Investigators have found that a helicopter involved in a deadly crash with a passenger plane over Washington was flying above its height limit.

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.

The National Transportation Safety Board said on Wednesday that testing showed faulty altitude data in U.S. Army helicopters like the one that collided with an American Airlines plane on January 29, killing 67 near Ronald Reagan Washington National Airport.