* Truck loses control, smashes head-on into bus
* High school students were on way to visit university
* 10 killed, more than 30 injured in crash north of Sacramento (Recasts with further details on investigation, NTSB comments)
By Sharon Bernstein
SACRAMENTO, Calif., April 11 (Reuters) - The investigation into a fiery crash between a FedEx tractor- trailer and a bus that killed 10 people in northern California, five of them teenage students en route to a college recruitment event, focused Friday on what caused the truck to veer out of control.
A day after the accident, it remained unclear whether the FedEx driver was somehow distracted or lost consciousness, or whether a mechanical failure occurred when his truck swerved across the median of Interstate 5 and slammed head-on into the motor coach full of students from the Los Angeles area.
The California Highway Patrol also raised the possibility that a separate collision on the truck's side of the highway might have been a factor in Thursday evening's fatal crash.
According to early highway patrol accounts of the accident, the truck side-swiped a car after crossing the center divider but before hitting the bus.
A powerful explosion unleashed by the impact was so loud it was heard throughout the nearby community of Orland, about 90 miles (145 km) north of Sacramento, said Glenn County Sheriff Larry Jones.
Among the dead were the two drivers, as well as five high school students and a college recruiter on their way north to visit Humboldt State University in Arcata, California, as part of a program to help disadvantaged college hopefuls.
More than 30 others were injured in the wreck.
"We don't know whether the Fed-Ex driver had fallen asleep, whether he experienced a mechanical failure with his vehicle or whether there was a separate collision on the southbound side that caused him to lose control," said Lieutenant Scott Fredrick, the lead Highway Patrol investigator.
A team of investigators from the National Transportation Safety Board began arriving on Friday morning to gather evidence for that agency's independent review of the accident.
NTSB member Mark Rosekind told a news conference late in the day he expected his team to remain on site for about two weeks and would not speculate on the probable cause of the crash.
He said the NTSB probe would examine human factors as well as "the machine and the environment," including highway design elements, vehicle inspection records and driver training and medical records.
The FedEx truck, which was hauling two semi-trailers, was mostly consumed in the fire that followed the crash, but Rosekind said there were sufficient remains of both drivers for authorities to have collected samples for blood and toxicology analysis.
"So right now, one of the things we're in the process of doing is seeing whether or not those required samples were actually collected," he added.
The fire was so intense that it could be days or weeks before some of the bodies can be identified, and investigators will have to rely on dental records or in some cases DNA testing, he said.
TWO OTHER BUSES ARRIVED SAFELY
The stricken motor coach was one of three buses of students traveling from Southern California to participate in a spring break recruitment program at Humboldt State. The two other buses had arrived safely at the campus before the third bus crashed, Rosekind said.
Nestled near the redwoods about 100 miles (161 km) south of the Oregon border, the university every year invites high school seniors from disadvantaged backgrounds or who may be the first in their families to attend college to tour the campus.
The Los Angeles Unified School District, the largest in Southern California, said some of the 19 students from its high schools who were on the tour rode on the ill-fated bus, but it could not say whether any of them were among the victims.
Apart from the driver, the bus was carrying 44 to 48 students and several chaperones, highway patrol spokeswoman Lacey Heitman said. About 34 people were taken by air and land ambulances to hospitals with a variety of injuries, police said.
"They are traumatized, absolutely," another patrol spokeswoman, Tracy Hoover, said. "Most of them have scratches, cuts, burns, contusions and lacerations."
Among those killed was Humboldt State recruiter Arthur Arzola, 26, who worked for the university out of the Southern California community of Rancho Cucamonga, the Sacramento County coroner said on Friday morning.
The school's website describes Arzola as a counselor and recruiter. In a biography on the site, Arzola characterized himself as hard-working, compassionate and friendly, and described the university as offering "incredible opportunities that change the world for the better."
A recently engaged couple serving as chaperones were also among the dead, local media reported.
Jonathan Gutierrez, 17, told NBC's "Today" show that after the crash the bus filled with smoke and students broke windows to escape. "It was a very surreal moment," he said.
"All of a sudden I heard people screaming," said Gutierrez, who had been asleep before the impact.
Pictures from the scene showed the bus reduced to a burned-out chassis resting sideways across the highway. Yellow tarps were draped over what appeared to be bodies in the wreckage.
"The big rig and the bus were both engulfed in flames. You are talking about two vehicles that are destroyed. There is hardly anything left of the truck," Hoover said.
Bonnie Kourvelas, a spokeswoman for FedEx Corp, said the company was aware that one of its trucks was involved in the crash and is "cooperating fully with authorities."
Humboldt State President Rollin Richmond said the students were to attend a spring preview event on Friday.
"Our hearts go out to those who have been affected, and we are here to support them, and their families, in any way possible," he said in a written statement. (Reporting by Sharon Bernstein in Sacramento, Dana Feldman, Dan Whitcomb and Alex Dobuzinskis in Los Angeles and Eric Johnson in Seattle; Additional reporting by Laila Kearney in San Francisco and Colleen Jenkins from North Carolina; Writing by Steve Gorman; Editing by Cynthia Johnston, Richard Chang, Gunna Dickson and Ken Wills)