Last Chance, CO, USA
N4504L
Robinson R44
The helicopter pilot was performing an agricultural application flight. He approached the field from the east and completed a survey of the area that he intended to spray about 100 ft above ground level (agl). After maneuvering around the area, he decided to complete the east-west spray passes on the south side of the field and work north in order to have a crosswind during the passes. While flying east about 100 ft and 50 knots, he initiated a right turn, and the helicopter descended. As the helicopter continued the right turn and passed through a southwest heading, the gusting wind from the northeast resulted in a tailwind condition. During the descent with full throttle applied, the main rotor rpm began to decrease. The pilot lowered the collective and pitched forward to gain airspeed, but the main rotor rpm continued to decrease. About 50 ft agl, he started to jettison the spray load and was unable to increase the rotor rpm; the helicopter subsequently impacted the ground and came to rest on its side resulting in substantial damage to the tailboom. A postaccident examination of the helicopter did not reveal any anomalies that would have precluded normal operation. The circumstances of the accident are consistent with a loss of main rotor rpm while descending with a tailwind, which resulted in an uncontrolled descent into terrain.
On June 8, 2019, at 1159 mountain daylight time, a Robinson R44 helicopter, N4504L, was substantially damaged when it was involved in an accident when it impacted terrain during a low altitude aerial application operation near Last Chance, Colorado. The commercial pilot sustained minor injuries. The helicopter was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight. After the accident, the pilot stated that the helicopter was loaded with about 50 gallons of herbicide and about 10 gallons of fuel and that he intended to spray a 20-acre pasture. He estimated that the wind was from the north-northwest about 10 to 12 knots when he departed; the wind was shifting toward the north. He reported that after takeoff the helicopter exhibited no performance issues. He reported that he completed a survey of the area that he intended to spray about 100 ft above ground level (agl), then noticed that the helicopter was "lacking performance" so he completed one spray pass into the wind and then jettisoned about 5 gallons of herbicide to increase the helicopter's performance characteristics. After circling around the area, he decided to complete the east-west spray passes on the south side of the field and work north, in order to have a crosswind during the passes. He added that he completed the circle and flew south at about 100 ft and 50 knots with a tailwind, then made a gradual 90° right turn to start the decent into the field. He stated that during the descent the rotor rpm started to decrease. He stated that he already had the throttle full open, so he lowered the collective and pitched forward to gain airspeed; the rotor rpm continued to decrease. About 50 ft agl he started to jettison the entire load and was unable to increase the rotor rpm; the helicopter impacted the ground with a forward speed of about 60 knots. The owner spoke with the pilot after the accident and he stated that the pilot was setting up to spray a thistle patch. The pilot banked the helicopter around to the right to start the spray first pass when the rotor rpm began to decay. The pilot tried to recover the rotor rpm but was unable to at such a low altitude. He added that the engine was already at full throttle, so the pilot jettisoned the load. The pilot thought he had enough forward speed to begin a climb but was unable. The helicopter came to rest on its right side in an open field. The tailboom and spray equipment separated during the accident sequence. The company's recorded GPS data revealed that the helicopter initially approached the field from the south and made one pass over the field about 15 ft agl. The helicopter completed a figure-eight maneuver on the north side of the field then looped around on the west side of the field and approached to the east. While heading east, the helicopter made another pass over the field about 5 ft agl. The helicopter made one final right turn back toward the south side of the field and headed west; the apex of the turn was about 100 ft agl. The helicopter descended and the flight track ended on the south corner of the field. The responding Federal Aviation Administration (FAA) inspector confirmed from the recorded weather report that the wind was from the northeast at the time of the accident. The inspector completed an examination of the wreckage which revealed no anomalies that would have precluded normal operation. FAA Helicopter Flying Handbook – Helicopter Performance "Headwinds are the most desirable as they contribute to the greatest increase in performance. Strong crosswinds and tailwinds may require the use of more tail rotor thrust to maintain directional control. This increased tail rotor thrust absorbs power from the engine, which means there is less power available to the main rotor for the production of lift."
The pilot's failure to maintain adequate main rotor rpm while descending with a tailwind during an aerial application maneuver, which resulted in an uncontrolled descent into terrain.
Source: NTSB Aviation Accident Database
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