History of Flight
On February 5, 2014, at approximately 1430 mountain standard time, a Bell 206B helicopter, registration N3211N, was substantially damaged when it rolled onto its right side during the initial phase of an attempted takeoff from a remote landing zone near Bountiful, Utah. Neither the flight instructor nor the pilot under instruction was injured. The instructional flight was conducted under Title 14 Code of Federal Regulations Part 91. The helicopter was operated by the Salt Lake City Utah division of Upper Limit Aviation, a Part 141 certificated training facility. Visual meteorological conditions prevailed, and no flight plan was filed.
According to both pilots, part of the flight was used to practice operations from a snow-covered landing zone in mountainous terrain at an elevation several thousand feet above the school's base airport. The pilots had completed one landing and takeoff at the site. After an uneventful second landing, the helicopter sat on the snow for a few minutes before initiating the next takeoff. Winds were light, and the nose was pointed into the wind. Just after engine power application, the right forward skid sank into the snow, and the pilots were unable to prevent the rollover.
Flight Instructor
The flight instructor held commercial pilot and flight instructor certificates with ratings for airplane single engine, helicopter, instrument helicopter, and helicopter instructor. He had about 1,550 total hours of flight experience, including about 750 hours in the accident helicopter make and model. His most recent flight review was completed in January 2014.
According to the operator's chief safety officer, the operator's policy required that to conduct instruction on snow more than 6 inches deep, the helicopter must be appropriately equipped and the instructor must have received specific training from the chief flight instructor. The instructor had not received that training.
Pilot Under Instruction
The pilot under instruction held a private pilot certificate with ratings for helicopter and instrument helicopter. He had about 244 total hours of flight experience, including about 72 hours in the accident helicopter make and model. He was enrolled in the operator's commercial helicopter certificate course, and the accident flight supported that coursework.
Aircraft Information
FAA information indicated the helicopter was manufactured in 1984 and equipped with a Rolls-Royce (Allison) 250-C20 series turboshaft engine. It was equipped with "tundra pads" mounted near the rear landing skid crosstube. According to the operator, tundra pads are smaller than "bear paws" intended for deep snow but were suitable for snow depths less than about 6 inches.
Wreckage and Impact Information
Neither NTSB nor FAA personnel traveled to the accident site. According to the operator, the helicopter came to rest on its right side on top of the snow. The two-blade main rotor assembly had separated, and both blades were extensively damaged. The right landing skid tube forward of the forward crosstube was bent about 45 degrees up and inboard. Operator personnel stated that damage to the main rotor blades and tail boom was consistent with one or both blades striking the tail boom during the rollover.
Examination of site photographs showed the landing zone area within about a 100-foot diameter was snow-covered and essentially level, but snow depth was not uniform due to variations in underlying terrain. About 15 feet forward and to the right of the helicopter, snow depth was less than 6 inches and grass protruded. Snow beneath and to the right of the helicopter was about 2 feet deep. Company personnel found that the helicopter had landed on snow consisting of a soft layer about 5 to 6 inches thick over a crust of firmer snow on top of a base of about 12 to 18 inches of more soft snow.
The helicopter was recovered the next day and examined by FAA inspectors. Neither the pilots nor the inspectors reported any indications of pre-existing mechanical deficiencies or failures.
Additional Information
The FAA Rotorcraft Flying Handbook describes dynamic rollover: a helicopter is susceptible to lateral rolling tendency when lifting off, caused by factors such as gear stuck in ice, soft asphalt, or mud. Once started, dynamic rollover cannot be stopped by opposite cyclic control alone. For helicopters with counter-clockwise rotor rotation, right-side skid/wheel down is critical because translating tendency adds to rollover force.