On October 3, 1994, a Bell 47G2 (registration N5193B) was involved in an aviation accident near Decatur, IL. Investigators recorded the probable cause as: The disengagement of the transmission freewheeling unit due to broken roller springs. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
After completing a line patrol, a pilot experienced engine overspeed and descended. A hard autorotative landing on a road damaged the helicopter. Investigation found broken springs in the freewheeling unit caused disengagement.
Accident Details
A pilot reported that after finishing a line patrol, he initiated a climbing left turn to return to the airport. While at an estimated altitude of 50 to 75 feet above ground level, he heard an unusual sound, the engine began to overspeed, and the helicopter started to descend. The pilot responded by lowering the collective and entering an autorotation to execute a forced landing on a nearby road. The touchdown was hard, resulting in damage to the helicopter.
Investigation Findings
A postaccident examination of the helicopter's transmission revealed that 13 of the 32 roller springs inside the freewheeling unit were broken. This failure caused the freewheeling unit to become disengaged, leading to the loss of drive and the subsequent engine overspeed and descent.
Probable cause
The disengagement of the transmission freewheeling unit due to broken roller springs.