Several teams of NTSB investigators, comprising eight officials, are working with the Highway Patrol and the Utah Department of Transportation to determine the cause of the accident.

Preliminary results should be available by next week, said Peter Kotowski, the NTSB investigator in charge.

Officials have recovered the black-box data recorder that may help them determine the cause of the crash.

NTSB investigators have talked with the driver, Welland Lotan, 71, of Apache Junction, Ariz. But Kotowski said he could not yet make available the content of that interview.

The investigation will take into account the driver's experience, the roadway conditions and the condition of the bus. The badly damaged vehicle is now in Green River, according to UHP Sgt. Rick Eldredge.

A sign warned of an upcoming curve, Kotowski said. Passengers on the bus have said it fishtailed, slapped against a guard rail, slid down an embankment and rolled at least once.

The top of the bus was sheered off.

Fifty passengers were thrown from the bus. The driver was one of only three people to remain on board.

The bus was one of 17 from Arrow Stage Lines that left Phoenix on Jan. 3 for the ski area at Telluride, Colo. The buses were returning three days later when the accident occurred.

A second bus came upon the accident scene about 30 minutes after the rollover, Kotowski said.

csmart@sltrib.com