On June 1, 1999, about 1800 Alaska daylight time, a skid equipped Robinson R22 helicopter, N1929T, sustained substantial damage during takeoff, about 35 miles west of Glennallen, Alaska. The helicopter was being operated under Title 14, CFR Part 135, when the accident occurred. The certificated commercial pilot, and the sole passenger aboard, were not injured. Visual meteorological conditions prevailed, and company flight following procedures were in effect. The flight originated about 0930 from a private airfield approximately 35 miles west of Glennallen. During a telephone conversation with the National Transportation Safety Board investigator-in-charge on June 2, the pilot reported that he was conducting an on-demand charter flight for the State of Alaska, and that the passenger was a wildlife biologist employed by the State of Alaska. The pilot added that the purpose of this particular flight was to locate and retrieve electronic tracking collars that had been dropped by previously tagged moose. He said that the wildlife biologist had electronically tracked a collar located atop a 4,200 feet msl mountain. An uneventful landing and engine shutdown was made, and the biologist recovered the radio collar. The pilot stated that during a northerly departure, the rotor rpm dropped, and the low rotor warning horn sounded. He said that in an attempt to regain rotor rpm and arrest the decent, he rolled the throttle to the high position, increased collective pitch, and lowered the nose to gain airspeed. He said that the rotor rpm continued to decay, the helicopter impacted uneven terrain, and rolled over. The pilot stated: "I just got into a downdraft on takeoff." He added that there were no preaccident mechanical anomalies with the helicopter. The helicopter sustained substantial damage to the rotor system, and fuselage.