NTSB Identification: LAX99LA004.
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Accident occurred Sunday, October 04, 1998 in MOORPARK, CA
Probable Cause Approval Date: 09/28/2000
Aircraft: Burson REVOLUTION MINI 500, registration: N418MB
Injuries: 1 Fatal.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The helicopter did not return from an afternoon local area flight and the wreckage was located early the following morning. Both main rotor blades, the tail rotor assembly, the tail boom, and a section of the tail rotor drive shaft were found in a debris field approximately 1/8 mile from the fuselage wreckage. Both main rotor blades separated from the hub outboard of the root doubler and exhibited leading edge damage near the tip and downward bending. Additionally, the 'A' blade was bent smoothly aft approximately 30 degrees over its span. The tail boom was separated from the fuselage approximately 2 feet forward of the tail rotor gearbox. The separation exhibited a diagonal slicing appearance from upper forward to lower aft on the boom. The tail rotor drive shaft was separated at the same fuselage station as the tail boom, and the shaft had a dented appearance which resembled the leading edge radius of the main rotor blade. The main rotor mast exhibited a mast-bumping dent on one side of the mast at the hub attachment but no similar dent on the opposite side. Examination of the aircraft did not reveal any mechanical malfunction of the engine or flight control system.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The improper use of the cyclic flight control by the pilot, which resulted in low g flight load condition, which resulted in rotor disk divergence (mast bumping), and the main rotor blade striking and severing the tail boom. Full narrative available
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