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.

The Army Black Hawk helicopter that collided with an American Airlines commuter plane near Reagan Washington National Airport in Virginia Wednesday was on a “training flight” when it crashed into the Potomac River, according to the military service branch.

He indicated 27 bodies had been recovered from the airplane, and one from the helicopter.