Two T-38 Talon jets were involved in a crash at an Air Force base in northwestern Oklahoma shortly after 9 a.m. Thursday, killing two airmen aboard, military officials said. The men were taking part in a training mission that ended with the deadly crash, whose cause has not yet been determined. The military hasn’t yet released the conditions of the others involved or the names of the two men who were killed in the crash, according to public affairs representative Zoe Perkins.

TV footage from the scene shows that one aircraft crashed upside down on grass near a runway, while the other crashed upright on the runway. This is the second crash involving a T-38 training jet in the past 15 months. In a 2018 western Oklahoma incident, a jet trainer developed engine trouble, then crashed and exploded while the Air Force pilot ejected successfully in time and was found safe.