Col. Carol McBride told reporters Thursday at Camp Pendleton that the crew of the twin-rotor Sea Knight helicopter was flying too low and too fast when it approached a landing pad on a Navy tanker off the coast of San Diego.
The Marine Corps found that the aircraft and weather were not factors in the accident. The pilot and copilot who survived the crash will not be prosecuted but they could face administrative penalties.
McBride also announced that a posthumous medal will be awarded to Gunnery Sgt. James Paige of Middlesex, N.J., who died while trying to save crew members from the downed aircraft.
A videotape of the accident obtained by CBS San Diego affiliate KFMB-TV shows that the helicopter got stuck on a metal safety net and was pulled into the ocean. The pilot then applied full throttle, lifting the chopper sideways into a somersault into the Pacific.
The chopper had just taken off from an amphibious assault ship en route to the USS Pecos, the Navy tanker that provides fuel to ships at sea.
The Marine Corps said part of the group's training involved repelling from the chopper to the ship, and 14 Marines were ready to rappel 30 feet down a rope onto the Pecos.
After the crash, rescue helicopters rushed to the scene and managed to quickly pluck 11 Marines from the water. The 23,000-pound chopper was submerged in 3,600 feet of water.
The military has implemented a number of changes in the wake of the fatal accident, such as increasing the minimum altitude for that type of helicopter exercise.