On April 1, 2002, a North American T-6-AT6D (registration N7471C) operated by U.s. Aircraft Inc., Llc was involved in an aviation accident near Gainesville, GA. Investigators recorded the probable cause as: A loss of engine power following a supercharger bearing failure and subsequent collision with the ground while maneuvering for an emergency landing. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During touch and go landings, smoke appeared from the right engine cowling after takeoff, accompanied by rough engine sounds. The pilot turned left toward the airport; the aircraft was seen nose low before disappearing below treeline and colliding with terrain. Post-accident engine examination revealed damage to the supercharger assembly.
Accident Sequence
A pilot and a certified flight instructor were conducting a series of touch and go landings. After takeoff, smoke was observed streaming from the right lower section of the engine cowling. Witnesses also reported hearing a rough engine condition. At approximately the same time, the pilot initiated a left turn toward the airport. The airplane was last seen in a nose low attitude. It then disappeared below the tree line and collided with the ground.
Engine Examination
Post-accident examination of the engine revealed damage throughout the supercharger assembly. The supercharger impeller was not totally secure on the impeller shaft. The impeller shaft retainer nut was loose on its shaft. This nut, as well as the impeller shaft gear-teeth, showed signs of wear; the teeth were worn down and disfigured. Both the aluminum cover plate and the bottom of the impeller blades displayed circular scraping. Small pieces of metal were found throughout the engine. Disassembly of the oil filter revealed metal shavings throughout. No metal parts or gear teeth were found in the oil sump.