Decatur, TX, USA
N16MV
Bell 206B
During lift off from soft uneven terrain, the rear portion of the helicopter's right main skid came in contact with the ground resulting in a dynamic rollover. The pilot reported that the terrain he departed from was "clumpy and lumpy with ruts of grass approximately 1 to 2 feet in height." As he started to lift the helicopter off the ground, he made a slow ascent rate. When the skids were about 1 foot above the ground, he said, "the helicopter stopped for a split second as if something had caught some portion of the right side of the helicopter and the helicopter began a slight lateral roll to the right." The pilot further reported that he recognized the problem too late as he applied full left cyclic and lowered the collective after the helicopter exceeded the critical angle of bank into the low skid to a point where the situation was unrecoverable, and it rolled 90 degrees to the right. No mechanical deficiencies with the engine or airframe were noted. The Rotorcraft Flying Handbook (FAA-H-8083-21), page11-7, described dynamic rollover as, "the pivoting around a skid or landing gear wheel of a helicopter causing it to reach its critical rollover angle. Beyond this point, main rotor thrust continues the roll and recovery is impossible."
On February 18, 2004, at approximately 1330 central standard time, a Bell 206B single-engine helicopter, N16MV, was destroyed following a loss of control during takeoff. The commercial pilot, sole occupant of the aircraft, sustained minor injuries. The helicopter was registered to Skylane Helicopters LLC, of Decatur, Texas, and operated by the United States Forest Service of Atlanta, Georgia. Visual meteorological conditions prevailed and no flight plan was filed for the 14 Code of Federal Regulations Part 133 aerial fire fighting flight. The local flight was originating at the time of the accident. The pilot reported on the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2), that the terrain he was departing from was "clumpy and lumpy with ruts of grass approximately 1 to 2 feet in height." Based on these conditions, he began to lift the helicopter off the ground at an ascent rate of approximately 1 inch to 2 inches per second, and made sure there was no yaw movement with the pedals, nor ground track movement with the cyclic in any direction. When the skids were about 1-foot above the ground, and the pilot was confident that the right front skid-toe was clear of the cable wires for the bambi bucket, "the helicopter stopped for a split second as if something had caught some portion of the right side of the helicopter and it began a slight lateral roll to the right." The pilot further reported that he recognized the problem too late as he applied full left cyclic and lowered the collective after the helicopter exceeded the critical angle of bank into the low skid. He said, "At that point the situation was unrecoverable, and the helicopter rolled 90-degrees to the right severing all control surfaces." According to the Federal Aviation Administration (FAA) inspector, who responded to the accident site, it appeared that the rear portion of the right skid dug into the soft ground as the pilot attempted to bring the helicopter to a hover. Examination of the helicopter revealed damage to the tail rotor, main rotor system, and the rear portion of the right skid was bent. The pilot reported a total of 1,780 hours, all of which were in rotorcraft-helicopter. Of that, 140 hours were in the Bell 206B III. He also reported that there were no mechanical deficiencies with the helicopter or engine. Weather at Decatur Municipal Airport (LUD), near Decatur, Texas, approximately 4 miles north of the accident site, at 1328, reported clear skies, wind from 170 degrees at 13 knots gusting to 18 knots, visibility 10 statute miles, temperature 17 degrees Celsius, dewpoint 2 degrees Celsius, and barometric pressure of 30.31 inches of Mercury. The Rotorcraft Flying Handbook (FAA-H-8083-21), page 11-7, described dynamic rollover as, "the pivoting around a skid or landing gear wheel of a helicopter causing it to reach its critical rollover angle. Beyond this point, main rotor thrust continues the roll and recovery is impossible."
The pilot's failure to maintain control of the helicopter during liftoff after encountering dynamic rollover. A contributing factor was the rough and uneven terrain.
Source: NTSB Aviation Accident Database
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