A U.S. Air Force U-2 high-altitude reconnaissance plane crashed shortly after takeoff from Beale Air Force Base in northern California during a training mission Sept. 20, the service said.

The fate of the plane’s two pilots was not immediately clear. The Air Force initially said that they had ejected, but later said that it had no information about their status. A recovery mission was under way at press time, said Gen. Hawk Carlisle, commander of Air Combat Command, who spoke at an Air Force Association conference near Washington, D.C.

An Air Force U-2 flies a training mission. Photo: Air Force.
An Air Force U-2 flies a training mission. Photo: Air Force.

The plane went down about 9:05 a.m. Pacific time near the Sutter Buttes mountain range, the Air Force said. Investigators are trying to determine what caused the incident.

The Air Force’s history with the Lockheed Martin [LMT] U-2 Dragon Lady stretches back to the 1950s. As of September 2015, the service had an inventory of 33 U-2s.