Divers are expected to return to the Potomac River as part of the recovery and investigation after the United States' deadliest aviation disaster in almost a quarter century.

Air crash investigations can take months, and federal investigators told reporters they would not speculate on the cause.

Emergency teams will continue efforts to retrieve the bodies of those who died when a passenger jet and helicopter collided.

An American Airlines regional jet went down in the Potomac River near Ronald Reagan Washington National Airport.