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

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.

Forty-one sets of remains have been recovered and 28 of those victims have been positively identified, Washington, D.C., Fire and EMS Chief John Donnelly Sr. said at a news conference Friday. Next of kin notifications had been made to 18 families as of 6 a.m. Friday, he said.