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 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.

Bradley Bowman, a former Army aviation officer, recalled flying a Black Hawk to retrieve Deputy Secretary of Defense Paul Wolfowitz, who was taken to a backup facility known as Raven Rock Mountain Complex, one of the U.S. government's main emergency sites.

Three black boxes — one from the Black Hawk helicopter and two from the American Airlines jet — have been recovered from the wreckage in Washington D.C.’s Potomac River, and are now being analyzed in labs. The helicopter’s box was recovered Friday after investigators previously recovered two black boxes from the jet.

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.

The military helicopter that collided with an American Airlines flight this week was conducting training to prepare for a catastrophe or attack on the US.

The Pentagon has launched its own investigation into how an Army Black Hawk helicopter collided with an American Airlines passenger plane over the Potomac River near Reagan Washington Regional Airport.