"On final approach into Reagan National it collided with a military aircraft on an otherwise normal approach," American Airlines CEO Robert Isom said. "At this time we don't know why the military aircraft came into the path of the ... aircraft."
Three soldiers were onboard the helicopter during a training flight, an Army official previously said.
Images from the river showed boats around the partly submerged wing and the mangled wreckage of the plane's fuselage.
Investigators will try to piece together the aircrafts' final moments before their collision, including contact with air traffic controllers as well as a loss of altitude by the passenger jet.