On September 11, 1993, an Air Tractor AT301 (registration N36613) was involved in an aviation accident near Deatsville, AL. Investigators recorded the probable cause as: WAS A CRACK IN NO.3 CYLINDER HEAD WHICH RESULTED IN THE LOSS OF ENGINE POWER. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During a ferry flight between aerial application sites, an engine lost power after backfiring. The pilot made an emergency landing in a field, striking a tree. Investigation found a cracked cylinder head.
Event
While in cruise flight between aerial application sites, the pilot reported that the engine backfired three times and then lost power. The pilot's attempts to restore full power were unsuccessful. The pilot selected an open field for an emergency landing. During the landing roll, the airplane struck a tree.
Investigation
During the aircraft examination, an engine run was accomplished using the installed airframe components and systems, but full power was not developed. The subsequent examination of the engine assembly revealed a crack in the number three cylinder head between the spark plugs.
Engine Examination
According to an engine overhaul facility, these types of cracks are common in old radial type engines.