Incident Overview
On June 5, 1987, an EMS helicopter was returning to Great Falls, Montana, when it crashed. The helicopter's occupants had earlier participated in a rescue seminar at Many Glacier, Montana. The wreckage was not located until June 9, 1987.
Video Evidence
A video tape recovered from the wreckage revealed that the helicopter was following a herd of big horn sheep up a 7000-foot mountain slope and flying slowly at tree-top level. The footage showed the helicopter suddenly yawing to the right.
Rotor RPM Analysis
Tests conducted on the audio portion of the video tape indicated that main/tail rotor RPM was at 100% power until 3.5 seconds before the end of the tape. At that point, main/tail rotor RPM dropped to 94%.
Flight Conditions
Evidence disclosed that the helicopter was flying at high gross weight, high density altitude, and with a tailwind.
Conclusion
The circumstances of the crash are documented through video and audio evidence, as well as operational conditions. No probable cause was stated in the source.