An Airbus AS350B3 operating as an emergency medical services flight crashed near Somerville, Tenn., because the pilot lost control of the aircraft, according to the NTSB's final report on the Oct. 22, 2013 nighttime crash. The pilot and two medical crew on board perished in the crash.
The Saftey Board believes the accident was precipitated by the pilot’s inadvertent encounter with instrument meteorological conditions at the same moment he was apparently attempting to respond to an obstacle alert generated by the helicopter’s terrain avoidance warning system (HTaws). The helicopter was equipped with night-vision goggles (NVG) and NVG-capable lighting, and the pilot had been trained on the use of NVG. The helicopter was not equipped for flight under IMC.
The helicopter departed Memphis Hospital Wing heliport at approximately 5:47 p.m. into night visual metoerological conditions with the pilot and two medical staff on board en route to pick up a patient in Bolivar, Tenn. Satellite tracking data revealed the helicopter proceeded east for approximately 18 minutes following a U.S. highway. At that point, the tracking system recorded the helicopter entering a climbing right turn at approximately 1,100 feet agl until the data ended at 6:05 p.m. The wreckage, largely consumed by a post-crash fire, was later found in a wooded area about 3,300 feet south of the highway. No eyewitnesses could be located.
The investigation determined that the helicopter impacted trees at a steep angle and that the orientation of the main wreckage indicated a loss of control. Examination of the airframe, rotor system and engine did not reveal evidence of a preexisting mechanical malfunction. Rotational signatures on the main rotor and engine indicated that the engine was producing power at the time of the accident.
A review of weather conditions around the time of the accident revealed a few clouds at 800 feet agl and a broken ceiling existed at 1,200 feet agl within two miles of the accident site.
The investigation also identified two obstacles in the immediate vicinity. One (an unlit, nonoperational cellular tower) stood 140 feet tall, while the other (a water tower) was 115 feet high. Although the helicopter’s HTaws did not record data, post-accident research indicated a possible obstacle alert that might have prompted the pilot to climb and enter the IMC conditions in which he lost control of the helicopter.