A training exercise for a fire crew at an Air Force base turned into a life-and-death struggle when a tanker plane crashed, killing all six crew members and injuring 10 passengers.

The Air Force said Wednesday it hadn't determined the cause of the crash Tuesday afternoon at Wurtsmith Air Force Base. A board of officers will be appointed to investigate the crash.Wurtsmith, located near Lake Huron, is one of two Michigan bases in the Strategic Air Command. Nineteen B-52 bombers armed with nuclear-tipped cruise missiles and nuclear bombs are based at Wurtsmith.

The KC-135 Stratotanker, a four-engine plane used to refuel other planes, was returning to the base from a mission to K.I. Sawyer Air Force Base in Michigan's Upper Peninsula when it crashed and burned, said Staff Sgt. Donald Lawber, a spokesman at Wurtsmith in the northeastern Lower Peninsula.

The six crew members died at the scene, authorities said. Eight of the 10 injured were treated and released from the 379th Strategic Hospital at the base, Staff Sgt. Albert Fleming said. Two people admitted to the base hospital were in good condition Wednesday.

The base's firefighters had just completed a training exercise when the accident occurred, and they quickly doused the flames, said Air Force Sgt. Gene Babble.

The aircraft was making its landing approach when it crashed into the tarmac, said Airman Kim Dvorak, another base spokesman. The plane's pilot had not radioed a distress call before the crash, she said.

A witness, who was not identified, told The Detroit News one of the plane's wings touched the ground as it was landing before it veered out of control. The plane slammed into the ground, skidded more than a quarter mile and came to rest in a grassy area about 150 yards off the runway.

Dvorak said investigators have ruled out wind shear as the cause of the crash, which occurred in sunny weather with light winds. Pinpointing the cause will be difficult, she said, because the plane was not equipped with a flight recorder like the "black box" carried by commercial airliners.

"Not much of an airplane was left," said state police Sgt. John Pegg at the East Tawas post. "Basically, all that was left was a tail section."