NTSB Identification: LAX89LA253.
The docket is stored on NTSB microfiche number 40023.
Accident occurred Monday, July 31, 1989 in RIALTO, CA
Probable Cause Approval Date: 03/29/1991
Aircraft: Bell 206B, registration: N10857
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

DURING A PRACTICE AUTOROTATION WITH A POWER RECOVERY, THE FLIGHT INSTRUCTOR HEARD A NOISE FROM THE REAR OF THE HELICOPTER. WHEN THE POWER RECOVERY WAS ATTEMPTED, THE ENGINE RESPONDED TO THE THROTTLE APPLICATION BUT THE LOW RPM WARNING HORN ACTIVATED AND THE HELICOPTER STRUCK THE GROUND IN A LEVEL ATTITUDE WHICH CAUSED THE MAIN ROTOR BLADES TO SEVER THE TAILBOOM. EXAMINATION OF THE HIGH SPEED OUTPUT DRIVESHAFT COUPLING, TRANSMISSION END, SHOWED THAT THE FOUR BOLTS WERE INSTALLED BUT THE FOUR NUTS AND FOUR WASHERS COULD NOT BE FOUND IN THE ASSEMBLY. TWO NUTS WERE FOUND IN THE SCUPPER DRAIN OF THE TRANSMISSION DECK.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

FAILURE TO INSTALL TWO OF THE FOUR REQUIRED NUTS WHICH RETAIN THE HIGH SPEED COUPLING INPUT DRIVE SHAFT TO THE TRANSMISSION.

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