On May 13, 2011, about 1120 central daylight time, a Bell 206L-4, N266P, landed in the Gulf of Mexico near the Mobile Block 114CC helideck following an in-flight loss of directional control. The helicopter was substantially damaged. The helicopter was registered to and operated by PHI, Inc. under the provisions of 14 Code of Federal Regulations Part 135 as a passenger flight. Visual meteorological conditions prevailed and a company visual flight rules flight plan was filed. The two pilots sustained serious injuries and the passenger was not injured. The flight was originating at the time of the accident. According to the operator, the pilot positioned the helicopter for a west-southwest departure due to prevailing wind conditions. After clearing the edge of the production platform helideck, the helicopter started a slow yaw to the right. The pilot added full left pedal; however, this did not stop the rotation. After 360 degrees of rotation, the rotation quickened, the pilot stated that he "didn't have a tail rotor," and he lowered the collective and rolled the throttle to idle. The pilot deployed the emergency floats, and the helicopter impacted the water slightly nose low and in a right drift. The helicopter rolled over immediately to the right and stayed afloat. The pilot egressed the helicopter through the broken windscreen area, the left seat pilot egressed through the pilot's open door, and the passenger egressed through the left passenger door. The wreckage was recovered to the operator's facilities in Lafayette, Louisiana where an examination of the wreckage was performed on May 18, 2011. An inspector with the Federal Aviation Administration (FAA) provided oversight for the examination, assisted by the operator and an investigator from Bell Helicopter. The examination of the engine, tail rotor gearbox, tail rotor drive shaft, main gear box, and main rotor system did not reveal evidence of a pre-existing mechanical malfunction or anomaly. All long tail rotor drive shaft segments were connected. The tail rotor gear box was manually turned, and drive shaft continuity was verified. There was rotational scoring of the tail boom surface in the area of the tail rotor blades. No unusual noise was noted when the tail rotor gear box was rotated in both directions. The tail rotor pedals moved in both directions and no binding was noted. FAA inspectors conducted an interview with the pilot after the accident. The pilot reported that, immediately prior to the loss of directional control, the winds were coming from the left, front quarter of the helicopter. The FAA inspector reported that this would have put the helicopter in an area of main rotor disc interference with the tail rotor, which could have resulted in a loss of tail rotor effectiveness.