Federal investigators revealed Wednesday that the Black Hawk helicopter involved in the deadly DCA crash may have misreported its altitude by more than 100 feet, a flaw the Army had long known about but never formally documented.

The Army helicopter that collided with a plane over D.C. in January had incorrect altitude readings, contributing to the aircraft getting too close.

Safety investigators probing January’s midair collision between an American Airlines Group Inc. regional jet and a 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.