As they flew south along the Potomac River on the gusty night of Jan. 29, the crew aboard an Army Black Hawk helicopter attempted to execute a common aviation practice. It would play a role in ending their lives.

Shortly after the Black Hawk passed over Washington’s most famous array of cherry trees, an air traffic controller at nearby Ronald Reagan National Airport alerted the crew to a regional passenger jet in its vicinity. The crew acknowledged seeing traffic nearby.

One of the pilots then asked for permission to employ a practice called “visual separation.” That allows a pilot to take control of navigating around other aircraft, rather than relying on the controller for guidance.

“Visual separation approved,” the controller replied.

The request to fly under those rules is granted routinely in airspace overseen by controllers. Most of the time, visual separation is executed without note. But when mishandled, it can also create a deadly risk — one that aviation experts have warned about for years.

On Jan. 29, the Black Hawk crew did not execute visual separation effectively. The pilots either did not detect the specific passenger jet the controller had flagged or could not pivot to a safer position. Instead, one second before 8:48 p.m., the helicopter slammed into American Airlines Flight 5342, which was carrying 64 people to Washington from Wichita, Kansas, killing everyone aboard both aircraft in a fiery explosion that lit the night sky over the river.

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.“Multiple layers of safety precautions failed that night,” said Katie Thomson, the Federal Aviation Administration’s deputy administrator under President Joe Biden.

The New York Times examined public records and interviewed more than 50 aviation experts and officials, to piece together the most complete understanding yet of factors that contributed to the crash.

Up to now attention has focused on the Black Hawk’s altitude, which was too high and placed the helicopter directly in the jet’s landing path at National Airport.

Not only was the Black Hawk flying too high, but in the final seconds before the crash, its pilot failed to heed a directive from her co-pilot, an Army flight instructor, to change course.

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. Doing so was Army protocol, meant to allow the pilots to practice secretly whisking away a senior government official in an emergency. But at least some experts believe that turning off the system deprived everyone involved of another safeguard.

The controller also could have done more.

Though he had delegated the prime responsibility for evading other air traffic to the Black Hawk crew under visual separation, 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.

The FAA said in a statement that it could not discuss “any aspect” of a continuing investigation led by the National Transportation Safety Board.

Investigators from the NTSB will issue their final report on the causes of the crash by early 2026.

Two departures

At 6:39 p.m. Eastern Standard Time, a CRJ700 regional jet departed Wichita under cool, dry conditions with 60 passengers, two pilots, Capt. Jonathan J. Campos and Sam Lilley, and two flight attendants on board. It was operated by American Airlines’ subsidiary carrier, PSA Airlines, and the direct route to National Airport had started the previous January.

Six minutes after Flight 5342 departed, the Black Hawk took off from Davison Army Airfield, at Fort Belvoir, Va., about 20 miles southwest of Washington.

It was crewed by Capt. Rebecca M. Lobach, the highest-ranking soldier on the helicopter; Chief Warrant Officer 2 Andrew Loyd Eaves, who was acting as her instructor; and Staff Sgt. Ryan Austin O’Hara, whose job was to help with equipment and other technical issues.

A little after 8:30 p.m., an Army helicopter, known in the tower as a “PAT” for priority air transport, made contact with the air traffic controller at the National Airport.

The controller had worked for the FAA for about a decade in two smaller air-traffic control centers, but had been stationed at National Airport for about two years.

After a co-worker left the control hub at 3:40 p.m., some controllers began to assume combined duties. The controller who ended up directing the Black Hawk took over combined duties at roughly 7 p.m., according to the government document. An NTSB spokesperson declined to confirm how long the controller operated in both roles.

The controller could not watch the helicopter’s movements in real time, because the crew was practicing for a confidential mission, and was not using an aviation broadcasting system which reports an aircraft’s position, altitude and speed roughly every second.

As a result, the controller relied on pings from the helicopter’s transponder to show its changing location, which can take between five and 12 seconds to refresh, according to FAA documents.

Little margin

The controller handling both helicopters and commercial jets tried to pull off a complicated, and potentially risky, maneuver called a squeeze play, to keep operations moving efficiently, according to veteran National Airport controllers, by tightly sequencing runway traffic.

The controller asked to divert the American Airlines landing to one of the airport’s ancillary runways.

“Yeah, we can do, uh, three-three,” one of the pilots replied.

The new runway had 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.

With so little margin for error — 75 feet or even less — it would be crucial that the Black Hawk fly below the maximum altitude for the route.

Aboard the Black Hawk, Lobach announced an altitude of 300 feet, according to cockpit voice recordings. Eaves then read out an altitude of 400 feet.

The FAA mandated an altitude of no higher than 300 feet for that part of the route, meaning that an altitude of 400 feet would have been unacceptable and could have positioned the Black Hawk uncomfortably close to departing or landing airplanes.

As the helicopter approached the Key Bridge, from which it would fly south along the river, Eaves stated that it was at 300 feet and descending to 200 feet.

Seconds after the Black Hawk crossed over the Tidal Basin, a shallow lake near the Washington Monument ringed by cherry trees, the controller informed the Army crew that a regional jet — Flight 5342 — was “circling” to Runway 33.

Investigators now believe that the word “circling” was not heard by the Black Hawk crew because one of them was pressing the microphone key to speak when the word came through their radios. If the key is depressed, the pilot can speak but not hear incoming communications.

Around 8:46 p.m., Eaves responded to whatever he did hear of the circle-landing notification, using the call sign for his own flight: “PAT two-five has traffic in sight. Request visual separation.”

The controller gave his approval.

In the 90 seconds after the air traffic controller granted visual separation to the Black Hawk, the attempted squeeze play started to unfold. At 8:46:48 p.m. the tower cleared a jet for immediate departure off Runway 1.

Then, the Black Hawk, still southbound, passed Hains Point, a park area along the east side of the Potomac, moving it closer to the airport on the opposite bank.

“PAT two-five, do you have the CRJ in sight?” he asked, using the abbreviation for the model of Flight 5342’s aircraft.

The controller received no response. The helicopter and Flight 5342 were by then about 1 mile apart.

The controller then issued an instruction to the helicopter crew: Pass behind the airplane.

Cockpit voice recordings indicate that the essence of the controller’s command — to “pass behind” — might not have been heard by the Black Hawk crew, perhaps because of a second bleep-out.

Direct, immediate intervention was needed that night. Instead of seeing and avoiding Flight 5342, Lobach continued flying straight at it.

Investigators might never know why. There is no indication that she was suffering from health issues at the time or that a medical event affected her during those final moments aboard the Black Hawk, according to friends and people familiar with the crash investigation, which included autopsies and performance log reviews.

Two seconds after the controller’s cut-out instruction about passing behind the jet, Eaves replied, affirming for the second time that the Black Hawk saw the traffic.

It was their last communication.