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.

A key safety system was turned off on the US Army helicopter that collided with an American Airlines regional jet last week near Washington’s Reagan Airport, killing 67. Senate Commerce Committee chair Ted Cruz told reporters the Black Hawk helicopter had turned off its automatic dependent surveillance-broadcast (ADS-B),