Five Marines were killed after an aircraft based at Marine Corps Air Station Camp Pendleton crashed Wednesday near Glamis in Imperial County, California, a Marine Corps official said.

The crash happened around 12:25 p.m., First Lt. Duane Kampa said. The aircraft was a MV-22B Osprey with Marine Aircraft Group 39 and belongs to the 3rd Marine Aircraft Wing, KTLA sister station KSWB reported.

“We mourn the loss of our Marines in this tragic mishap. Our hearts go out to their families and friends as they cope with this tragedy,” said Maj. Gen. Bradford J. Gering, commanding general of 3rd MAW.

The aviation mishap happened during a training mission in Glamis, east of San Diego County. The cause of the crash is still under investigation and crews have also begun equipment recovery operations, 1st Lt. Kampa said.

The identities of the five service members killed have not yet been released, pending notification of next of kin.

Nexstar’s KSWB spoke with military aviation expert and crash investigator Richard Martindell, who says Ospreys do seem to have higher crash rates.

“Looking at the Air Force statistics for the Osprey, they’re running about a 6.0 per hundred thousand hours accident rate, which is high. Most transport aircraft run around under 2.0, so that’s three times the transport aircraft number,” Martindell said.

Martindell, a retired U.S. Air Force fighter pilot, says the sand dunes in Glamis stir up dust that “causes problems for the pilot on landing and on takeoff.” 

“If they’re saying near Glamis, that means they’re not near the airport. It’s out — there’s a training area out in the area of Glamis where they train a lot. What they were doing out there, whether they were in transit or if they were trying to make a pick up or delivery, what they call an in-fill or ex-fill, then that could be part of it too,” Martindell said.