History of Flight
On July 27, 2013, about 1255 mountain daylight time, a Robinson R44 II helicopter, registration N25WH, was substantially damaged after a loss of control and subsequent impact with terrain near Thompson Falls, Montana. The helicopter was registered to Zoot Helicopter I LLC and operated by Rocky Mountain Rotors. The certified commercial pilot received fatal injuries; one passenger sustained serious injuries, and a second passenger suffered minor injuries. Visual meteorological conditions prevailed for the aerial survey flight, conducted under 14 CFR Part 91. The flight departed Polson Airport about 2 hours prior to the accident, with the intended destination of Thompson Falls.
According to the passenger with minor injuries, the flight's purpose was to photograph power lines and wooden structures. The pilot occupied the right front seat, an associate operating video equipment occupied the left front seat, and the reporting passenger was in the left rear seat taking still photos. The helicopter began rotating clockwise, completing about 4 revolutions before impacting terrain in a steep, nose-down, right-bank attitude. There was no postcrash fire.
The left-front-seat passenger, interviewed 6 months later, stated the helicopter was flying straight and level prior to the spin, and he next remembered impacting a tree. He reported hearing the low rotor rpm warning horn before impact, similar to sounds heard during engine start, and did not recall adverse wind conditions.
Data from an onboard Sony Handycam HDR CX550 with GPS captured the accident sequence. The helicopter was initially observed about 8.5 nautical miles west-southwest of Thompson Falls, following utility poles. At 1251, the helicopter circled left around utility poles near a creek. After two more left circles, it re-established on a northeast heading at 1254:26 at 39 knots groundspeed. By 1255:00, groundspeed decayed to 30 knots; at 1255:02, the helicopter began yawing right as speed dropped to 22.6 knots. It completed a 360-degree spin by 1255:06 and continued spinning. Groundspeed fluctuated below 22.6 knots until data terminated. Just before impact, the pilot's feet are shown with the left pedal deflected forward. The helicopter struck trees about 1255:13.
Personnel Information
The 35-year-old pilot held a commercial certificate with rotorcraft-helicopter and instrument helicopter ratings, a certified flight instructor certificate for rotorcraft-helicopter and instrument helicopter, and private pilot privileges for airplane single-engine land. His logbook showed a total flight time of 3,299.5 hours, with 376.9 hours in the same make and model. His most recent FAA flight review was on July 24, 2013, and his second-class medical certificate was issued February 13, 2013, with no limitations.
Aircraft Information
The Robinson R44 II (serial number 10481, 2004 model) had a maximum gross weight of 2,500 pounds and an estimated weight at the time of 2,300 pounds. It was powered by a 245-horsepower Lycoming IO-540-AE1A5 engine. The last annual inspection was on July 8, 2013, at 786.2 hours; total time at the accident was 799 hours. Maintenance records also noted installation of fuel bladder tanks on December 27, 2012, complying with Robinson SB-78B.
Meteorological Information
An NTSB meteorological specialist reviewed weather conditions. Surface analysis showed a low pressure center near the Montana-Canada border and a stationary front extending southward. Station models in the region indicated clear skies with winds generally 10 knots or less. A composite radar mosaic at 1300 MDT showed no reflectivity near the accident site. The ASOS at Mullan Pass (KMLP), about 8 nm southwest, reported wind variable at 4 knots, 10 miles visibility, clear skies, temperature 19°C, dew point 2°C, altimeter 30.17 inHg. The RAWS station THAM8, about 10 miles east-northeast, reported at 1302: temperature 88°F, dew point 47.9°F, wind from 317° at 7.8 knots gusting to 17.4 knots. A WRF simulation estimated sustained winds of 2-16 knots from the southwest, with gusts near 20 knots. An Area Forecast Discussion noted afternoon winds approaching 25 knots, and a Red Flag Warning advised west winds 15-20 mph gusting to 30 mph. The pilot did not receive a DUAT or Lockheed Martin weather briefing; it is unknown if he obtained other preflight weather information.
Wreckage and Impact
On July 28, 2013, NTSB, FAA, Robinson Helicopters, and Lycoming examined the wreckage. The helicopter had impacted heavily forested terrain in a steep nose-low, right-bank attitude at 2,915 feet msl, coming to rest on its right side on a magnetic heading of 178°. All flight components were accounted for. A subsequent examination of the engine and airframe on July 30 revealed no anomalies that would have precluded normal operation.
Tests and Research
Functional testing of the main and auxiliary fuel tanks and instrument cluster was conducted on August 29, 2013. Both fuel quantity sending units and indicators functioned within factory specifications. The main fuel tank (30.5 US gallons) and auxiliary tank (17.2 US gallons) were dented but operational within tolerances.
Additional Information
The FAA Rotorcraft Flying Handbook describes unanticipated yaw/loss of tail rotor effectiveness (LTE) as an uncommanded yaw rate that can occur in single-rotor helicopters at airspeeds less than 30 knots, not related to maintenance malfunction. FAA Advisory Circular 90-95 notes that LTE can occur in high-power, low-airspeed environments with left crosswind or tailwind. Robinson Safety Notice SN-42 states that failure to apply proper pedal inputs in strong or gusty winds during low-speed flight may result in unanticipated yaw.
Medical and Pathological Information
An autopsy of the pilot on July 29, 2013, listed the cause of death as "blunt force injuries." Toxicological testing was negative for alcohol and drugs.