Officials confirmed the crew of the Army Black Hawk helicopter that collided midair with an American Airlines passenger plane near Ronald Reagan Washington International Airport may not have known it was flying too high and may not have heard critical messages from air traffic control prior to the fatal crash.

The Jan. 29 crash over the Potomac River, which happened during an Army “flight check,” killed 67 people. There were no survivors.

National Transportation Safety Board (NTSB) Chair Jennifer Homendy said during a news conference Friday that critical messages from air traffic control, relayed to the Black Hawk just seconds before the crash, may have been missed.

Emergency workers recover debris from the Potomac River in the aftermath of a collision between American Eagle Flight 5342 and a Black Hawk helicopter.  (Reuters/Carlos Barria)

Homendy said the Army Black Hawk crew was likely wearing night-vision goggles throughout the flight, which could have affected what they were able to see in the dark near a bright airport.

“It’s going to be a factor in our visibility study,” she said. “We’re going to have to see what was possible for them to see at the time, leading up to the collision and the accident sequence.”

Recorder data shows there was no audible reaction from the Black Hawk crew prior to the crash, indicating they were not aware of the impending collision.