On June 27, 2008, about 1233 Pacific daylight time (PDT), a Sikorsky S-76A, N343AA, collided with a steel beam on Oil Platform Irene, off the coast of Santa Maria, California. Arctic Air Service, Inc., was operating the helicopter under the provisions of 14 Code of Federal Regulations (CFR) Part 135. The airline transport pilot and eight passengers were not injured; the airline transport pilot certificated copilot received minor injuries. The helicopter sustained substantial damage. The flight departed Santa Maria Public Airport, (SMX), Santa Maria, California, about 1202, with planned stops at Platform Hidalgo, Platform Hermosa, and Platform Irene, before returning to Santa Maria. Visual meteorological conditions prevailed for the flight, and no flight plan had been filed. According to a written report from the operator, the helicopter departed Santa Maria, and made stops at Platform Hidalgo and Platform Hermosa. It departed Platform Hermosa for Platform Irene with eight passengers on board, and was to be shutdown for a period of time while on the platform. In a conversation with a Federal Aviation Administration (FAA) inspector, the copilot stated that he was at the controls for the approach and landing at Platform Irene. He reported that about 99 percent of the time an approach is made to the northeast, but he performed an approach to the southwest that day because of the wind direction. The operator reported that during the landing and a right pedal turn over the heliport at Platform Irene, the tail rotor of the helicopter struck a movable derrick. The copilot lost tail rotor authority and landed immediately. The left main gear collapsed, and the helicopter rolled onto its left side. The helicopter received structural damage to the tail rotor and main rotor assemblies. The operator reported that there were no mechanical malfunctions or failures of the helicopter. They noted that winds were from 220 degrees at 6 knots. They also reported that the movable derrick on the platform had been positioned in the closest possible location to the heliport area. The operator reported that the landing deck on Platform Irene is 50 feet by 50 feet, at an elevation of 110 feet. The decks on the other oil platforms operated on by Arctic Air are larger, about 70 feet by 70 feet. In the section titled RECOMMENDATION (How could this accident have been prevented) of the operator's written report (NTSB Pilot/Operator Report, Form 6120.1), the operator stated that the flight deck on Platform Irene had recently been repainted. The "H" symbol was offset from the previous position, and the reference line had not been repainted. He reported that pilots used the reference line, or "Butt Line," to determine where the pilot seat would have to be located to allow adequate tail rotor clearance when "swinging" the tail around. The operator recommended that the "H" symbol be repositioned, and the reference line be repainted. He also thought that a profile view depiction of the flight deck and surrounding obstacles could be published to help pilots determine possible problems with particular approach paths. Lastly, he recommended that all company pilots be briefed on these changes and the associated hazards and methods to avoid similar accidents in the future. The Arctic Air Service Safety Officer reported that the derrick had been moved to its location adjacent to the southeast edge of the heliport deck 6 days before the day of the accident. She stated that Platform Irene is the only platform Arctic Air operates on with a movable derrick that can be positioned to that location, which is within 7 feet of the heliport deck. The Safety Officer reported that the deck had been stripped and repainted about 2 months before the accident. She stated that the new "H" marking painted on the deck was 23 feet from the southeast edge; the previous location of the "H" was about 1 foot farther from this edge. The markings on the deck of Platform Irene were different than those on all the other decks before being repainted to match the other decks. An FAA representative stated that there are no FAA regulations defining requirements for markings on these offshore heliports.