BELL 407

Full Narrative

On August 2, 2024, about 2107 mountain daylight time, a Bell 407, N20BH, was substantially damaged when it was involved in an accident near Raft River, Idaho. The pilot and the three passenger’s sustained minor injuries. The helicopter was operated as a public use aircraft flight in support of the United States Forest Service.

The flight was for the transportation of 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 that the accident occurred on the final leg.

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 he thought such an activation was 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 then discussed the option of diverting to Burley, Idaho for the night. They ultimately decided to continue to Pocatello, and a few minutes later the pilot noticed the engine Measured Gas Temperature (MGT) gauge starting to show a 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 continued to climb 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. However, as he was maneuvering the helicopter towards a grass field, the engine began to indicate an overspeed condition.

The pilot raised the collective control twice to try to arrest the overspeed, but the engine did not respond so he decided to perform to 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, and the helicopter landed hard after dropping from about 5 ft.

The main rotor transmission assembly was separated from the helicopter during the impact and dropped down into the cabin compartment. All occupants were able to egress by themselves.