An air tanker that nose-dived in Northern California killing all three crew members was repaired four years ago for cracks in one wing, a representative of the plane's owner said Tuesday night.

The downed C-130A Hercules, operated under contract with the U.S. Forest Service, had just completed a pass over the blaze Monday when its wings snapped off and the fuselage plunged in Walker, Calif.

George Petterson, the lead National Transportation Safety Board investigator at the crash scene, said he was not aware of the earlier wing problem but that it would be examined.

"I have no idea if that's related to what we've got," he said.

The nation's C-130A tankers, workhorse of the firefighting fleet, were grounded Tuesday in the midst of what could become one of the worst fire seasons in history.

Fires were burning in across nearly a half-million acres of tinder-dry forest and brush in seven Western states. Thousands of people have been forced to flee and more than 60 homes have been destroyed, most of them in Colorado.

A wildfire about 40 miles south of Denver grew by 7,000 acres Tuesday night to 120,000-acres, forcing about 2,000 more people to evacuate their homes.

"This fire is so powerful it dictates the wind. First it sucks it in, and then pushes it out," firefighter Mat Wood said.

The C-130A that crashed Monday was fighting a 15,000-acre Cannon fire north of Yosemite National Park. Investigators were trying to determine if a practice campfire set by Marine trainees started the blaze Saturday.

The plane's operator, Hawkins & Powers Aviation Inc., notified the Federal Aviation Administration in April 1998 that an inspection discovered two 1-inch cracks in the surface or "skin" of one of Lockheed-built plane's wings, according to an FAA document obtained by The Associated Press.

In the Service Difficulty Report, Hawkins & Powers described the cracks as near a rivet hole on the bottom of a wing. The damage was repaired and no subsequent problems were reported, a company employee said Tuesday night.

"All I can tell you is there were some wing repairs done to the aircraft. I don't know the extent of that," said Diane Nuttall, an administrative assistant at Hawkins & Powers in Greybull, Wyo. She did not know when the repair work was done.

Records show the 46-year-old aircraft passed its last major inspection in October.

"Near-simultaneous wing failure — I've never seen it," Petterson said.

FAA representatives did not immediately return calls Tuesday night.

The C-130A tankers are only a fraction of the National Interagency Fire Center's fleet of 43 contract planes. Nancy Lull, a spokeswoman for the fire center in Boise, Idaho, said the five planes will be grounded for at least two days while their safety is evaluated.

"They will be shut down until a preliminary investigation can determine what happened to this particular aircraft is unique or that there is some sort of structural problem with all C-130s," said Ed Waldapfel, a Forest Service information officer at the fire center in Boise, Idaho.

Authorities identified the crash victims as pilot Steven Wass, 42, of Gardnerville, Nev.; co-pilot Craig Labare, 36, of Loomis, Calif.; and crew member Michael Davis, 59, of Bakersfield, Calif.

Hawkins & Powers' only previous accident listed in an NTSB database is a 1999 hard landing of a helicopter during coyote research in Utah. The company owns six C-130s and 22 other aircraft.

C-130s, made in the 1950s and '60s, are among the stalwarts of the world's air cargo fleet and were the primary transport used in Vietnam. They are also among the most important weapons in the government's aerial firefighting arsenal because they can hold 3,000 gallons of retardant.

A few hours before the crash, three firefighters in Southern California were burned when flames leaped over their fire truck parked near Interstate 15. They were expected to be released from the hospital by Wednesday.

"For a few seconds, I thought it was over," firefighter Thomas Lotko, 45, said from his hospital bed where his hands and elbows were swathed in bandages. Only the thin skins of emergency fire blankets saved his two colleagues from burning to death.

The top firefighting priority in the Rocky Mountain region was a 44,320-acre blaze in southwestern Colorado. More than 1,700 homes in the Durango area have been evacuated and at least 10 have been destroyed.