The black boxes for a commercial flight that crashed into a military helicopter in Washington DC have been located, as questions mount about staffing and other close calls at the airport where the plane was landing.

Normally two people manage air traffic control for helicopters and airplanes flying in the area – one of the most controlled airspaces in the world – but only one person was doing so on Wednesday at the time of the crash, according to sources cited by the BBC’s US partner CBS News.

Officials are still investigating the cause of the incident that killed all 67 people aboard the two aircraft.

The National Transportation Safety Board (NTSB) said a preliminary report will be issued in 30 days.

The flight data recorder and the cockpit voice recorder, known as the black boxes, can help offer clues to investigators about what may have gone wrong on the flight.

The boxes will be transported to the NTSB lab, nearby the site of the crash, and analysed, according to CBS.

The air traffic control staffing numbers, first reported by the New York Times, was noted as “not normal”, according to a preliminary Federal Aviation Administration (FAA) report.

The federal government has struggled for years to fill certain key positions at the FAA.

The type of staffing that had one air traffic control worker managing both the helicopters and planes at the Regan Washington National Airport on Wednesday night is reportedly not uncommon and did not breach guidelines.

Divers spent most of Thursday swimming through the icy waters of the Potomac River, searching for the bodies of victims.

The search was suspended on Thursday evening due to dangerous conditions.

There were 64 passengers aboard the American Airlines flight that collided with an Army Black Hawk helicopter that was on a training mission flight. Three soldiers were on board.

Teams have so far recovered 27 bodies from the plane and one from the helicopter.

At a White House briefing on Thursday, President Donald Trump began with a moment of silence and a prayer for victims.

He said “we can only begin to imagine the agony that you’re all feeling”, adding, “our hearts are shattered alongside yours”.

Trump speculated on the cause of the collision, suggesting without evidence that lower hiring standards for air traffic controllers in the FAA under previous administrations run by Democrats may have been a factor.

Later on Thursday, he signed a memorandum to end diversity, equity and inclusion (DEI) practices in the aviation sector.

DEI programmes aim to promote participation in workplaces by people from a range of backgrounds. Backers say they address historical or ongoing discrimination and underrepresentation but critics argue they can themselves be discriminatory.

Trump also signed an executive order to appoint a new head of the FAA.

The fatal incident happened at about 21:00 local time (02:00 GMT) on Wednesday, when a PSA Airlines jet operating as American Airlines 5342 collided mid-air with a US Army helicopter as it approached Ronald Reagan Washington National Airport.

Both aircraft careened into the Potomac River. The passenger plane broke into multiple pieces and sank several feet into the water, while the helicopter ended up upside down in the river.

The plane, a Bombardier CRJ700, had departed from Wichita, Kansas, and was carrying dozens of passengers, including a pair of young figure skaters, their mothers, and two Russian coaches.

Kremlin spokesman Dmitry Peskov was quoted in Russia media saying: “There were other of our fellow citizens on board. It’s bad news today from Washington.

“We are sorry and send our condolences to families and friends.”

The helicopter was a Sikorsky H-60 that took off from Fort Belvoir in Virginia with three soldiers on board, and belonged to B Company, 12th Aviation Battalion.

“It’s a tragedy, a horrible loss of life for those 64 souls on that civilian airliner, and of course the three soldiers in that Black Hawk [helicopter],” said new defence secretary Pete Hegseth on Wednesday.

Donald Trump stood before the White House press room cameras on Thursday to perform a traditional presidential duty – consoler-in-chief during a time of tragedy.

He said the country was in mourning, shared his condolences during “an hour of anguish” and paid tribute to first responders and the victims.

Then he sharply pivoted – providing yet another reminder of how his new presidency is going to be very different.

It will be combative. It will be unscripted. And it will be quick to point the finger of blame.

“We do not know what led to this crash, but we have some very strong opinions and ideas,” he said.

He then speculated that lowered standards of hiring for air traffic controllers in the Federal Aviation Administration during the Joe Biden and Barack Obama presidencies may have been a factor in the disaster.

• LIVE UPDATES: Get the latest on the crash investigation
• US and Russian figures skaters were on board plane

Trump and his fellow Republicans have regularly attacked “diversity, equity and inclusion” programmes in the federal government.

His team has made undoing such programmes a core part of their first days in office, saying they have divided Americans and weakened the country.

And less than 24 hours after the first major US air disaster in more than a decade, Trump – along with his secretaries of transportation and defence, and his vice-president – took turns hammering their point, even as they provided no evidence that federal hiring practices had any connection to this particular crash.

Asked by a reporter how he could blame diversity programmes for the crash when the investigation had only just begun, the president responded: “Because I have common sense.”

At other moments, he acknowledged there was no confirmed cause, saying “it’s all under investigation”.

Trump said the hiring guidance for the FAA’s diversity and inclusion programme included preference for those with disabilities involving “hearing, vision, missing extremities, partial paralysis, complete paralysis, epilepsy, severe intellectual disability, psychiatric disability and dwarfism”.

An archived version of a website for the FAA’s diversity and inclusion hiring programme that appears to have been taken down in December included a similar list. The agency was seeking people with “targeted disabilities” that the federal government was prioritising for recruitment at the time.

But it’s unclear how that drive to make recruitment more diverse may have impacted the ranks of air traffic controllers, who President Trump said needed to all be “naturally talented geniuses”. The FAA has more than 35,000 employees, only a fraction of which perform that role.

In response to criticisms over diversity hiring practices last year, the agency released a statement asserting that all new hires must meet “rigorous qualifications” that “vary by position”.

The agency has faced criticism over a longstanding shortage of air traffic controllers, particularly after the Covid-19 pandemic caused massive disruptions in commercial air travel.

Reports suggest that staffing levels at Reagan airport on Wednesday night may have been compromised.

In his remarks, Trump specifically blamed Biden administration Transportation Secretary Pete Buttigieg, whom he described with an obscenity and said had ran the department “into the ground”.

Buttigieg defended his record on social media, calling Trump’s comments “despicable”. “As families grieve, Trump should be leading, not lying,” he said.

Senate Democratic Leader Chuck Schumer also criticised Trump’s comments.

“It’s one thing for internet pundits to spew off conspiracies, it’s another for the President of the United States to throw out idle speculation as bodies are still being recovered,” Schumer said.

Once he departed from his prepared remarks, however, speculation was what President Trump seemed most interested in offering.

Along with his condemnation of DEI policies, he offered extended discussion of the angles and elevation at which the two aircraft were flying, the weather conditions on Wednesday night, the temperature of the Potomac and the behaviour of the Army helicopter.

“We had a situation where we had a helicopter that had an ability to stop,” he said. “For some reason, it just kept going.”

But on Thursday evening, the White House doubled down on blaming his predecessor and DEI policies. The president signed a memorandum to end diversity efforts in the aviation sector and to review all hiring decisions and changes to safety protocols made during the Biden administration. He also signed an executive order to appoint a new head of the FAA.

Two things were very clear from Trump’s remarks on Thursday.

The first is that his eagerness to inject himself into a major news story is undiminished in his new term. And the second is that in his view it is never too soon to inject politics into national tragedy – and use it to attack opponents and advance his agenda.