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.

Meanwhile, the authorities also recovered some additional parts of the American Airlines plane that was about to land at the Reagan National Airport when it collided with the helicopter

The Black Hawk helicopter that collided with a passenger jet in Washington on Wednesday was on a training flight along a route core to a seldom-discussed military mission to evacuate senior officials to safety in the event of an attack on the U.S., officials say.

Search teams scoured the Black Hawk helicopter wreckage after the Potomac River mid-air collision with a plane. A group of investigators conducted an inspection in the frigid waters where the military chopper crashed into a plane before plunging into the Potomac River.