N1069ZBell 206B · 1979

On May 9, 2012, about 0850 eastern daylight time, a Bell 206B-III, N1069Z,impacted terrain near Flora, Indiana, while spraying a wheat field. The pilot, the sole occupant on board, was not injured. The helicopter was substantially damaged. The helicopter was registered to and operated by Townsend Aviation, Monticello, Indiana, under the provisions of 14 Code of Federal Regulations (CFR) Part 137 as an aerial application flight. Visual meteorological conditions prevailed at the time of the accident, and no flight plan had been filed. The local flight originated from a staging area near Flora, Indiana, approximately 0820.

The pilot reported that he had exhausted his chemical load in the middle of the spraying operation and returned to the staging truck to resupply. He then returned to the field to resume spraying. Approaching the field from the northeast at a 45-degree angle, he made a gradual climbing left turn to align the helicopter for a spray run to the east, climbing to an altitude of approximately 100 feet and slowing to about 40 mph. The wind was approximately 300 degrees at 10 mph. As he made the turn, the wind became a tailwind. The helicopter began to descend and settle from about 100 feet. The pilot attempted to maintain a level attitude while attempting to gain airspeed. The helicopter impacted the ground in a level attitude on an easterly heading. The main rotor blades flexed down and severed the tail boom. The helicopter nosed over and came to rest on its right side facing west.

The FAA Helicopter Flying Handbook (FAA-H-8083-21, Chapter 11, p. 11-13)states, “Vortex ring state” is an aerodynamic condition in which a helicopter may be in a vertical descent with 20 percent up to maximum power applied, and little or no climb performance. “Settling with power” occurs when the helicopter keeps settling even though full engine power is applied. Main rotor tip vortices generate drag and degrade airfoil efficiency. As long as the tip vortices are small, their only effect is a small loss in main rotor efficiency. However, when the helicopter begins to descend vertically, it settles into its own downwash, which greatly enlarges the tip vortices. In this vortex ring state, most of the power developed by the engine is wasted in circulating the air in a doughnut pattern around the rotor. A vortex ring state may be entered during any maneuver that places the main rotor in a condition of descending in a column of disturbed air and low forward airspeed. Airspeeds that are below translational lift airspeeds are within this region of susceptibility to settling with power aerodynamics. This condition is sometimes seen during quick-stop type maneuvers or during recovery from autorotation.

Conducive to a settling with power are hovering above ground effect altitude, specifically attempting to hover out of ground effect (OGE) at altitudes above the hovering ceiling of the helicopter; attempting to hover OGE without maintaining precise altitude control; pinnacle or rooftop helipads when the wind is not aligned with the landing direction, and downwind and steep power approaches in which airspeed is permitted to drop below 10 knots, depending on the type of helicopter.