The pilots of a US army helicopter that collided with a passenger jet over Washington DC in January would have had difficulty spotting the plane while wearing night-vision goggles, experts told the National Transportation Safety Board (NTSB) on Friday.

The army goggles would have made it hard to see the plane’s colored lights, which might have helped the Black Hawk determine the plane’s direction. The goggles also limited the pilots’ peripheral vision as they flew near Ronald Reagan Washington national airport that evening.

The challenges posed by night-vision goggles were discussed at the NTSB’s third and final day of public testimony over the fatal midair crash, which left all 67 people