The crew of the Army Black Hawk helicopter that collided midair with an American Airlines plane near Washington, D.C., may not have realized they were flying too high or heard critical air traffic control messages before the fatal crash.

The Jan. 29 accident over the Potomac River killed all 67 people aboard.

The NTSB revealed that a key directive to “pass behind” the plane may have been missed due to radio interference.

Investigators are examining conflicting altitude data and why the Black Hawk’s ADS-B system was not transmitting, Fox News has reported.

The crew, likely using night-vision goggles, showed no audible reaction before impact.

Written by B.C. Begley