NTSB Factual Report

***This report was modified on June 13,2018. Please see the docket for this accident to view the original report.***

The helicopter pilot reported that he was performing an agricultural flight and was in a hurry to spray the field because of a previous 3-hour delay caused by a broken fuel truck.

The pilot reported that the weight of the helicopter was forty pounds under the helicopter's maximum gross weight, and "I approached the field with the understanding that I was heavier, and it was hotter and more windy than I originally planned for."

He reported that the helicopter was headed south, and the wind was from the southwest about 15 knots.

The pilot made a low altitude, low airspeed, left turn to the north, and the helicopter entered a nose low attitude and had a more rapid sink rate than he anticipated. The pilot aborted the turn and chose to maintain a southeast heading to utilize the crosswind to avoid powerline wires. He attempted to arrest the sink rate by increasing the collective, but the low rotor RPM horn sounded.

The helicopter impacted the ground and bounced, then it rolled onto its left side. The helicopter sustained substantial damage to the tailboom, and the main rotor system.

The nearest METAR was about 32 miles northwest at the time of the accident reported and the wind was from 230° at 9 knots gusting to 16 knots. The temperature was 88°F and the dew point was 20°F. The field elevation was 696 feet and the density altitude was 2,786 feet.

According to the Federal Aviation Administration (FAA) Helicopter Flying Handbook, FAA-8083-21A (pg. 2-4, para. 5), turns in a helicopter increase the load factor exponentially, ultimately increasing the power requirement that is necessary to maintain the helicopter's altitude. Left pedal turns increase the quantity of anti-torque produced by the tail rotor, by demanding additional power from the 245-brake horsepower engine. Pilot flight control inputs demanding more power than the engine is capable of producing, with respect to the atmospheric conditions, adversely affects the helicopters ability to sustain its altitude. Available engine power is directly correlated to main and tail rotor RPM. When the engine fails to produce the required power to sustain airspeed and altitude at high DA, the main rotor blades will exceed their critical angle of attack, consequently decreasing main rotor blade RPM.

According to the FAA Helicopter Instructor's Handbook, FAA-8083-4 (pg. 8-4, para. 5), If a pilot begins a landing approach with a 10 knot tailwind, at some time in the approach, the helicopter experiences a zero knot airspeed, which means a total loss of translational lift and thrust. In order to maintain the approach angle, more power must be added.

The pilot reported that there were no preaccident mechanical malfunctions or failures with the helicopter that would have precluded normal operation.

NTSB Probable Cause

The pilot's decision to maneuver an overgross weight helicopter at a low altitude and airspeed with a gusting tailwind, which resulted in a high descent rate and collision with terrain. Contributing to the accident was the pilot's self-induced pressure to complete the operations due to a delay before the operations began.