On March 20, 2009, about 1600 mountain standard time, a Robinson R22 helicopter, N90764, sustained substantial damage when it collided with terrain while maneuvering near Prescott, Arizona. The commercial pilot and his passenger were not injured. The helicopter was registered to Airfotos LLC, Prescott, and operated by the pilot. Visual meteorological conditions prevailed, and no flight plan was filed for the local aerial photography flight conducted under Title 14 Code of Federal Regulations Part 91. The flight originated at 1540 from Ernest A. Love Field Airport, Prescott, Arizona. The pilot reported that he was maneuvering near a residential structure to allow his passenger to take photographs. He completed one left-hand circle around the property. For the second pass, he descended to about 50 feet above the ground "to get a better angle for the shot" and slowed to "about 40 to 50 KIAS." The pilot stated that as he "neared the end of the pass, I felt/heard something and immediately checked the gauges and saw the engine rpm and rotor rpm both decaying." The pilot added that "it may have been that what I felt/heard was a reaction to the downwind heading." The pilot further reported that "about the same time, the low rotor speed warning horn sounded and the low rotor speed warning light came on." The pilot immediately lowered the collective and increased power. However, "due to the low altitude, there really wasn't time for these actions to take effect." The helicopter was rapidly approaching higher terrain, and the pilot initiated a left turn to avoid large boulders and trees. He applied "up collective to try to cushion the impact." Subsequently, the helicopter impacted the terrain and rolled onto its left side. Examination of the helicopter by the pilot revealed that the tail boom separated from the fuselage. The pilot reported that at the time of the accident, the wind was from 210 degrees at 10 knots gusting to 15 knots. The closest airport located about 20 nautical miles to the west of the accident site reported at 1553, wind from 180 degrees at 7 knots variable from 150 to 210 degrees. Robinson Safety Notice SN-34, "PHOTO FLIGHTS – VERY HIGH RISK," states, in part: "While maneuvering, the pilot may lose track of airspeed and wind conditions. The helicopter can rapidly lose translational lift and begin to settle." After the helicopter was recovered to a salvage yard located in Phoenix, salvage personnel started the engine with it still mounted in the helicopter's airframe. The engine "ran fine," however, as "the cooling fan was rubbing against its shroud," the test was terminated without running the engine up to a higher power. Salvage personnel observed no mechanical problems with the engine.