Once a Cold War-era submarine attack plane, the Lockheed P-2V has for years been both a mainstay of the nation's aerial firefighting arsenal and a cause for concern.

Flying in the turbulent, unforgiving skies above raging wildfires, the planes have crashed at least seven times from either mechanical problems or pilot error, causing 16 deaths, dating back to 1990 when they were slowly added to the nation's firefighting fleet.

The latest crash in Utah that killed two pilots and a crash-landing by another one of the same planes in Nevada, both on Sunday, have renewed calls for the federal government to speed up efforts to modernize aircraft used to drop fire retardant.

All of it, just as the busiest part of the wildfire season begins in the West.

"As the air tanker fleet continues to atrophy, it's going to reduce the country's ability to get there early, which is why so many of these fires mushroom," Sen. Ron Wyden, D-Ore., chairman of the Forestry Subcommittee, said Monday.

Wyden led a push in March by a group of senators from the West to get the U.S. Forest Service to bring newer planes into service.

On Sunday, a tanker went down in western Utah as crews battled a lightning-sparked wildfire that jumped the Nevada border about 150 miles northeast of Las Vegas.

Iron County Sheriff Mark Gower said Monday it appeared a wing tip hit the ground in a rocky canyon. The plane practically disintegrated, leaving a 600-yard debris field, he said.

Authorities said ground crews tried to keep the fire from overwhelming the wreckage to give officials enough time to confirm the pilots had died, but flames soon swept through. The men's bodies were eventually recovered later in the day.

By Monday, the fire had grown to 8,000 acres with 15 percent containment, authorities said. Crews didn't expect full containment until Sunday.

The weekend weather was windy and hot, creating "explosive fire conditions," said Tom Harbour, the U.S. Forest Service's fire and aviation operations director. The terrain is rolling hills with pine, juniper and cheat grass, a thin wispy weed that carries fire quickly.

The plane, owned by Neptune Aviation Services of Missoula, Mont., was built in 1962, according to federal aviation records, but had been modified to fight fires and was among only a handful of air tankers available nationwide.

Another P-2V, this one owned by Minden Air Corp. in Minden, Nev., was fighting a wildfire south of Reno on Sunday. Its crash-landing at Minden-Tahoe Airport was captured on video, with the plane dropping to its belly and sliding across the runway. No one was injured.

The government previously had relied primarily on C-130 cargo planes for firefighting efforts but started slowly adding P-2Vs to the fleet in the early 1990s, then began relying much more on the planes after two C-130 crashes in 2002.

The number of large firefighting aircraft has steadily dwindled since 2004, when the Forest Service grounded 33 air tankers after a number of high-profile crashes. Two of those involved the wings falling off the aircraft as they were fighting fires.

That left 11 tankers at the start of this year to mount aerial assaults on wildfires. Among those were nine P-2Vs like the one that crashed over the weekend in Utah. A DC-10 and a BAE-146 make up the rest of the fleet.

"They are aging, and we know we need to replace them," Harbour said. "That's why the chief (of the Forest Service) sent Congress an air tanker strategy a couple months ago that said we needed to modernize the fleet."

Harbour said the agency has concluded that the nation needs 18 to 28 of the next generation of air tankers, those that can fly faster and carry more retardant. Overall, the Forest Service budgets $70 million a year on firefighting aircraft out of $2 billion overall fighting wildfires. Bids are being evaluated on the next generation planes, but the service currently pays $10,000 a day and $6,000 per hour of flight time for exclusive-use contracts.

A review of firefighting plane crashes over the last two decades found that the P-2V aircraft had been involved in at least seven crashes while fighting wildfires, including the one that crashed on Sunday.

Neptune Aviation, which owns five of those planes, reported several hydraulics failures on their P-2Vs, one that led to an emergency landing in Montana in April. Another one was taken out of service in February after workers found a crack in the wing support.

Neptune released a statement Monday afternoon that said it would not comment on accident specifics, but noted the aircraft "made contact with the ground while flying in the active fire drop zone."

The company temporarily grounded its fleet so its flight operation and maintenance directors could debrief crewmembers and mechanics. All of the company's air tankers have been returned to active duty, the statement said.

The National Transportation Safety Board planned a news conference for Monday evening in southern Utah to discuss the deadly crash. Meanwhile, authorities continued to investigate the cause.

While the plane was under contract to the government and not subject to Federal Aviation Administration regulations, the agency said it, too, would conduct a probe.

The investigation will look at whether there was a mechanical issue with the plane, whether there was pilot error or whether weather contributed to the crash.

There were no air traffic control services and the pilot was flying under visual flight rules at the time of the crash 50 miles west of Cedar City, said FAA spokesman Mike Fergus.

The sheriff's office identified the pilots as Todd Neal Tompkins and Ronnie Edwin Chambless, both of Boise, Idaho.

Tompkins' wife Cassandra Cannon said her husband had flown air tankers for 17 years and believed the work he did was meaningful and impacted the safety of others. She said Tompkins was dispatched to the wildfire Sunday and immediately began flyovers.

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Associated Press writer Matt Volz in Helena, Mont., Jeff Barnard in Grants Pass, Ore., and Todd Dvorak in Boise, Idaho, contributed to this report. Sonner reported from Reno, Nev., and Skoloff from Salt Lake City.