Nepalese investigators have retrieved the black box from the wreckage a Bangladeshi plane that crashed here, killing 49 people, authorities said today as the conversation between the air traffic controllers and the pilot before the tragedy indicated a possible confusion over the runway.

The Dhaka to Kathmandu US-Bangla Airlines flight, with 67 passengers and four crew members on board, caught fire after it careened off the runway and ploughed into a football ground near the Tribhuvan International Airport yesterday.

“The flight data recorder has been recovered we have kept it safely,” said Raj Kumar Chettri, the airport’s general manager, adding that an investigation into the cause of the crash had begun.

The airline and airport authorities have blamed each other for the tragedy, the worst in the country in 25 years, after it emerged that there was confusion over landing instructions.

There were 33 Nepalese nationals on board flight UBG 211, a Bombardier Dash 8 Q400. Others include 32 Bangladeshis, one Chinese and one Maldivian.

Bombardier is a twin-engine, medium-range and turboprop aircraft.

Canadian plane maker Bombardier said it was sending an air safety investigator to the site, as well as a field service representative.

The Nepal government formed a six-member committee to probe the crash-landing.

A high-level team led by Bangladesh’s Minister of Civil Aviation and Tourism M K M Sahajahan Kamal is scheduled to arrive in Kathmandu today.

The last four minutes of the conversation between the pilot and Air Traffic Control at the airport indicates a possible confusion in the mind of the pilot about Runway 02 (the southern end) and Runway 20 (the northern end), a Nepalese newspaper reported.

The Nepali pilots of other aircraft are heard warning the ATC that the US-Bangla pilot seems disoriented, according to the Nepali Times.

At the very outset of the tape, the control tower was heard warning the pilot, “I say again, do not proceed towards Runway 20.” And later, he is warned to remain on hold and not to land because there is another aircraft on approach.

After the plane apparently takes a right orbit, the ATC asks the pilot whether he wants to land on Runway 02 or 20.

The latter responds and says “We would like to land on 20”; he is cleared to land on that end of the runway, the report said.

The pilot was then asked if he has the runway in sight, to which he replies, ‘Negative’, it said.

He was asked to turn right, but immediately after that, the Flight 211 pilot says “Affirmative”, that the runway is in sight.

The pilot then says, “Cleared to land Runaway 02”, even though he had sought permission for 20. However, ATC too now clears him to land on Runway 02.

Meanwhile, speaking to the Army 53 aircraft which is on hold about 10 kilometres away, the ATC says the Bangladesh aircraft is “on final for 20”.

The last recorded words of the pilot are: “[Unintelligible] said sir, are we cleared to land?” After some silence, the clearly alarmed ATC controller shouts, “I say again, turn !”.

There is silence for a while, then a ‘Fire One’ calls the tower, indicating that a crash has occurred and the airport fire tender has been activated.

The Dhaka-based US-Bangla Airlines is a private carrier that launched in July 2014 with the motto “Fly Fast Fly Safe”. The airlines is a unit of the US-Bangla Group, a US Bangladeshi joint venture company.

Nepal has witnessed a number of accidents involving aircraft in recent years.

Yesterday’s accident is deadliest since September 1992 when all 167 people aboard a Pakistan International Airlines (PIA) plane were killed when it crashed near the Kathmandu airport.

In February, 2016, Tara Air’s Twin Otter 400 crashed in Rupse of Myagdi, killing 23 people.