The U.S. Army has grounded all aviators not involved in critical missions. 

The decision comes after two recent helicopter crashes left 12 soldiers dead. The Army said during this period, pilots will focus on safety and training protocols. 

“The safety of our aviators is our top priority, and this stand down is an important step to make certain we are doing everything possible to prevent accidents and protect our personnel,” Army Chief of Staff James McConville said, according to the Associated Press.

On Thursday, two helicopters collided mid-air near Wainwright, Alaska, killing three soldiers and injuring another. Weeks before that, two helicopters crashed during a training mission near Fort Campbell, Kentucky, killing all nine soldiers aboard the aircraft. The incidents are still under investigation.