Accident Details
On May 9, 2012, at approximately 0850 eastern daylight time, a Bell 206B-III helicopter, registration N1069Z, impacted terrain near Flora, Indiana, while spraying a wheat field. The pilot, the sole occupant, was not injured. The helicopter was substantially damaged. The flight was conducted under 14 Code of Federal Regulations Part 137 as an aerial application operation and was operated by Townsend Aviation of Monticello, Indiana. Visual meteorological conditions prevailed, and no flight plan had been filed. The local flight originated from a staging area near Flora at about 0820.
Flight Sequence
The pilot reported that after exhausting his chemical load during a spraying operation, he returned to the staging truck to resupply and then returned to the field. Approaching from the northeast at a 45-degree angle, he made a gradual climbing left turn to align the helicopter for an eastward spray run, climbing to approximately 100 feet and slowing to about 40 mph. The wind was from 300 degrees at 10 mph. As he turned, 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 trying 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, and the helicopter nosed over, coming to rest on its right side facing west.
Aerodynamic Considerations
The FAA Helicopter Flying Handbook (FAA-H-8083-21, Chapter 11, p. 11-13) describes vortex ring state as an aerodynamic condition where a helicopter may be in a vertical descent with 20 percent up to maximum power applied, with little or no climb performance. Settling with power occurs when the helicopter continues to descend even with full engine power. Main rotor tip vortices generate drag and degrade airfoil efficiency. When descending vertically into its own downwash, tip vortices enlarge, wasting engine power in circulating air around the rotor. This condition can be entered during maneuvers that place the main rotor in descending conditions with low forward airspeed, such as quick stops or autorotation recovery.
Conditions conducive to settling with power include hovering above ground effect altitude, attempting to hover out of ground effect (OGE) above the helicopter's hovering ceiling, failing to maintain precise altitude control during OGE hovering, and conducting downwind or steep power approaches where airspeed drops below 10 knots, depending on helicopter type.