A key safety system was turned off on a U.S. Army helicopter that collided with an American Airlines regional jet last week near Washington Reagan Airport, killing 67.

Investigators trying to determine what caused last week’s deadly midair collision between a US military Black Hawk helicopter and an American Airlines plane near Washington, DC, briefed lawmakers Thursday on what they’ve learned after combing through data from both aircraft and air traffic control.

Readings have been compared from the black box recovered from American Eagle flight 5342 and the air traffic control tower about the Black Hawk helicopter