On March 23, 2004, about 1918:34 central standard time, an Era Aviation Sikorsky S-76A++ helicopter, N579EH, crashed into the Gulf of Mexico about 70 nautical miles south-southeast of Scholes International Airport (GLS), Galveston, Texas. The helicopter was transporting eight oil service personnel to the Transocean, Inc., drilling ship Discoverer Spirit, which was en route to a location about 180 miles south-southeast of GLS. The captain, copilot, and eight passengers aboard the helicopter were killed, and the helicopter was destroyed by impact forces. The flight was operating under the provisions of 14 Code of Federal Regulations Part 135 on a visual flight rules flight plan. Night visual meteorological conditions prevailed at the time of the accident. The National Transportation Safety Board determines that the probable cause of this accident was the flight crew's failure to identify and arrest the helicopter's descent for undetermined reasons, which resulted in controlled flight into terrain. The safety issues discussed in this report focus on terrain awareness and warning systems for helicopters, flight control system training, flight-tracking technology for low-flying aircraft in the Gulf of Mexico, and preflight testing and maintenance checks for cockpit voice recorders. Safety recommendations concerning these issues are addressed to the Federal Aviation Administration.