Gilbert, IA, USA
N1396X
BELL 47G 4A
The commercial pilot was conducting an aerial application flight. The pilot reported that, while about 150 ft above ground level, he rapidly pitched the nose up to avoid an obstacle and then pitched it nose down to a steep descent angle. When the helicopter entered the nose-low attitude, the engine experienced a total loss of power. The pilot subsequently made a forced landing to a corn field. The pilot reported that he thought the loss of engine power might have been due to the nose-low attitude, which allowed the fuel to shift in the tanks and starve the engine of fuel. He also reported that he never flew the helicopter with less than one quarter of the fuel tanks full (about 15.25 gallons). The helicopter's type certificate holder also noted that, if the helicopter was low on fuel and then put into an abrupt nose-low attitude, the engine could be starved of fuel. During the postaccident examination, 11 to 12 gallons of fuel were drained from the tanks. An engine test run was conducted with no abnormalities noted. Based on the evidence, it is likely that the engine was starved of available fuel due to the rapid and steep descent, which shifted the fuel in the tanks.
On July 24, 2015, about 1800 central daylight time, a Bell 47G 4A helicopter, N1396X, made a forced landing after a loss of engine power near Gilbert, Iowa. The commercial rated pilot and sole occupant was not injured. The helicopter sustained substantial damage. The helicopter was registered to and operated by Fly Right Heli LLC, Adel, Iowa, under the provisions of 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed. The pilot reported he was returning to his truck to refill the helicopter with more application. While flying about 150 ft above ground level, he maneuvered the helicopter upward to avoid an obstacle. During the maneuver he rapidly pitched the nose up to climb and then pitched the nose down to a steep angle of descent. When the helicopter entered the nose low attitude, the engine experienced a total loss of power. The pilot made a forced landing to a corn field. The pilot reported no mechanical malfunctions with the helicopter. The pilot speculated the loss of engine power was attributed to the nose low attitude which allowed the fuel to shift in the tanks and starve the engine of fuel. He also reported that he never flew the helicopter with less than one quarter of the fuel tanks full (about 15.25 gallons). The responding Federal Aviation Administration (FAA) inspectors conducted a postaccident examination of the helicopter and an engine test run. The helicopter's rotor blades, fuselage and tailboom sustained impact related damage. Due to the impact damage, a flight control check could not be accomplished. During the test run, the engine operated normally and no anomalies were noted. The inspectors recovered 11 to 12 gallons of aviation gasoline from the fuel tanks. The helicopter's flight manual indicated that the helicopter is capable of carrying 61 total gallons of fuel, 57.5 useable gallons. A review of the maintenance records revealed that an annual inspection was completed on July 1, 2015. The same logbook entry indicated that an engine overhaul and 1,200 hour inspection were completed on the transmission and main rotor mast. A review of the helicopter's flight manual yielded no limitation on minimum fuel or limitations of maneuvers due to low fuel quantity. The helicopter's Type Certificate owner stated that if the helicopter was low on fuel and then put into an abrupt nose low attitude, it's possible that the engine was starved of fuel.
The total loss of engine power due to fuel starvation because the available fuel shifted within the tanks due to an abrupt nose-low maneuver to avoid an obstacle, which resulted in a hard forced landing.
Source: NTSB Aviation Accident Database
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