Introduction
On June 14, 2016, about 1550 Pacific daylight time, a Bell 206L-1 helicopter, registration N1076Y, was substantially damaged during an autorotative landing attempt near Bishop, California. The accident occurred following a loss of engine power during cruise flight. The private pilot and two passengers were not injured. The helicopter was operated by the pilot under Title 14 Code of Federal Regulations Part 91 and was owned by a private company. Visual meteorological conditions prevailed, and no flight plan was filed for the cross-country flight.
Flight History
The flight departed Corona Municipal Airport (AJO), Corona, California, at approximately 1320, destined for Mammoth Yosemite Airport (MMH), Mammoth, California. The pilot reported departing with 110 gallons of fuel and flew direct to General Wm. J. Fox (WJF), Lancaster, California, to avoid restricted airspace. After more than 2 hours of flight in 30-knot headwinds and turbulence, the pilot decided to land at Bishop Airport due to low fuel, with about 110 lbs (approximately 16 gallons) remaining. During descent from 12,000 feet mean sea level (msl), as the helicopter passed below 10,000 feet msl, the pilot reported hearing a "violent explosion in the engine compartment" and felt vibrations. An engine-out light illuminated, and the pilot initiated an autorotation. Two restart attempts were unsuccessful. The pilot stated he was "too high" in the last 2,000 feet and pulled the collective early to avoid landing in a crater, resulting in a hard impact that substantially damaged the tail boom.
Weather
A National Transportation Safety Board (NTSB) weather study indicated that multiple forecasts before departure showed a probability of high winds along the route. A National Weather Service Surface Analysis Chart depicted a thermal low-pressure system over southern Nevada with a trough extending northward, creating a 12-hectopascal pressure gradient across southern California, supporting strong wind gusts over mountainous regions. Winds aloft forecasts, valid at 1400, indicated west-southwest winds at 17 to 30 knots. An area forecast issued at 1245 forecast southwesterly winds at 20 knots gusting to 30 knots. Terminal Aerodrome Forecasts issued the morning of the flight indicated gusts up to 30 knots. At Bishop Airport near the accident time, weather was reported as wind from 280 degrees at 7 knots, clear skies, temperature 32°C, dewpoint -2°C, and barometric pressure 29.76 inHg.
Post-Accident Examination
The helicopter came to rest about 4 nautical miles from Bishop Airport in a slight nose-up attitude. A first responder reported the fuel tank was void of fuel. An FAA inspector noted the fuel pump circuit breakers were extended (OFF position). The pilot stated he flew with them ON and pulled them after the helicopter came to rest, a customary practice. Later, the fuel pump motors ran when the circuit breakers were cycled. The helicopter was transported to a facility in Rancho Cordova, California, for examination. The empennage had separated from the aft tailboom, and the tail rotor drive shaft showed rotational scoring. One tail rotor blade was bent and attached; the opposing blade separated at the root. Paint transfer markings were found on main and tail rotor blades. The fuel system consisted of two forward tanks (11 gallons each) and an aft tank (88 gallons), with a range extender providing 110 gallons usable. Fuel boost pumps operated normally when tested. Approximately 20 gallons of JET A fuel were drained from the sump post-accident. The fuel gauge indicated 40-50 lbs of fuel. Fuel consumption was calculated at about 35 gallons per hour, equating to approximately 88 gallons burned during the 2-hour 30-minute flight. Control continuity was verified for collective, cyclic, and tail rotor pedals.
Engine Examination
The engine, a Rolls Royce M250 C30P, was examined and test-run at the manufacturer's facility. Initial inspection revealed the N1 and N2 tach-generator drive gears rotated freely, and magnetic chip detectors were free of debris. The compressor inlet showed black residue but no debris. A leak test with 50 PSI of pressurized air revealed no leaks. Three test runs showed normal operation at ground-idle, flight-idle, max-continuous, and take-off power. Transient tests showed rapid power advancement without hesitation. Vibration measurements were within limits. Engine performance was 4.8% below new production standards due to a faulty anti-ice solenoid valve that had failed in the open position, which was designed to fail open.