Accident Details
On July 12, 2015, at about 1300 mountain daylight time, a Robinson R22 Beta II helicopter, registration N441MM, was substantially damaged when it collided with rising terrain approximately 10 miles west of Escalante, Utah. The helicopter was registered to Cornerstone Management of Newark, Delaware, and operated by the pilot as a personal flight under 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The helicopter had departed from private property near Escalante around 1230.
The pilot sustained serious injury, and his passenger sustained minor injury.
Pilot's Account
According to the pilot, after refueling at a friend's property, he departed and flew up a canyon while climbing over rising terrain. He noticed a substantial tailwind gust, and the helicopter's airspeed decreased below Effective Translational Lift (ETL), causing the helicopter to stop climbing. The pilot immediately made a left turn intending to reverse course and turn into the wind. After turning approximately 90 degrees, he noticed a change in engine noise and heard the Low Rotor RPM Warning Horn. He lowered the collective to regain rotor rpm while continuing to turn, but the helicopter was about 50 ft above ground level (AGL). He was unable to recover rotor rpm, and the helicopter impacted the terrain. The helicopter came to rest on its left side facing west.
Environmental Factors
The accident site elevation was 7,461 ft. The temperature was 75°F. Pressure altitude (PA) was 7,011 ft, and density altitude (DA) was 9,600 ft.
Weight and Balance
The calculated gross weight at the time of the accident was 1,400.42 lb. The Robinson R22 Pilot Operating Handbook (POH) lists a maximum allowable gross weight of 1,370 lb. At 7,011 ft PA and 75°F, the maximum allowable weight per the POH is 1,275 lb.
Performance Considerations
According to the R22 POH, the helicopter was capable of in-ground-effect (IGE) flight at maximum gross weight (1,370 lb) at 75°F up to 7,800 ft PA. The maximum out-of-ground-effect (OGE) capability under those conditions was 3,500 ft PA. The pilot reported airspeed below ETL and altitude approximately 50 ft AGL when turning, conditions that fall within the avoid region of the Height/Velocity Diagram. The POH states that pilots should avoid operating below 24 KIAS at altitudes between 10 and 50 ft AGL; at altitudes above 7,000 ft DA and weight 1,300 lb, the avoid region extends from 10 to 510 ft AGL.
Additional Information
The FAA Helicopter Flying Handbook notes that turns increase load factor, raising power requirements. Left pedal turns require additional anti-torque power from the engine. At high density altitude, available power is reduced, and if the engine cannot meet demand, main rotor rpm decreases. The handbook also states that tailwinds below 30 knots can increase tail rotor thrust demand, reducing power available to the main rotor. At high altitudes, tail rotor efficiency is reduced, increasing the risk of loss of tail rotor effectiveness (LTE). The pilot was operating with a tailwind and made an immediate left turn, conditions that can lead to LTE in the regions of Weathercock Stability and Tail Rotor Vortex Ring State.