Officials are scrutinising 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 aircrafts 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 on Thursday they would not speculate on the cause.

Authorities were still looking for the helicopter’s black box recorder, Defence Secretary Pete Hegseth said on 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.

Military aircraft frequently conduct such flights in and around the nation’s capital for familiarisation with routes they would fly in case of a major catastrophe or an attack on the US that would require relocation of key officials from the capital region.

“You need to train as you fight, you need to rehearse in ways that would reflect a real world scenario,” Hegseth said.

He stressed that it remained the Pentagon’s duty to also mitigate risks, while conducting such training. But he underscored US forces need “to ensure, if unfortunately, there were a real world event where things needed to happen we could respond to it day or night.”

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 9.30pm, 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.

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.

“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 about 60 metres, 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 analyse the flight data before making conclusions about altitude.

President Donald Trump said in a Friday morning post on his Truth Social platform that the helicopter was “flying too high” at the time of the crash.

“It was far above the 200 foot limit. That’s not really too complicated to understand, is it???” Trump said. His comments come the day after he questioned the actions of a US Army helicopter pilot involved in the midair collision with a commercial airliner, while also blaming diversity initiatives for undermining air safety.

Flights at Reagan National resumed around midday Thursday.

Wednesday’s crash was the deadliest in the US since November 12, 2001, when an American Airlines flight slammed into a residential area of Belle Harbour, New York, just after takeoff from Kennedy Airport, killing all 260 people aboard and five people on the ground.

The last major fatal crash involving a US commercial airline occurred in 2009 near Buffalo, New York. Everyone aboard the Bombardier DHC-8 propeller plane was killed, along with one person on the ground, bringing the total death toll to 50.

But the airspace around Reagan National can challenge even the most experienced pilots no matter how ideal the conditions. They must navigate hundreds of other commercial planes, military aircraft and restricted areas around sensitive sites.

Just over 24 hours before the fatal collision, a different regional jet had to go around for a second chance at landing at Reagan National after it was advised about a military helicopter nearby, according to flight tracking sites and control logs. It landed safely minutes later.