NTSB Factual Report

On August 1, 2007, approximately 1635 mountain daylight time, a Bell 206B, N268TD, piloted by an airline transport-certificated pilot, was substantially damaged when it yawed to the left and rolled over to the right and struck the helipad while taking off at Rocky Mountain Metropolitan Airport (BJC), Broomfield, Colorado. Visual meteorological conditions prevailed at the time of the accident. The sightseeing flight was being conducted under the provisions of Title 14 CFR Part 91 without a flight plan. The pilot and two passengers aboard the helicopter received minor injuries. One passenger was not injured. The local flight was originating at the time of the accident.

According to the pilot, this was his sixth sightseeing flight of the day. He had just landed and three passengers disembarked. Three other passengers boarded the helicopter. As the pilot brought the throttle to full rpm and increased torque, the helicopter turned left about 15 degrees. Approximately 3 inches of opposite pedal was used to bring the helicopter back to its original heading. The pilot continued to increase torque and as the skids started to come off the ground, the nose pitched up rapidly and the helicopter rolled to the right. The left skid was about 3 inches off the ground during the yaw. The right skid never left the ground. Full forward and left cyclic had no effect. The pilot then lowered collective and tried to roll off the throttle. The helicopter rolled right until the main rotor blades contacted the ground. A piece of main rotor blade struck a nearby hangar. The pilot reported no control anomalies.

On August 15, 2007, the helicopter was examined by FAA and Bell Helicopter investigators. They reported finding no anomalies.

FAA's "Rotorcraft Flying Handbook" (FAA-H-8083-21) defines "dynamic rollover" as "the tendency of a helicopter to continue rolling when the critical angle is exceeded, if one gear is on the ground, and the helicopter is pivoting around that point." It elaborates: "A helicopter is susceptible to a lateral rolling tendency, called dynamic rollover, when lifting off the surface. For dynamic rollover to occur, some factor has to first cause the helicopter to roll or pivot around a skid...until its critical rollover angle is reached. Then, beyond this point, main rotor thrust continues the roll and recovery is impossible. If the critical rollover angle is exceeded, the helicopter rolls on its side regardless of the cyclic corrections made."

NTSB Probable Cause

The pilot's failure to maintain control of the helicopter, resulting in an inadvertent dynamic rollover.