Sikorsky S-76A, Santa Maria, Calif., June 27, 2008–The pilot’s misjudgment of clearance from an object during a hovering turn for landing was the probable cause of the crash of an S-76A operated under Part 135 by Arctic Air Service, the NTSB has determined. Contributing to the accident was an inadequately marked heliport surface and the close proximity of an obstruction to the landing area. While approaching to land on an oil platform, the S-76’s copilot made a right pedal turn and struck a movable derrick with the tail rotor, losing tail rotor control. As the copilot immediately landed on the helipad, the left main gear collapsed, rolling the helicopter onto its left side and causing structural damage to the tail and main rotor assemblies. Six days before the accident, the derrick on the platform had been repositioned to its new location seven feet from the edge of the heliport deck. The operator reported that the landing deck on the platform is 50 feet by 50 feet, while the decks on the other oil platforms served by Arctic Air are larger, at approximately 70 feet by 70 feet. The helipad had been stripped and repainted not long before the accident. The H symbol was offset from its previous position, and the reference line had not been restored. According to the copilot, about 99 percent of approaches to land on the platform are made from the southwest, but in this case the wind dictated an approach from the northeast. Of the 10 people on board the helicopter, one suffered minor injuries.