nine consecutive teeth on the left magneto drive gear had been ground off. This mechanical failure allowed the spark plugs energized by the left magneto to fire or spark out of proper sequence, leading to the loss of power.
Findings
The primary factor contributing to the accident was the substantial damage to the left magneto drive gear. The missing teeth disrupted the ignition timing, causing the engine to lose power unexpectedly during the flight.
Probable cause
The grinding off of nine consecutive teeth on the left magneto drive gear, which caused the spark plugs to fire out of sequence and resulted in engine power loss.
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