Authorities on Monday were trying to discern how two helicopters battling a small fire in Riverside County collided, leaving three people dead.

The two choppers struck each other around 7:05 p.m. Sunday near Cabazon, with one crashing and the other landing safely. The incident marks a rare instance in which the aviation battle of a California wildfire resulted in a mid-air crash.

“This was a tragic loss,” said David Fulcher, the California Department of Forestry and Fire Protection’s southern region chief.

The three people killed in the crash were identified as a Cal Fire division chief, a Cal Fire captain and the contract pilot of the helicopter.

Cal Fire identified two of the victims in an internal email as Assistant Chief Josh Bischof and Fire Capt. Tim Rodriguez. The third victim was identified only as an “exclusive use helicopter pilot.” Friends from Cal Fire confirmed the deaths online.

Cal Fire Assistant Chief Josh Bischof, shown at the unveiling of a S70i Cal Fire Hawk helicopter at Hemet Ryan Air Attack Base, was among those killed in Sunday night’s collision.

(California Department of Forestry and Fire Protection Facebook page)

Bischof was promoted to assistant fire chief in March, according to a Facebook post from his wife. He was previously the battalion chief at Hemet Ryan Air Attack Base, one of the 14 air attack bases that Cal Fire has across the state. Before that, he worked in Menifee for the Riverside County Fire Department. Rodriguez also worked for Hemet Ryan Air Attack Base and knew Bischof, according to Facebook posts.

Bischof had spent many years directing aerial attacks of fires from aircraft. He routinely posted photos from high above fires burning in Riverside County. He worked on the Camp fire, which ripped through the town of Paradise in 2018, he told outlets.

“This is certainly one of the worst fires in California history,” he told a CBS reporter at the time as they flew over the Paradise destruction. “It’s the most destruction I’ve ever seen.”

The National Transportation Safety Board is investigating, Fulcher said, and investigators were expected to arrive Monday afternoon to document evidence at the scene and examine the aircraft. The investigation also will examine radar data, weather, maintenance records and the pilot’s medical records, spokesperson Jennifer Gabris said.

“At this early stage of an investigation, NTSB does not state a cause but will provide factual information when available,” Gabris said. A preliminary report is likely within 15 days, but the full investigation could take one to two years to complete.

Nick Schuler, deputy director of communications and emergency incident awareness with Cal Fire, said he “couldn’t even begin to speculate what caused [the collision] to occur.”

Fulcher said Cal Fire and the Riverside County Fire Department had been dispatched to a reported structure fire around 6 p.m. Sunday near Broadway Street and Esparanza Avenue in Cabazon.

A full wildland fire response team, including fixed- and rotary-wing aircraft, was dispatched to the scene because the fire — dubbed the Broadway fire — was reported to have spread to vegetation, Fulcher said.

The crash ignited a separate 4-acre blaze, called the Bonita fire, which was extinguished, Fulcher said. He did not elaborate on the type of fuel that caught fire but described it as “the typical grass and vegetation in the Cabazon area.”

Fulcher did not confirm whether any homes were near where the helicopters collided.

Skies were mostly clear Sunday evening, with no visibility restrictions around the time of the crash, the National Weather Service said Monday. Winds were blowing out of the south and southwest about 15 to 20 mph.

The aircraft that crashed was a Bell helicopter that was responsible for observation and coordination, officials said. The second helicopter — a Sikorsky S-64 helicopter, also called a Skycrane — was able to make a safe landing with two people on board. Fulcher said he could not confirm whether the Skycrane, which typically is a water-dropping helicopter, was dumping retardant or water during its flight.

Both helicopters were contracted by Cal Fire on an as-needed basis, Fulcher said.

Twitter user DanielFireCopter, who reports regularly on California wildfires, posted that he saw three helicopters deployed but only one returning to nearby Hemet. He shared a picture of the Sikorsky, prior to the crash, against a blazing red sky.

“What makes it more sad is that I saw both of them heading to the fire … and only seeing Copter 301 returning to Hemet saddens me,” he wrote, adding that not being able to see all three helicopters return “feels haunting.”

Several additional aircraft were assigned to support the blaze. Fulcher said it is “not an uncommon dispatch for a wildland fire to send those resources.”

Officials said the helicopters involved were among 24 exclusive aircraft secured by Gov. Gavin Newsom earlier this year to help bolster Cal Fire’s fleet. The aircraft were contracted for a period of 90 to 120 days.

“These aircraft have been strategically located in communities across California and will be pre-positioned to meet the needs of potential fire activity throughout the state,” the agency said in a July 1 news release about the program, which was funded as part of a $72-million investment from the governor to enhance firefighting response.

Cal Fire has the largest civil aerial firefighting fleet in the world, including more than 60 fixed and rotary-wing aircraft.

Schuler said firefighting flights are standard procedure for the agency, which dropped more than 15 million gallons of water and 9 million gallons of retardant over wildfires in 2022 alone.

“This is something we do every single day, and our pilots are highly proficient,” he said. “Our folks are world-renowned aviators. Obviously, it’s a tragic loss.”

In 2014, a Cal Fire air tanker crashed while battling the Dog Rock fire near Yosemite National Park, killing the pilot. In 2008, a Sikorsky firefighting helicopter operated by the U.S. Forest Service collided with trees and terrain during takeoff near Weaverville, killing nine and seriously injuring four others.

But Schuler said he could not recall any similar incidents involving two aircraft colliding.

“It’s so, so rare that these things occur,” he said.