Robinson R44 N4504L accident near Last Chance, Colorado

Probable cause

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.

NTSB analysis

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.

Text from the NTSB. Open the NTSB docket for CEN19LA162 for the full record.