The pilot reported that, while the Piper PA-25-235 was towing a banner about 1,100 feet mean sea level, the engine lost power.
His attempts to restart the engine were unsuccessful.
He executed a forced landing to a pasture in Galveston, Texas, during which the right wing struck a fence. The airplane then came to rest upright. The pilot was seriously injured in the crash.
Disassembly of the engine revealed that a crankshaft idler gear shaft had failed and separated from the accessory gear case. The failed idler gear shaft and its attachment hardware were not located, and a metallurgical examination could not be conducted to determine the reason for the failure.
Probable cause: The loss of engine power due to a failure of a crankshaft idler gear shaft.
NTSB Identification: CEN15LA297
This June 2015 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.