Clues emerging from the moments before the deadly collision Wednesday night between an Army helicopter and an American Airlines passenger jet suggest that multiple layers of the country’s aviation safety apparatus failed, according to flight recordings, a preliminary internal report from the Federal Aviation Administration, interviews with current and former air traffic controllers and others briefed on the matter.

The helicopter flew outside its approved flight path. The American Airlines pilots most likely did not see the helicopter close by as they made a turn toward the runway. And the air traffic controller, who was juggling two jobs at the same time, was unable to keep the helicopter and the plane separated.

An F.A.A. spokesman said the agency could not comment on the ongoing investigation, which is being led by the National Transportation Safety Board. Crash investigators will spend the next several months reviewing flight data, recordings from inside the cockpits, weather patterns, as well as interviewing controllers and others involved to try to figure out what went wrong.

But the catastrophe already appeared to confirm what pilots, air traffic controllers and safety experts had been warning for years: Growing holes in the aviation system could lead to the kind of crash that left 67 people dead in the Potomac River in Washington.

Even before an official cause is determined, there were signs Wednesday that pilots and air traffic controllers at Reagan National were not operating under optimal conditions.

The duties of handling air traffic control for helicopters and for planes at Reagan National on Wednesday night were combined before the deadly crash. That left only one person to handle both roles, according to a person briefed on the staffing and the report.

Typically one person handles both helicopter and plane duties after 9:30 p.m., when traffic at Reagan begins to lessen. But the supervisor combined those duties sometime before 9:30, and allowed one air traffic controller to leave, according to the person, who was not authorized to speak publicly about the investigation into the crash. The crash occurred just before 9 p.m.

While there were no unusual factors causing a distraction for controllers that night, staffing was “not normal for the time of day and volume of traffic,” the preliminary F.A.A. report said.

On Thursday, five current and former controllers said that the controller in the tower should have more proactively directed the helicopter and the plane to fly away from each other. Instead, the controller asked the helicopter to steer clear of the plane.

Some of the current and former controllers said the darkness could have made it more difficult for pilots to accurately gauge the distance between themselves and other aircraft. Some wondered whether the helicopter pilots mistook a different plane for the American jet.

The helicopter was supposed to be flying closer to the bank of the Potomac River and lower to the ground as it traversed the busy Reagan National airspace, four people briefed on the incident said.

Before a helicopter can enter any busy commercial airspace, it must get the approval of an air traffic controller. In this case, the pilot asked for permission to use a specific, predetermined route that lets helicopters fly at a low altitude along the bank on the east side of the Potomac, a location that would have let it avoid the American Airlines plane.

The requested route — referred to as Route 4 at Reagan National — followed a specific path known to the air traffic controller and helicopter pilots. The helicopter confirmed visual sight of a regional jet and the air traffic controller instructed the helicopter to follow the route and fly behind the plane.

But the helicopter did not follow the intended route, the people briefed on the matter said.

Rather, it was above 300 feet, when it was supposed to be flying below 200 feet, and it was at least a half-mile off the approved route when it collided with the commercial jet.

A senior Army official urged caution in making any assessments until the helicopter’s black box could be recovered and analyzed, along with other forensic data.

The official, who spoke on condition of anonymity because of the ongoing inquiry, said the Black Hawk’s pilots had flown this route before, and were well aware of the altitude restrictions and tight air corridor they were permitted to fly in near the airport.

Safety lapses in aviation have been increasing for years, leading to an alarming pattern of close calls in the skies and at airports involving commercial airlines. They have occurred amid rising congestion at the country’s busiest airports, including Reagan National, where the frequent presence of military flights makes controlling traffic even more complicated.

At the same time, a chronic shortage of air traffic controllers has forced many to work six-day weeks and 10-hour days — a schedule so fatiguing that multiple federal agencies have warned that it could impede controllers’ abilities to do their jobs properly. Few facilities have enough fully certified air traffic controllers, according to a Times investigation in 2023. Some controllers say little has improved since then.

The air traffic control tower at Reagan National has been understaffed for years. The tower there was nearly a third below targeted staff levels, with 19 fully certified controllers as of September 2023, according to the most recent Air Traffic Controller Workforce Plan, an annual report to Congress that contains target and actual staffing levels. The targets set by the F.A.A. and the controllers’ union call for 30.

An F.A.A. spokesman said on Thursday that Reagan National currently employs 25 certified controllers out of their goal of 28.

The controller who was handling helicopters in the airport’s vicinity Wednesday night was also instructing planes that were landing and departing from its runways. Those jobs are typically assigned to two controllers, rather than one, the internal F.A.A. report said. This increases the workload for the air traffic controller and complicates the job.

Controllers can also use different radio frequencies to communicate with pilots flying planes and pilots flying helicopters. While the controller is communicating with pilots of the helicopter and the jet, the two sets of pilots may not be able to hear each other.

As the passenger jet’s pilots were approaching the airport, they were asked by air traffic control to pivot the landing from one runway to another, according to the F.A.A. report, a person briefed on the incident and audio recordings of conversations between an air traffic controller and the pilots. That request may have introduced another complication shortly before the collision.

The American Airlines flight had originally been cleared by the traffic control tower to land on the airport’s main runway, called Runway 1. The controller then asked the pilot to land on a different, intersecting runway instead — Runway 33 — which the pilot agreed to do.

That decision, according to the person who was briefed on the incident and four other people who are familiar with the airport’s air traffic, happens routinely when regional jets like the American Airlines aircraft are involved. The decision may also have been made to help keep air traffic moving efficiently by not clogging the main runway, the people said.

Runway 33 is shorter, requiring intense focus from pilots landing their planes. The last-minute change raised questions within the F.A.A. on Thursday morning about congestion at Reagan National, the person briefed on the event added.

Robert Isom, American’s chief executive, said at a news conference on Thursday that the pilots of the passenger plane involved in the crash had worked for PSA Airlines, an American subsidiary, for several years, The captain had been employed by the airline for almost six years, while the first officer had worked there for almost two years.

“These were experienced pilots,” he said.

Nicholas Bogel-Burroughs contributed reporting.