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Navy Chopper, Coast Guard Plane Collide

Last Updated 1:42 p.m. ET

Investigators are trying to determine why a Coast Guard airplane on a nighttime search for a boater collided with one of four Marine Corps helicopters flying in formation to a military training island off Southern California Thursday evening.

All seven people aboard the Coast Guard C-130 plane and the two-person crew of the Marine Corps AH-1W Super Cobra helicopter remain missing Friday.

Search crews this morning were scanning an ocean debris field spotted between San Clemente Island and the San Diego County coast, spokespersons for the Coast Guard and the Marine Corps.

"We are always hopeful ... the assumption is always that they are alive," said USCG Capt. Thomas Farris.

CBS Affiliate KFMB reports the maritime agency sent three cutters and an MH-60 Jayhawk helicopter to the area to search for survivors, while the Navy sent four vessels and multiple helicopters.

"The search conditions are ideal," Lt. Josh Nelson of the Coast Guard told XETV in San Diego. "We've got a clear sky, the winds are calm, the seas are calm, and we have a lot of assets out there."

Pentagon spokesman Bryan Whitman says that although the search continues, the collision likely killed the nine crew members.

The crash was reported at 7:10 p.m., about 50 miles off the San Diego County coast and 15 miles east of San Clemente Island, Coast Guard spokeswoman Petty Officer Allyson Conroy said.

A pilot reported seeing a fireball near where the aircraft collided, Federal Aviation Administration spokesman Ian Gregor said.

Four Marine aircraft - two AH-1W Cobras and two Ch-53 - were conducting an exercise in the area when one of the Cobras collided with a Coast Guard C-130 searching for a missing ship. The other three pilots all witnessed the collision and were able to provide search-and-rescue with very precise locations of wreckage and a tight search area, CBS News national security correspondent David Martin reports, citing a military official.

The FAA's Gregor says the Thursday night crash occurred minutes after FAA controllers instructed the Coast Guard C-130 pilot to begin communicating with military air controllers.

Cpl. Michael Stevens, a spokesman for the Miramar Marine Corps Air Station, confirmed an AH-1W Super Cobra helicopter had gone down, but he had no further information. He said it belonged to the 3rd Marine Aircraft Wing stationed at Camp Pendleton.

The Coast Guard informed the FAA that debris from a C-130 had been spotted, Gregor said.

The C-130 is a long-range surveillance and transport, fixed-wing aircraft that is used to perform a variety of missions.

San Clemente Island is the southernmost of the eight Channel Islands located 68 nautical miles west of San Diego. The Navy has owned and trained at San Clemente Island since 1934, according to the island's Web site. Naval Air Station, North Island is responsible for the island's administration.

Earlier this week, it was an AH-1 Cobra attack helicopter that collided with a UH-1 helicopter over southern Afghanistan, killing four American troops and wounding two more, a Marine spokesman said.

Also this week, a U.S. military helicopter crashed Monday while returning from the scene of a firefight with suspected Taliban drug traffickers in western Afghanistan, killing 10 Americans including three DEA agents in a not-so-noticed war within a war.

U.S. military officials insisted neither crash was believed a result of hostile fire, although the Taliban claimed they shot down a U.S. helicopter in the western province of Badghis.