The U.S. Army helicopter that collided with an passenger jet near Washington, D.C., had an advanced surveillance system turned off.

Sixty-four people aboard a commercial airliner died Wednesday after it collided with a military helicopter midair near Reagan Washington National Airport. Both the American Eagle jet and Army Black Hawk are in the Potomac River.

The Black Hawk helicopter that crashed into an American Airlines flight was alerted to the plane’s presence by air control twice.