On July 17, 2001, at approximately 1515 mountain daylight time, an Aerospatiale SA315B helicopter, N2128Z, was destroyed when it rolled over following an emergency autorotation near Cody, Wyoming. The commercial pilot, the sole occupant in the aircraft, received minor injuries. Geo-Seis Helicopters, Fort Collins, Colorado, was operating under Title 14 CFR Part 133. Visual meteorological conditions prevailed at the time of the accident. The long line operation originated from a remote landing zone approximately 45 minutes before the accident. No flight plan was filed. The pilot reported that he was starting his 27th move of geophysical drilling equipment for the day. He was increasing power to lift an engine and compressor when he heard two loud "pops." The engine lost power, but the pilot did not release the long line because his ground helper was underneath the load. He moved forward a short distance, and autorotated to a 45 degree hill side. The aircraft landed and immediately rolled on its side with the mast pointing down slope, which stopped the aircraft from rolling. The ground helper said that he saw "fire shooting out of the tailpipe" as the helicopter descended. Postaccident examination of the engine revealed that all the turbine blades had experienced an extreme over temperature condition. The density altitude was computed to be 9,205 feet. The pilot had approximately 5,510 hours of flight experience in SA315B Lamas.