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 testimony, delivered during the first day of a multiday National Transportation Safety Board (NTSB) hearing, raised fresh concerns about whether Army pilots were given the information needed to safely navigate controlled airspace. The January collision between a UH-60L Black Hawk and an American Airlines jet killed 67 people, making it one of the deadliest air disasters in recent U.S. history.