Four Army aviators were killed when their UH-60 Black Hawk crashed Monday evening on Fort Hood, Texas, officials said.

The helicopter crashed sometime after 5:49 p.m. Central time in the northeast portion of the Fort Hood Range. The crew was on a routine training mission at the time of the crash.

All four soldiers on board died; they were assigned to Division West, First Army, according to information from the Army. Their names will not be released until their families are notified.

Emergency crews found the crash site after an extensive search. The cause of the crash is unknown, and it remains under investigation.

Monday was a deadly day for Army aviation. The crash at Fort Hood was the second helicopter crash suffered by the Army on the same day. Earlier Monday, an AH-64 Apache helicopter crashed in South Korea. Two aviators died in that incident.