There was confusion between the pilot and air traffic control before Nepal's deadliest plane crash in decades on Monday, recordings seem to show.
Aviation authorities said they had recovered the flight data recorder from the charred wreckage of the plane, which burst into flames after crashing into a football field near Kathmandu airport, killing 49 people.
Witnesses have described how the US-Bangla Airways plane carrying 71 people abruptly changed direction moments before it crashed.
On Monday, the airline's chief executive, Imran Asif, said there had been a "fumble from the control tower" as the plane approached the airport's single runway.
But airport manager Raj Kumar Chhetri said it was too early to say what had caused the mountainous country's deadliest crash since 1992.
"It is yet to be identified whether the pilot or air traffic control was wrong," he said. He said the investigation would be carried out with Bangladesh.
Recordings of the conversation between air traffic control and the pilot appear to indicate confusion over which end of Kathmandu airport's single runway the plane was to approach.
Air traffic control can initially be heard clearing the plane to land from the southern approach.
"You are going toward runway 20," the controller is heard saying seconds later, referring to the northern end of the tarmac.
A series of confused messages follow just before the crash, in which the pilot says they will land at "runway 20" and then "runway 02" – the southern end.
"There is certainly considerable confusion from air traffic as to which runway the aircraft actually wants to land on," said aviation expert Andrew Blackie, who has reviewed the recordings.
Read more: At least 49 killed in Kathmandu plane crash
Survivors said the pilot gave no warnings as the plane abruptly changed direction.
"I had asked the air hostess, what is happening, is everything fine? She gave a thumbs up, but I could see she was panicking," said Ashish Ranjit, 35, who escaped through a window on the plane's right.
"It was so low and it took such sharp turns."
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Rescue teams next to the wreckage of a plane that crashed at the main airport Tribhuvan International Airport in Kathmandu, Nepal. Narendra Shrestha / EPA -
US-Bangla Airlines flight was arriving from Dhaka, Bangladesh. Navesh Chitrakar / Reuters -
The crash happened one day after a Turkish plane with 11 people on board, all women, crashed in Iran. Navesh Chitrakar / Reuters -
"The chances of rescuing anyone (else) alive is slim now because the plane was badly burned," said army spokesman Gokul Bhandaree who said at least 40 people were killed. Navesh Chitrakar / Reuters -
Smoke rises following the crash of a Bangladeshi aircraft at Kathmandu airport, Nepal on March 12, 2018. Rusha Giri / via Reuters -
Smoke rises following the crash of a Bangladeshi aircraft at Kathmandu airport, Nepal. Rusha Giri / via Reuters -
People stand as smoke rises following the crash of a Bangladeshi aircraft at Kathmandu airport. Nitin Keyal / via Reuters -
Nepalese rescuers stand near a passenger plane from Bangladesh that crashed at the airport in Kathmandu, Nepal. Niranjan Shreshta / AP Photo -
Wreckage of an airplane is pictured as rescue workers operate at Kathmandu airport, Nepal. Navesh Chitrakar / Reuters -
Wreckage of an airplane is pictured as rescue workers operate at Kathmandu airport, Nepal. Navesh Chitrakar / Reuters
The plane hit the runway and skidded through an airport fence, leaving a trail of fuel and coming to a stop in a field where it burst into flames.
Twenty-two passengers – mostly sitting on the plane's right side – managed to free themselves from burning wreckage by climbing through the windows or were pulled from the fuselage by passengers and rescuers.
Kathmandu airport lies in a bowl-shaped valley with the Himalayas to the north, making it a notoriously challenging place to land.
Nepal has a poor road network and internal flights are key to accessing remote parts of the Himalayan nation.
It has suffered more than 20 aviation accidents in the last decade, mostly involving small planes on domestic routes.
"There are reasons why Nepal has such a relatively high accident rate. Many of those are because of the challenges of operating in mountain airfields that surround Nepal," said Mr Blackie, who was part of a team that probed a 2016 crash of a small turboprop plane in Nepal.
But experts say the Canadian-made Bombardier Dash 8 Q400 is a manoeuverable plane that was developed to fly in Canada's harsh arctic north and should be at home in Nepal's mountainous terrain.
Bangladeshi media said a plane carrying relatives of the dead and injured had left Dhaka airport early Tuesday for Kathmandu.
