The air tanker went down Sunday afternoon in the Hamblin Valley area of western Utah, Bureau of Land Management officials said. A helicopter crew saw the crash and told ground crews that "it didn't look good," Iron County sheriff's Detective Sgt. Jody Edwards in Utah told The Salt Lake Tribune.
The two pilots were fighting the fire, which was sparked Friday by lightning in eastern Nevada. It has spread into Utah, though most of the blaze remained in Nevada, about 150 miles northeast of Las Vegas.
Ground and air crews held the fire back from the wreckage, giving sheriff's deputies enough time to drive and hike to the site and confirm that the pilots had died, Edwards said. The fire later overwhelmed the crash site, Edwards said. A medical examiner was helping authorities recover the bodies Sunday night.
The weather was windy and hot, creating "explosive fire conditions," said Tom Harbour, the fire and aviation operations director for the U.S. Forest Service. The terrain was rolling hills with pine, juniper and cheat grass, a thin wispy grass that carries fire quickly.
There was no immediate word on what caused the crash.
The plane was a public-use aircraft, meaning it was contracted with a government agency, and therefore was not subject to Federal Aviation Authority regulations, said FAA spokesman Mike Fergus.
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, Fergus said.
The FAA will conduct its own probe in addition to the lead investigation headed by the National Transportation Safety Board. 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.
The sheriff's office identified the pilots as Todd Neal Tompkins and Ronnie Edwin Chambless, both of Boise, Idaho. They were flying a P-2V air tanker owned by Neptune Aviation Services of Missoula, Mont.
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.
A second air tanker, also a P-2V, malfunctioned Sunday afternoon and was unable to lower all of its landing gear. That crew was helping at a wildfire near the Minden-Tahoe Airport, which is about 50 miles south of Reno. That plane was not owned by Neptune.
That plane remained in the air for another 90 minutes to burn off fuel before making an emergency landing on a runway, Douglas County sheriff's spokesman Jim Halsey said. The aircraft sustained significant damage after it slid off the runway, but both crew members escaped injury, he said.
The incidents come several months after a group of Western senators questioned whether the U.S. Forest Service was moving quickly enough to build up and replace the fleet of aging planes that drop fire retardant on wildfires.
The federal agency hires a mix of large and small airplanes and helicopters each year to fight wildfires. They are generally privately owned and work under contract.
Retardant dropped from planes is typically used to bolster a line cut by firefighters on the edge of a fire, and water dropped from helicopters is usually used to cool hotspots within a fire.
The current fleet is made up of Lockheed P-2Vs, anti-submarine patrol planes dating to the 1950s that have been modified with jets to supplement the piston engines. More than half are due to retire in 10 years.
The number of large aircraft has steadily dwindled since 2004, when the forest service grounded 33 air tankers after a number of high-profile crashes. In March, senators from Oregon, New Mexico, Alaska and California asked the Government Accountability Office to evaluate whether the service had done a good job of analyzing the types and numbers of aircraft needed, the cheapest way to get them, new technologies and where the planes will be based.