Incident Description
While the helicopter was in cruise flight at 800 feet, the pilot perceived a high-frequency shudder accompanied by a growling sound. The shudder intensified, and the helicopter yawed to the right. The pilot executed an autorotation. Upon touchdown on water, the main rotor blades struck and severed the tail boom, causing the helicopter to roll to the right and partially submerge.
Postcrash Examination
Inspection after the accident revealed that the tail rotor gearbox and tail rotor assembly had separated from the airframe and were not recovered. Evidence of damage indicated that the tail rotor gearbox had been loose from its mounting for an extended period prior to the accident.
Maintenance History
Maintenance records showed that the tail rotor gearbox input seal had been replaced 110 flight hours before the accident. Additionally, during a 100-hour inspection conducted 14 flight hours before the accident, a mechanic certified that the tail rotor gearbox attach bolts had been checked for proper torque.
Operational Procedures
Bell Helicopter operating procedures mandate that the tail rotor and tail rotor gearbox be inspected during the pilot's preflight check. The extent to which this inspection was performed prior to the flight is not specified in the available records.