NTSB Identification: LAX92FA137.
The docket is stored on NTSB microfiche number 52250.
Accident occurred Wednesday, March 04, 1992 in MARICOPA, AZ
Probable Cause Approval Date: 12/09/1993
Aircraft: ROBINSON R22, registration: N8413Q
Injuries: 1 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

THE WRECKAGE WAS LOCATED ON FLAT DESERT TERRAIN ALONG A DIRECT COURSE LINE BETWEEN THE DEPARTURE & DESTINATION AIRPORTS. THE TAIL BOOM HAD SEPARATED IN FLIGHT. DAMAGE WAS CONSISTENT WITH A LOW 'G' EVENT RESULTING IN A RAPID RIGHT ROLL & SUBSEQUENT MAIN ROTOR BLADE STRIKE ON THE LEFT SIDE OF THE CABIN. THE DESIGN STRENGTH OF THE TAIL CONE'S ATTACHMENT POINTS WAS EXCEEDED. ACCORDING TO THE MANUFACTURER'S PAPER ON LOW 'G' MAST BUMPING, BOTH LATERAL CONTROL AND DAMPING IN ROLL ARE PROPORTIONAL TO G-LOAD; IN A TWO G PULLUP THEY BOTH DOUBLE, AND IN A ZERO G PUSHOVER THEY BOTH GO TO ZERO. WHEN THEY ARE ZERO, THE PILOT HAS NO LATERAL CONTROL, AND THE HELICOPTER HAS NO DAMPING IN ROLL. THE PILOT WAS REPORTEDLY KEENLY AWARE THAT ONE SHOULD NOT PLACE THE R22 INTO A NEGATIVE 'G' SITUATION, OR EVEN A LOW 'G' SITUATION, AND WAS VERY KNOWLEDGEABLE OF THE R22'S STRUCTURE AND SYSTEMS.

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

DESTRUCTIVE MAST BUMPING FOR AN UNDETERMINED REASON(S).

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