It is clear that something went terribly wrong the night of Jan. 29, when an Army Black Hawk helicopter collided with an American Airlines regional jet over the Potomac River near Ronald Reagan National Airport, killing everyone on board the aircraft.
But one error did not cause the worst domestic crash in the United States in nearly a quarter-century. Modern aviation is designed to have redundancies and safeguards that prevent a misstep, or even several missteps, from being catastrophic. On Jan. 29, that system collapsed, a New York Times investigation found.
Up to now, attention has focused on the Black Hawk’s altitude, which was too high and placed it directly in the jet’s landing path. But The Times uncovered new details showing that the failures were far more complex than previously understood.
Here are five takeaways from the investigation:
The Black Hawk crew failed to effectively execute a common but sometimes dangerous aviation practice.
The practice, known as flying under see and avoid rules, works exactly as it sounds. A pilot is meant to see neighboring air traffic, often without assistance from the air traffic controller, and avoid it by hovering in place until the traffic passes or by flying around it in prescribed ways.
One benefit of the see-and-avoid system is that it can lighten the controller’s workload during busy periods. But see and avoid has proved problematic, even deadly, in recent decades. It has also been implicated in at least 40 fatal collisions since 2010, according to the National Transportation Safety Board.
On the night of the crash, the Black Hawk crew did not execute see and avoid effectively. The pilots either did not detect the specific passenger jet the controller had flagged, or could not pivot to a safer position. The result is that they flew directly into the path of American Airlines Flight 5342 as it tried to land at National Airport.
The air traffic controller could have given a more urgent warning that the two aircraft were converging.
Though the air traffic controller on duty that night had delegated the prime responsibility for evading other air traffic to the Black Hawk crew, he continued to monitor the helicopter, as his job required. Yet he did not issue clear, urgent instructions to the Black Hawk to avert the crash, aviation experts say.
As the two aircraft moved closer to each other, the controller issued an instruction to the helicopter crew: Pass behind the airplane.
Some former military pilots said that by issuing that command, the controller was going above and beyond his obligations, especially under see-and-avoid conditions, and that an experienced Black Hawk crew should have known what to do without help.
Still, some regulators and controllers said that the controller in this case could have done more.
He could have told the Black Hawk crew where Flight 5342 was positioned and which way it was bound. (The Federal Aviation Administration manual instructions direct controllers to use the hours of a clock in describing locations.) He also could have provided the jet’s distance from the helicopter in nautical miles or feet.
But one thing is critical. When two aircraft are on a collision course, the controller’s top priority must be to warn both sets of pilots. “Advise the pilots if the targets appear likely to merge,” F.A.A. regulations state.
That did not happen.
Technology did not work as intended.
Radio communications, the tried-and-true means of interaction between controllers and pilots, also broke down. Some of the controller’s instructions were “stepped on” — meaning that they cut out when the helicopter crew pressed a microphone to speak — and important information likely went unheard.
Technology on the Black Hawk that would have allowed controllers to better track the helicopter was turned off. The Black Hawk did not operate with the technology because of the confidentiality of the mission for which its crew was practicing. That is because the helicopter’s positions can be obtained by anyone with an internet connection when the technology is turned on, making it a potential risk to national security.
As a result, the controller relied on pings from the helicopter’s transponder to show its changing location on the radar, which can take between five and 12 seconds to refresh, according to F.A.A. documents.
In a busy airspace, that lapse, said Michael McCormick, a former vice president of the F.A.A. Air Traffic Organization, is “a very long time.”
The route the helicopter was flying and the runway the jet was using to land formed a particularly dangerous combination.
Near the end of his shift, the controller handling both helicopters and commercial jets tried to pull off a complicated, and potentially risky, maneuver controllers refer to as a squeeze play.
That is an attempt to keep operations moving efficiently by tightly sequencing runway traffic with minimal time between takeoffs or landings, according to veteran National Airport controllers.
The landing of Flight 5342 from Wichita, Kan., was supposed to be a part of that maneuver. In order to pull it off, the controller evidently decided to land that flight not on the commonly used Runway 1, but the little-used Runway 33.
Runway 33 had a quirk: a particularly narrow vertical space between the landing slope for a jet and the maximum altitude at which helicopters using a certain route, called Route 4, could fly.
At its highest, near the Potomac’s east bank, the vertical distance between a helicopter and an aircraft en route to landing on Runway 33 would be 75 feet, N.T.S.B. investigators said. But if a helicopter were flying farther from the river’s east bank toward the airport, that distance would be even less.
With so little margin for error, it would be crucial that the helicopter fly below the maximum altitude for the route.
The Black Hawk that night was flying higher than that, putting everyone in both aircraft in peril.
The Black Hawk pilot failed to heed a directive from her co-pilot to change course.
The Army crew’s mission was to conduct an annual evaluation of Capt. Rebecca M. Lobach, to ensure that her helicopter piloting skills were up to par.
That night, her assignment was to navigate the conditions of a scenario in which members of Congress or other senior government officials might need to be carried out of the nation’s capital in the event of an attack. Chief Warrant Officer 2 Andrew Loyd Eaves was her instructor.
In the final seconds before impact, Warrant Officer Eaves told Captain Lobach that the air traffic controller wanted her to turn left.
Turning left would have opened up more space between the helicopter and Flight 5342, which was heading for Runway 33 at an altitude of roughly 300 feet. But there is no indication that she ever turned left. Instead, the helicopter flew directly into the jet.
