NTSB investigators said they found that Black Hawk altimeters that measure flying height based on atmospheric pressure, known as barometric altimeters, showed a pilot that the aircraft was flying 80 to 130 feet lower than its actual altitude when over the Potomac River.
While federal investigators did not draw any conclusions from that information, the revelation raised questions about whether Capt. Rebecca Lobach, who was piloting the Black Hawk involved in the Jan. 29 accident, could have thought she was flying at a safe altitude instead of at a height that would send her helicopter directly into the path of a commercial jet that was descending toward the airport.
In an animation that re-created the minutes leading up to the crash, the NTSB showed that Lobach was flying above the maximum allowable height of 200 feet for nearly the entire duration of the time that the Black Hawk was maneuvering through the area around the airport. As it showed the Black Hawk and the American Airlines jet on a collision course, the animation included recordings of what air traffic controllers were telling the pilots of both aircraft and showed parts of the transcript of discussions taking place in the cockpit of the helicopter.
The materials and the testimony of helicopter experts were expected to provide the clearest picture to date about the extent to which faulty systems and human error contributed to the multiple failures that led to the crash.
Here’s what else to know:
— Altimeters: The NTSB’s new evidence sparked a layered debate about whether the discrepancies with the Black Hawk’s altitude readings could be considered cause for concern. Kylene Lewis, a chief warrant officer and helicopter test pilot with the Army, said that when flying below 200 feet she would normally rely on radar altimeters, which might have been more accurate. But she said she would also reference the barometric one when flying along routes with strict altitude limits, such as the one Lobach was flying along Jan. 29.
— Altitude discrepancies: Lewis also said that a discrepancy of about 100 feet between altimeters would not normally be cause for alarm and that she would only question the accuracy of her devices midflight if an air traffic controller raised a concern. She added under questioning that her testimony was based partly on her own experience and was not necessarily a specific part of training.
— Documents: Officials also released of a trove of more than 200 new documents and materials. They showed that the pilots seemed unaware of the impending danger until the final seconds before impact, when the pilots of the passenger plane tried to fly higher, while the pilots of the Black Hawk tried to maneuver east — a direction that might have allowed them to avoid crashing into the jet as it approached the airport.
This article originally appeared in The New York Times.