LAX00GA286

The loss of control in hovering flight and impact with terrain for undetermined reasons.

During takeoff, prior to transitioning to forward flight, the helicopter rolled violently to the right one complete revolution, impacting the ground inverted and then coming to rest upright on its skids. A passenger in the left, front seat, restrained by a lap belt and partially restrained by a shoulder belt that separated under load, was struck on the helmet and left shoulder by a main rotor blade that swept along the left side of the helicopter and was seriously injured. A passenger in the left rear seat, with a lap belt but without a shoulder restraint available, was partially ejected from the helicopter and was struck by the passing main rotor blade and fatally injured. Six witnesses and the pilot reported the helicopter was hovering at between 2 and 5 feet above the ground before the roll ensued. In the 2-hour period before the accident, a thunderstorm passed west of the accident location and there was a windstorm at the accident location estimated to have been 50 - 60 knots. The main and tail rotor blades were secured during the windstorm. At the time of the accident, the wind was steady on the nose of the helicopter at 5 - 10 knots. None of the witnesses reported observing any dust devils or unsteady wind. The ground surface near the initial hover location, where marks may have been present, was obscured by emergency vehicle movement and rain that fell after the accident and prior to the investigator's arrival on-scene. The investigation and laboratory examination of fracture surfaces did not reveal any evidence of preaccident mechanical failures.

HISTORY OF FLIGHT On August 3, 2000, at 1855 hours Pacific daylight time, a Bell 206L-1, N10864, was destroyed when the helicopter abruptly rolled to the right and impacted terrain during hover after takeoff at Montello, Nevada. The helicopter was operated under 14 CFR Part 91 in support of firefighting activities as a public-use aircraft by the United States Bureau of Land Management. One passenger was fatally injured and the other passenger was seriously injured. The commercial certificated pilot was not injured. Visual meteorological prevailed and no flight plan was filed for the positioning flight that was destined for Wells, Nevada. There were six ground-based crewmembers affiliated with the operation of the helicopter that witnessed the accident. All of the witnesses were together as a group about 50 feet south of the departing helicopter and viewed the helicopter from the left-side perspective. The witnesses provided a consistent opinion that the helicopter was clear of the ground, in a stable hover at 2 to 5 feet above the ground, when it suddenly rolled to the right and crashed. Two witnesses described the rolling maneuver as "hard" and "violent." There was some disagreement about whether the helicopter rolled to the right until inverted and then bounced back to the left back up on its skids, versus rolling to the right one complete revolution to end up upright. Some commented that the flying dirt and debris from the helicopter was confusing. None of the witnesses described the maneuver as a yawing or spinning maneuver, but rather as a roll about the longitudinal axis. According to two of the witnesses, the witness statements (attached on Elko County Sheriff's forms) were prepared the morning following the accident. One witness said that no one talked much during the bus trip back to Elko or during dinner on the evening of the accident. After dinner this witness went to her room; however, several of the others went to the bar. She did not recall discussing the circumstances surrounding the accident prior to preparing her statement. The second witness said that in the interim between the time of the accident and the time the written statements were prepared, there were "some" but "not a great deal" of discussion among the witnesses regarding there perceived observations. The helicopter crew supervisor was interviewed August 5, 2000. He reported that, on the day of the accident, he was supervising a crew of about 10 people assigned to place radio repeater equipment in proximity of a fire near Montello. The crew originated in Wells in the morning. The pilot and two crewmen, who were later in the day to be the three persons aboard the helicopter during the accident, flew the helicopter to the helicopter attack (helitack) base at Montello. He and the other support personnel drove to the base. After arrival at the base, two flights were flown during the day to place radio repeaters. About 1600, a high-wind warning was issued and the wind started to blow. The pilot tied down the rotors of the helicopter using a cap that fit over the rotor tips and tied to the entry steps of the helicopter in front and to the landing gear skid on the right side in back. The wind blew hard for about 2 hours, reaching about 45 mph, and subsided about 1800. About 1830, the wind had dropped to 10-12 knots, and the pilot thought it would be safe to return to Wells. The pilot removed the rotor tie downs and was observed putting them aboard the helicopter and preflighting the helicopter as his two passengers were putting their equipment aboard. When they boarded the helicopter, the pilot was in the right front seat, one passenger was in the left front seat, and the second passenger was in the left rear seat. The helicopter was headed west and the winds were steady from the west at 10 - 15 knots. The crew supervisor said he thought the engine start and pretakeoff checks seemed normal, and he recalled the pilot advised via the radio they were leaving. The helicopter lifted to a 2- or 3-foot hover and the supervisor looked away. He then heard a noise that he thinks may have been the rotors striking the ground, and, when he looked back, the helicopter was rolling quickly to the right. He recalled seeing one rotor blade strike the left side of the fuselage at shoulder height of the left front passenger and down the left side of the helicopter. The engine sound level seemed to increase. He yelled for his people to call [on the radio] for help and when he looked back at the helicopter it was back upright on its skids, 30 feet north of where it had been, and still headed west. He ran, with others, to the helicopter. The engine was still running but was spooling down as they reached it. The pilot emerged from the aircraft with a look of confusion and disbelief on his face. The left front passenger was unconscious for 5 - 10 minutes and then regained consciousness but was incoherent. The passenger in the left rear seat was unconscious and did not respond to CPR. The supervisor said he did not recall any side-to-side, fishtailing motion and, during an interview with the Safety Board investigator, used his hand to describe a rolling maneuver. He was certain that the helicopter was hovering clear of the ground and the wind was steady at 10 - 12 knots. Within 1 hour the wind was calm. He said that, after the accident, the rotor blade tie down straps were still on the shelf in the cabin. In his interview, also on August 5, 2000, the pilot said that on the day of the accident he had flown three flights; one ferry flight to Montello, and two communications missions to place repeaters. There were no discrepancies on the aircraft. The only abnormality he noted was an unexplained "thump" sound heard by him and one other crewmember during the second communication flight. He heard the "thump" and thought that he felt it in the airframe. The winds were gusty and he thought it might have been due to turbulence. After the flight, since there was no mechanic on site, he looked at the rotor head himself but saw nothing unusual. Between 1500 and 1830, there was a windstorm with wind gusts of 50 - 60 knots associated with a thunderstorm that passed west of their location. The pilot tied down the main and tail rotor blades before the windstorm, and by 1845, the weather was clear enough to return to Wells and the wind had decreased to 5 - 10 knots. The pilot preflighted the helicopter, untied the rotors, and hooked up the battery that he had disconnected to prevent inadvertent discharge at the remote location. He said that, after boarding the passengers, the start and pretakeoff checks were normal. He performed a normal hydraulics-off control check. He "picked the helicopter up" to a 3-foot hover height and glanced down at the engine torque gauge that he recalled was at 80 percent torque. Suddenly, the helicopter did a "violent snap roll" to the right coming to rest upright. He estimated the whole event only lasted about 1/4 second. The first thing he recalled was dirt hitting the helicopter and he could not be certain if the helicopter rolled all the way over or not. He was certain he had not yet started his transition to forward flight. The pilot added that the wind was on the nose of the helicopter at less than 10 knots, there was no yaw associated with the event, it was pure roll, and the engine operated "fine" the entire time. The engine was still running after the accident and he had to shut it off manually. There was no change in audible tone prior to the roll, although he may have heard another "thump" sound similar to the one heard on the earlier flight. He did not recall any movement or abnormal feedback in the antitorque pedals or the cyclic and collective controls prior to the accident. When the Safety Board investigator inquired about the 1/4-second duration of the event and how brief a time period