An American Airlines plane with 64 people on board collided with an Army helicopter over Washington, D.C., and crashed into the Potomac River.

Among the questions is whether an Army helicopter deviated from its approved flight path before it collided with a passenger jet near Washington. An initial report found that the air traffic controller on duty was doing a job usually handled by two people.

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.