Accident Details
On August 2, 2024, about 2107 mountain daylight time, a Bell 407 helicopter, registration N20BH, was substantially damaged during an accident near Raft River, Idaho. The pilot and three passengers sustained minor injuries. The helicopter was operated as a public use aircraft in support of the United States Forest Service.
Flight Information
The flight was transporting three Helitack crew members from Gerlach, Nevada, to their base at Pocatello, Idaho, with intermediate stops at Winnemucca and Elko, Nevada. The pilot reported that the first two legs were uneventful, and the accident occurred on the final leg.
Sequence of Events
About 55 minutes after departure from Elko, the pilot observed the barrier inlet air filter light starting to flicker. The filter had been changed the week prior, so the pilot considered such an activation premature. The light then transitioned from flickering to on, and the pilot activated the filter bypass system by pressing the “FILTER” light switch. Due to arrival time restraints, the crew discussed diverting to Burley, Idaho for the night but ultimately decided to continue to Pocatello.
A few minutes later, the pilot noticed the engine Measured Gas Temperature (MGT) gauge starting to rise into the yellow band. In response, the pilot reduced power and began to descend. However, the MGT continued to rise, and at an altitude between 1,000 and 1,500 ft, it climbed past the gauge redline of 779° C. The pilot decided to make a precautionary power-on landing and began looking for a suitable landing area. While maneuvering toward a grass field, the engine began to indicate an overspeed condition.
Emergency Maneuver and Impact
The pilot raised the collective control twice to try to arrest the overspeed, but the engine did not respond. He then performed an autorotation into an adjacent corn field. Due to the unknown height of the corn, the pilot was unable to judge the best time to initiate the final pitch pull. The helicopter landed hard after dropping from about 5 ft. The main rotor transmission assembly separated from the helicopter during the impact and fell into the cabin compartment. All occupants were able to egress by themselves.