This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed.

On August 3, 2006, about 1230 mountain daylight time, a Bell 206L-1, N5746N, landed hard during an emergency landing following a loss of engine power near Busby, Montana. The commercial pilot and the three passengers were not injured. The helicopter, which was registered to TS Aviation of Worland, Wyoming, and under the operational control of the Bureau of Indian Affairs (BIA), U.S. Department of the Interior (DOI), sustained substantial damage. Visual meteorological conditions prevailed and a company flight plan was filed for the local public use flight. The purpose of the flight was to perform aerial wildfire reconnaissance.

The pilot reported that the engine failed during performance of a power assurance check. Prior to beginning the power check, the pilot established straight and level flight at 90 knots and 8,000 feet msl (about 5,000 feet agl). He increased collective, the helicopter began to climb, and at approximately 8,300 to 8,400 feet msl and a torque reading of 95%, there was a loud grinding noise and the engine lost power. The pilot entered an autorotation. He had difficulty stabilizing the rotor RPM during the initial stages of the autorotation, but had established a steady-state autorotation prior to descending below 500 feet agl. During touchdown in an open field, the main rotor struck and severed the tail boom.