Accident Overview
On June 8, 2019, at 1159 mountain daylight time, a Robinson R44 helicopter, registration N4504L, was substantially damaged when it impacted terrain during a low-altitude aerial application operation near Last Chance, Colorado. The commercial pilot sustained minor injuries. The helicopter was operating under Title 14 Code of Federal Regulations Part 137 as an aerial application flight.
Pilot Account
According to the pilot, the helicopter was loaded with approximately 50 gallons of herbicide and about 10 gallons of fuel for a planned spray of a 20-acre pasture. He estimated the wind at departure to be from the north-northwest at 10 to 12 knots, shifting toward the north. After takeoff, no performance issues were noted. The pilot conducted a survey of the area at about 100 ft above ground level (agl) and noticed the helicopter was "lacking performance." He completed one spray pass into the wind and jettisoned about 5 gallons of herbicide to improve performance. Circling the area, he decided to make east-west passes on the south side of the field and work north for a crosswind. He flew south at about 100 ft and 50 knots with a tailwind, then made a gradual 90° right turn to descend into the field. During the descent, rotor rpm began to decrease. With the throttle already full open, he lowered the collective and pitched forward to gain airspeed, but rotor rpm continued to drop. At about 50 ft agl, he jettisoned the entire load, but could not increase rotor rpm, and the helicopter impacted the ground at a forward speed of about 60 knots.
Owner's Statement
The owner spoke with the pilot after the accident. The pilot stated he was setting up to spray a thistle patch and banked the helicopter right to start the first pass when rotor rpm decayed. He tried to recover but was unable at low altitude. With the engine at full throttle, he jettisoned the load. He thought he had enough forward speed to climb but could not.
GPS Data
Recorded GPS data from the company showed the helicopter initially approached the field from the south, making one pass about 15 ft agl. It then completed a figure-eight maneuver on the north side, looped around the west side, and approached east. While heading east, it made another pass about 5 ft agl. A final right turn back toward the south side heading west followed, with the turn apex at about 100 ft agl. The helicopter descended, and the flight track ended at the south corner of the field.
Examination
The responding Federal Aviation Administration (FAA) inspector confirmed from a recorded weather report that the wind was from the northeast at the time of the accident. An examination of the wreckage revealed no anomalies that would have precluded normal operation.
FAA Helicopter Flying Handbook Excerpt
The FAA inspector referenced the Helicopter Flying Handbook section on Helicopter Performance, which states: "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."