It still remains unknown what factors caused the deadly collision on 29 January between a US Army Sikorsky UH-60 Black Hawk and American Airlines flight 5342, but some theories have started to emerge.

Government officials, including secretary of defence Pete and President Donald Trump, seemed to indicate on 30 January that the army rotorcraft may have exceeded the altitude ceiling for rotary-wing aircraft operating along that stretch of the River near Ronald Reagan Washington National airport.

The incident involved a US Army Sikorsky UH-60 Black Hawk colliding with American Airlines flight 5342 – an regional jet operated by Airlines from Wichita, Kansas to Washington. The accident killed 67 people, including 60 passengers and four crew on the and three US Army personnel on the helicopter.

“We anticipate that the investigation will quickly be able to determine whether the aircraft was in the corridor and at the right altitude at the time of the incident,” said Hegseth.

That corridor is frequently used by military helicopters and the restrictions are meant to ensure safe separation with commercial air traffic in the crowded airspace.

The army has confirmed there is a ceiling of 200ft is in place for rotorcraft travelling along the Potomac River route in question.

“This is a standard operational limit set for safe flight in this controlled airspace,” the service says.

Notably, flight tracking information from flight 5342 indicates the regional jet was somewhere around 375ft when it stopped transmitting data.

Other possible explanations include the misidentification of the approaching commercial aircraft by the Black Hawk crew, perhaps due in part to the crew using night vision goggles.

Recordings of air traffic control communications reveal flight 5342 was directed to an alternate runway at Washington National shortly before landing. While that is not an uncommon occurrence, a retired UH-60 pilot tells the Associated Press the approach to runway 33 brings commercial aircraft much closer to – indeed, directly over – the designated helicopter flight corridor.

“I had that exact same incident several years ago,” former National Guard pilot Darrell Feller tells the news outlet. “There was a commercial jet landing on 33 and I could not see him. I lost him in the city lights.”

Washington National airport sits in the midst of a dense urban area including Washington and the neighbouring cities of Alexandria and Arlington in Virginia. Numerous highways cross the area.

“Moving lights get mixed up with ground lights,” Feller notes.

The approach to runway 33 would have placed the incoming at an oblique angle to the oncoming UH-60, meaning the regional jet’s approach lights would not pointed directly at the helicopter’s crew, he adds.

The collision happened around 20:48 local time while the Black Hawk crew was performing a regular night proficiency flight with night vision goggles (NVGs) – standard practise for US Army night flights.

Some experts have speculated that the night vision equipment may have contributed to the disaster. The goggles work by enhancing ambient light sources that are too dim for the naked eye, such as stars. When worn in a bright environment such as a cityscape, can quickly blind a wearer.

“Goggles actually make it worse down there,” Feller notes of the area around Washington National. “A lot of times we would flip our goggles up going through that area.”

The army on 31 January confirmed the flight crew of the incident UH-60 were operating with NVGs. However, the service notes that “flying unaided was also an option”, due to the well-lit nature of the flight route.

Feller adds that the high volume of commercial air traffic coming into the waterfront airport also poses a challenge to rotorcraft on the Potomac corridor, creating potential for pilots to mistakenly identify inbound flights.

Whether the UH-60 crew misidentified another aircraft as the remains unknown, but the crew had been advised of the CRJ’s presence as the jet prepared to manoeuvre for the runway change. Using the helicopter’s call sign, ‘PAT25’, a controller referred to traffic “just south” of the Woodrow Wilson Bridge, identifying the aircraft as a a CRJ and giving its altitude and saying the jet was “[preparing] for runway 33”.

The helicopter crew responded that the traffic was “in sight” and requested visual separation – a procedure under which the pilot is responsible for maintaining safe distance.

Investigators from the National Transportation Safety Board (NTSB) say they will not release a preliminary report into the cause of the collision for at least 30 days.

The has already recovered the cockpit voice recorder and flight data recorder from the CRJ700, but not yet equipment from the army UH-60.

The two Black Hawk pilots had a combined 1,500h of flight time between them, according to army.

Lead pilot Chief Warrant Officer 2 Andrew Eaves had logged 1,500h of flight time over his career, while co-pilot Captain Rebecca had accrued 500h.

Warrant officers are typically assigned to highly technical specialities such as aviation and intelligence. Aviation warrant officers often serve as lead pilots, and training less-experienced officers like captains and lieutenants, who spend less of their careers flying and typically have more administrative responsibility.

The identity of the third individual aboard the UH-60 – the crew chief – has been confirmed as Staff Sergeant Ryan O’Hara.

American Airlines chief executive Robert Isom says the CRJ700’s pilots also had significant experience.

The regional jet’s captain had flown for for six years, while the first officer had two years on the job, according to Isom. “These are experienced pilots.”

Story updated on 1 February to include additional details on the PAT25 crew provided by the US Army