US Army Black Hawk near Washington found a key instrument on the helicopter was displaying inaccurate altitude data that could have led the pilots to think they were flying lower than they actually were.

A National Transportation Safety Board hearing revealed that the U.S. Army was aware of altitude discrepancies on Black Hawk helicopters.

Flight instruments probably led the Black Hawk crew to believe the helicopter was lower than it actually was before the collision with a commercial airplane on Jan. 29.