The pilot reported that, while en route, the Taylorcraft BC12-D’s engine sustained a partial loss of power.
He attempted to restore power by applying carburetor heat, adjusting the mixture, and checking the fuel control valve. The troubleshooting efforts were unsuccessful, and the airplane was unable to maintain altitude.
He descended into a wooded valley near Trojan, South Dakota, and conducted a forced landing into the treetops. The airplane came to rest inverted, sustaining substantial damage to the fuselage and both wings. The pilot and his passenger were not injured in the crash.
A post-accident examination of the wreckage revealed that the hold-down nuts on the right magneto were loose, and the magneto could rotate freely by hand.
A lead deposit was noted in the No. 1 cylinder top spark plug, however it was not found to inhibit the function of the spark plug. No other pre-impact mechanical malfunctions were identified.
A review of the airplane maintenance logbooks revealed that the last 100-hour inspection of the engine occurred on Oct. 6, 2023. The logbooks stated that during this inspection, the magnetos were timed, and the spark plugs were cleaned and gapped.
The last annual inspection was on Sept. 1, 2024, six days before the accident. According to the mechanic who conducted the last annual inspection, the ignition timing was checked, but he did not recall if he adjusted the magnetos. He also stated that the airplane had operated about five to 10 hours between the completion of the last annual inspection and the time of the accident.
Probable Cause: The partial loss of engine power due to a loose magneto and subsequent impact with terrain.
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This September 2024 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
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