Accident Sequence
During an aerial application flight, the pilot heard a rattling noise coming from the aft end of the helicopter. Shortly thereafter, he lost tail rotor authority and the helicopter entered a flat spin. The pilot attempted to execute a run-on landing, but the helicopter continued to spin until it collided with terrain.
Post-Accident Examination
A Federal Aviation Administration inspector examined the helicopter after the accident. The inspector noted that the cross-over support tube near the aft end of the tail boom was missing. Additionally, a crack was found on the tail boom left side frame tubes. Deposits of rust in the area suggested that the crack was pre-existing. The inspector thought that this structural condition would have added excessive stress to the airframe during turning maneuvers, causing the last spline coupling shaft to disconnect from the tail rotor gearbox as the tail boom flexed.
Maintenance History
A 50-hour maintenance inspection had been completed on the helicopter the day before the accident.