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.

Black box recovered from Black Hawk helicopter as 41 bodies pulled from Potomac river - Questions grow about air safety in the US capital as Donald Trump says Black Hawk chopper was 'flying too high'