CEN12LA359 · Robinson Helicopter Company R44 II

The helicopter was about 76 pounds under its maximum gross weight for the takeoff at a density altitude of about 6,800 feet. The pilot lifted the helicopter into a hover 2 feet above ground level (agl) and departed into the wind, which was variable from 210-260 degrees at 10 knots, gusting to 18 knots. After the helicopter entered translational lift, the pilot accelerated the helicopter to 30-35 knots and climbed to about 10-20 feet agl. The helicopter suddenly started to settle, the low rotor rpm warning light illuminated, and the warning horn sounded. The left seat passenger, who was a flight instructor, took control of the helicopter and attempted to recover rotor rpm. Unable to regain enough rotor rpm to maintain flight, he decided to land under control rather than continue to an uncontrolled crash. He was only able to slow the helicopter to about 15-20 knots before leveling the helicopter to land. The helicopter touched down in rough, uneven terrain, and substantial damage was incurred to the fuselage and tailboom. Examination of the helicopter did not show any evidence of preimpact mechanical malfunctions or failures that would have resulted in the loss of main rotor rpm and settling.

The pilot and the left seat passenger stated that they could have operated the helicopter at a lighter takeoff weight for greater performance or waited until early morning to depart when the cooler temperatures would have reduced the density altitude. Further, they stated that the wind gusts resulted in the loss of some of the headwind component. Additionally, the left seat passenger reported that at the time the helicopter began to settle, a freight train was crossing about 30 to 50 yards in front of the takeoff flight path of the helicopter. He stated that he believed the train probably blocked some of the headwind component as it passed. A reduction in the headwind component would have resulted in the helicopter settling at a critical point during the takeoff. The pilot and the left seat passenger stated that the collective was probably raised slightly to compensate for the settling, which caused the decay of main rotor rpm, and once that happened, the helicopter was in a position that was not recoverable.

Given that the settling was sudden during an otherwise routine takeoff, it is likely that a wind gust, the blocking of the wind by the passing train, or a combination of the two resulted in an abrupt decrease in headwind, which caused the helicopter to lose lift and descend. Because the helicopter was already operating near its maximum performance capability (high gross weight at high density altitude), there was not enough reserve power available to stop the descent and maintain rotor rpm.

Verbatim NTSB analysis and probable cause from the NTSB dataset