Bell 47G-3B-1 N24SD accident near Denio, Nevada

Probable cause

The pilot's inadvertent hard landing induced by a perceived loss of power and a main transmission anomaly while maneuvering at low altitude.

NTSB analysis

After the passenger shot a coyote during the predator control flight, the helicopter pilot circled the injured coyote. While maneuvering at 15 miles per hour and about 20 feet above the hilly terrain, the pilot heard a grinding noise, which he opined originated from the transmission. The pilot believed the helicopter was losing power, and he opted to immediately land on sloping terrain. The helicopter touched down hard, the main rotors severed the tail boom, and the helicopter rolled over. During the subsequent examination of the airframe, transmission, and engine, no evidence of a mechanical malfunction was found. One of the two cooling fan drive belts was not found seated, and may have rolled over on its pulley, producing the noise that the pilot may have misinterpreted as relating to a loss of power.

Text from the NTSB. Open the NTSB docket for LAX08LA097 for the full record.