NTSB Identification: DEN87FA147.
The docket is stored on NTSB microfiche number 34126.
Nonscheduled 14 CFR
Accident occurred Friday, June 05, 1987 in CHOTEAU, MT
Probable Cause Approval Date: 08/31/1988
Aircraft: BELL 206L-1, registration: N4999N
Injuries: 4 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 EMS HELICOPTER WAS RETURNING TO GREAT FALLS, MT, ON 6/5/87 WHEN IT CRASHED. ITS OCCUPANTS HAD EARLIER PARTICIPATED IN A RESCUE SEMINAR AT MANY GLACIER, MT. THE WRECKAGE WAS NOT FOUND UNTIL 6/9/87. A VIDEO TAPE RECOVERED FROM THE WRECKAGE DISCLOSED THE HELICOPTER TO BE FOLLOWING A HERD OF BIG HORN SHEEP UP A 7000-FT MOUNTAIN SLOPE AND FLYING SLOWLY AT TREE-TOP LEVEL WHEN IT SUDDENLY YAWED TO THE RIGHT. TESTS MADE ON THE AUDIO PORTION OF THE VIDEO TAPE REVEALED MAIN/TAIL ROTOR RPM WAS AT 100% POWER UNTIL 3.5 SEC BEFORE END OF TAPE. AT THAT TIME MAIN/TAIL ROTOR RPM DROPPED TO 94%. EVIDENCE ALSO DISCLOSED HELICOPTER TO BE FLYING AT HIGH GROSS WEIGHT, HIGH DENSITY ALTITUDE, AND WITH A TAILWIND.

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

COLLECTIVE..EXCESSIVE..PILOT IN COMMAND

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

AIRCRAFT PERFORMANCE,YAWING MANEUVERS..EXCEEDED

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

ROTOR RPM..NOT MAINTAINED..PILOT IN COMMAND


Contributing Factors

TERRAIN CONDITION..MOUNTAINOUS/HILLY


Contributing Factors

IN-FLIGHT PLANNING/DECISION..IMPROPER..PILOT IN COMMAND


Contributing Factors

WEATHER CONDITION..TAILWIND


Contributing Factors

TERRAIN CONDITION..UPHILL


Contributing Factors

COMPENSATION FOR WIND CONDITIONS..NOT PERFORMED..PILOT IN COMMAND


Contributing Factors

DIVERTED ATTENTION..PILOT IN COMMAND


Contributing Factors

WEATHER CONDITION..HIGH DENSITY ALTITUDE


Contributing Factors

ALTITUDE..REDUCED..PILOT IN COMMAND


Contributing Factors

AIRSPEED..REDUCED..PILOT IN COMMAND

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