All 64 people aboard an American Airlines jet that collided with an Army helicopter were feared dead in what was likely to be the worst U.S. aviation disaster in almost a quarter century, officials said Thursday.

Transmissions show early instruction for an Army helicopter to avoid the passenger jet.

After American Airlines’ American Eagle Flight 5342 had a mid-air collision with a helicopter and subsequently crashed into the Potomac River, the D.C. fire chief shared a statement.