Investigators have already recovered the cockpit voice recorder and flight data recorder of the American Airlines plane that collided with an Army helicopter as the plane was landing Wednesday night at Ronald Reagan National Airport next to Washington, D.C. Officials are scrutinizing a range of factors in what National Transportation Safety Board Chairwoman Jennifer Hommendy has called an “all-hands-on-deck event.”

All aboard the two aircraft were killed, with officials examining the actions of the military pilot as well as air traffic control after the helicopter apparently flew into the path of the American Airlines jet.

Air crash investigations can take months, and federal investigators told reporters Thursday they would not speculate on the cause.

Authorities were still looking for the helicopter’s black box recorder, Defense Secretary Pete Hegseth said Friday on Fox News Channel.

Other factors in the crash, including the helicopter’s altitude and whether the crew was using its night vision goggles, are still under investigation, Hegseth said.

At least 28 bodies have been pulled from the Potomac River.

The plane carried 60 passengers and four crew members, and three soldiers were aboard the helicopter.

One air traffic controller was responsible for coordinating helicopter traffic and arriving and departing planes when the collision happened, according to a report by the Federal Aviation Administration that was obtained by The Associated Press.

Those duties are often divided between two people, but the airport typically combines the roles at 9:30 p.m., once traffic begins to slow down.

On Wednesday the tower supervisor directed that they be combined earlier.

“The position configuration was not normal for the time of day and volume of traffic,” the report said.

A person familiar with the matter, however, said the tower staffing that night was at a normal level.

The positions are regularly combined when controllers need to step away from the console for breaks, during shift changes, or when air traffic is slow, the person said, speaking on the condition of anonymity to discuss internal procedures.

A person familiar with the matter, however, said the tower staffing that night was at a normal level.

The FAA has long struggled with a shortage of air traffic controllers.

Officials said flight conditions were clear as the jet arrived from Wichita, Kansas, carrying, among others, a group of elite young figure skaters, their parents and coaches, and four union steamfitters from the Washington area.

A top Army aviation official said the crew of the helicopter, a Black Hawk, was “very experienced” and familiar with the congested flying that occurs daily around the city.

Follow the NYP’s coverage of the deadly DC plane collision

“Both pilots had flown this specific route before, at night. This wasn’t something new to either one of them,” said Jonathan Koziol, chief of staff for Army aviation.

The helicopter’s maximum allowed altitude at the time was 200 feet (about 60 meters), Koziol said. It was not immediately clear whether it exceeded that limit, but Hegseth said altitude seemed to be a factor in the collision.

Koziol said investigators need to analyze the flight data before making conclusions about altitude.