GIBSON, La. -- National Transportation Safety Board investigators were expected to examine wreckage from a southern Louisiana marsh today to help determine why a helicopter bound for an offshore oil platform crashed, killing a North Texas man and seven other people.

The helicopter, operated by PHI Inc., crashed Sunday afternoon shortly after taking off, said Richard Rovinelli, a company spokesman.

Pilots Vyarl W. Martin of Hurst, Texas and Thomas E. Ballenger of Eufaula, Ala. were killed along with six passengers when the helicopter went down in rural Terrebonne Parish, about 100 miles southwest of New Orleans.

The passengers worked for two Shell Oil Co. contractors and the company said they were on their way to its Gulf of Mexico platform.

PHI identified the dead passengers as Allen Boudreaux, of Ama, La.; Andrew Moricio and Ezequiel Cantu of Morgan City, La.; Randy Tarpley of Jonesville, La.; Jorey A. Rivero, of Bridge City, La.; and Charles W. Nelson of Pensacola, Fla.

One passenger, Steven Yeltin of Floresville, Texas, survived and is a patient at Ochsner Medical Center, hospital spokeswoman Katherine Voss said.

Ted Lopatkiewicz, spokesman for the National Transportation Safety Board, said the helicopter is believed to have crashed about seven minutes after it took off at 3:02 p.m. EDT. Lopatkiewicz said there were scattered clouds and visibility was 10 miles at the time of the crash, and the crew reported no problems before the helicopter went down.

A short time after the crash, the Air Force Rescue Coordination Center in Panama City, Fla., received an electronic distress signal from the helicopter with the aircraft's tail number and GPS coordinates, center spokesman Master Sgt. Jeffery Harlan said. The center contacted PHI, which confirmed it couldn't locate the chopper, Harlan said.

The helicopter, a Sikorsky S-76C, would have had a voice recorder aboard and possibly a flight data recorder, Lopatkiewicz said.

At least one recorder was found Monday, said Maj. Tommy Odom, head of the Terrebonne Parish Sheriff's Office water patrol. He didn't have details on exactly what was found. A company spokesman said late Monday he did not know whether the helicopter had a flight data recorder.

Odom said the wreckage was strewn over a fairly small area accessible only by boat, and much of it was visible in chest-deep water. About 20 people helped search, and crews from PHI collected wreckage, he said.

An NTSB investigator also was headed for PHI's offices to go through maintenance and crew records.

Lafayette-based PHI is a primary provider of helicopter services to oil and gas platforms that dot the coast of Louisiana. It also flies medical helicopters.

Workers typically are flown to and from their worksites from coastal flight bases.

Young said the Coast Guard assisted Terrebonne Parish sheriff's deputies in recovering the dead and rescuing the survivor from the marshy Bayou Penchant area, where the offshore oil business blossomed after World War II.

Fishermen and coverall-clad oilfield workers near the crash site speculated the terrain, known for its bounty of catfish and crawfish, would be difficult to investigate.

"It's nothing but marshland out there," said Bobby Breaux, owner of Bob's Bayou Black Marina. "You get out there and try to walk and you'll sink up to your neck."

"No solid land down there," agreed Irving Arceneaux, 72, who had been fishing with relatives in the area.

In June, a PHI Air Medical helicopter crashed in Texas, killing four people. The accident in the Sam Houston National Forest killed the pilot, paramedic, nurse and a patient who was being transported from Huntsville to Houston.

That crew agreed to transport the patient after another helicopter company abandoned the mission, saying cloud cover was too low, making visibility poor in the early morning darkness.