Before an Army Black Hawk crashed into a passenger jet on the night of Jan. 29, the helicopter pilots told the air traffic controller guiding them near Ronald Reagan National Airport that they saw a nearby jet and would steer clear of it.

But experienced Army aviators told the National Transportation Safety Board during hearings on Friday that American Airlines Flight 5342 might have been difficult for the helicopter pilots to keep in their sights.

Federal investigators will release their findings early next year about the cause of the midair collision, which killed 67 people — the worst airplane crash in the United States in nearly a quarter-century. But one question is whether the Army pilots ever actually saw the airplane that the air traffic controller flagged in his communications with them that night.

In their testimony Friday, Army experts explained why that might have been difficult for the pilots, Capt. Rebecca M. Lobach, who was undergoing her annual flight evaluation, and her instructor, Chief Warrant Officer 2 Andrew Loyd Eaves.

At night, light pollution from Washington, the Pentagon and the airport itself is a common problem for pilots. It can be worse when flying with night-vision goggles, as the Army pilots were using on the night of the crash, the aviators said. Further complicating matters were exterior lights on the commercial jet that were dimmer than those on more modern planes. Even the configuration of the Black Hawks can cause sightline problems.

All those factors could have complicated the Black Hawk pilots’ ability to keep their eyes on the correct airplane, even after telling the air traffic controller they could see it.