LAX05LA155 · Bell 206L-1

The helicopter descended to ground impact following an interruption of power while performing a long line sling load operation. The purpose of the flight was to sling load fuel cans from a landing strip that is located on the rim of the Grand Canyon to the canyon floor directly below to refuel the tour boats operating on the Colorado River. The accident flight was the first flight of the day. The pilot utilized a 50-foot-long line and a net to transfer 15 fuel cans down to the canyon floor. The pilot said that when he picked up the load at the top of the canyon (elevation 4,800 feet msl) he performed a power check and the torque required was 75 percent for an out of ground effect hover. After stabilizing the load he began a descent to the canyon floor below (at an elevation of 1,300 feet msl) and was at a descent rate of about 50 feet per minute as he neared the ground. The wind conditions were reported by witnesses and the pilot as being calm, or nearly so. His head was outside the cockpit watching the ground crew, when he heard a tone, and then heard a series of three low frequency popping noises. The pilot said he was unsure if the popping sounds were coming from the engine or from the main rotor blades The helicopter then began to settle toward the ground and descended to a hard impact into desert scrub brush. The pilot said he closed the throttle after hearing popping noises and entered an autorotation. Witnesses to the accident reported that the approach was a controlled approach, and there was no sway or other unusual movement in the load. As a ground crewmember reached for the load, about 5 feet above the ground, he saw the helicopter sink down and impact the scrub brush and the ground. The witness did not perceive any unusual popping sounds preceding the descent and impact. The Rolls-Royce 250-C30P engine was removed from the airframe shipped to a repair facility with a test cell. There were no significant irregularities noted in the engine test cell runs that were conducted. Both the power turbine governor and gas producer fuel control were tested at the manufacturer's facilities and there were no conditions identified that would have prevented normal operation of either unit.

Verbatim NTSB analysis and probable cause from the NTSB dataset