The BBC's Analysis Editor Ros Atkins on the unanswered questions around a fatal crash between a commercial airplane and a military helicopter near Washington DC.

Officials believe there are no survivors after a passenger plane on approach to Reagan National Airport near Washington, DC, collided Wednesday night with a US Army helicopter midair, sending both aircraft into the Potomac River below,

An American Airlines regional passenger jet and a U.S. Army Black Hawk helicopter collided midair and crashed into the Potomac River near Reagan Washington National Airport on Wednesday night. Officials have not provided a death toll but said all passengers and crew on both flights were feared dead.