Summary
On October 22, 2013, about 0605 central daylight time, a Eurocopter AS 350 B3, N353HW, struck trees and terrain near Somerville, Tennessee. The helicopter was destroyed by impact and a post-crash fire. The commercial pilot, a registered nurse, and a respiratory therapist were fatally injured.
History of Flight
The helicopter was operated by Memphis Medical Center Air Ambulance Service, doing business as Hospital Wing, on a positioning flight under 14 CFR Part 91. It departed Hospital Wing Heliport (2TN0), Memphis, Tennessee at 0547, en route to Whitehurst Field Heliport (60TN), Bolivar, Tennessee. Earlier that day, the pilot had aborted a flight due to low ceilings and declined another flight due to weather. At 0500, a request for patient transport was received, and the pilot performed a weather check before dispatch. Satellite tracking data showed the helicopter heading east along U.S. Highway 64. About 18 minutes into the flight, the helicopter climbed and turned right away from the course. The last data point indicated a heading of 146 degrees, ground speed 98 knots, and altitude 1,560 feet msl (about 1,116 feet agl). After the pilot did not make a required 10-minute position report, two company aircraft were dispatched. One pilot observed a fire in a rural area about 19 miles west of 60TN. First responders confirmed the crash site.
Personnel Information
The pilot, 47, held a commercial pilot certificate with rotorcraft-helicopter, instrument-helicopter, and airplane single-engine land ratings. His total flight experience was 2,441 hours, including 521 hours in the accident make and model, and 2,250 hours in rotorcraft. In the 90 days prior, he flew 33 hours; in the 30 days, 10 hours. He previously flew with the Memphis Police Department, accumulating about 400 hours in the AS 350, and received all night vision goggle training at Hospital Wing. Training records showed he completed initial AS 350 B3 training on October 31, 2012, including 51 hours ground and 12.1 hours flight (5.8 with NVG). Colleagues described him as a good pilot who followed procedures and used risk assessment tools.
Aircraft Information
The accident helicopter, a 2001 Eurocopter AS350 B3, had a three-blade main rotor, two-blade tail rotor, and a Turbomeca Arriel 2B engine rated at 871 shaft horsepower. It was equipped with skid landing gear, NVG-compatible lighting, Aspen Avionics 1000H PFD/MFD, VEMD, autopilot, EGPWS, and Thales/Sextant DECU. It was not equipped for instrument flight. Maintenance was under the manufacturer's inspection program. Last recorded aircraft time was 6,391.1 hours on October 13, 2013; most recent inspection was a 30-hour inspection on October 11, 2013; last annual was July 17, 2013.
Meteorological Information
The closest weather observation was Fayette County Airport (FYE), about 1.5 nm south-southwest of the accident site. At 0556, the observation included a broken ceiling at 1,600 feet agl, wind 030° at 4 knots, visibility 10+ miles, temperature 11°C, dew point -1°C, altimeter 30.05 inHg. At 0607, conditions were calm wind, few clouds at 800 feet, broken ceiling at 1,200 feet and 6,000 feet, visibility 10+ miles. At MEM, near the departure point, at 0554, wind from 010° at 7 knots, few clouds at 1,200 feet, scattered at 4,700 feet, overcast at 5,500 feet, visibility 10+ miles. Official sunrise was about 0710; civil twilight about 0644.
Wreckage and Impact Information
The wreckage was in a wooded area surrounded by fields, about 3,300 feet south of U.S. Highway 64 in Somerville. The accident site elevation was about 372 feet. Most of the aircraft structure was burned and consumed by impact and post-crash fire. The energy path was about 100 feet long, oriented on a magnetic heading of about 090°, with a flight path angle of about 50°. All three main rotor blades showed powered impact signatures. The tail boom and vertical stabilizer were consumed by fire. Flight control continuity could not be confirmed due to fire damage. The fuel system was consumed; the operator reported the helicopter departed with 101 gallons of fuel. Engine examination showed evidence of rotation at impact. A partial engine teardown confirmed power delivery during a main rotor strike.
Tests and Research
A flight test was conducted on March 24, 2014, using a similar helicopter (N857HW) to examine HTAWS alerts. The test path was flown nine times at decreasing altitudes. HTAWS generated obstacle and terrain alerts, including for a 140-foot cellular tower at 300 feet agl and a 115-foot water tower between 350 and 400 feet agl. No alerts occurred at the accident helicopter's reported altitudes. A simulation by Garmin using accident flight data showed one terrain alert near the second-to-last radar target when flown at about 700 feet msl. Garmin noted the system issues terrain alerts for straight and level flight below 400 feet agl, and can issue alerts at higher altitudes during descent.
Additional Information
Hospital Wing had a formal risk assessment program. The pilot completed a risk assessment form at the start of his shift, evaluating static and dynamic risks. The total risk value calculated at 1759 the previous evening was 11, including factors such as less than one year EMS experience, deteriorating weather, and night flight. The pilot initialed the form and added handwritten notes about precipitation and temperature/dew point spread, though the timing of those notes is unknown.