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.

The Black Hawk helicopter which collided with a passenger plane above Washington DC was training for a hypothetical doomsday scenario at the time, according to US officials. Three soldiers inside the military aircraft were killed as well as 64 people aboard the American Airlines jet.