The US Bangla plane after the crash with rescue workers scouring the wreckage at Kathmandu airport. Photo: Reuters/Navesh Chitrakar

A flurry of reasons has been given as possible causes for the crash of a US-Bangla plane at Kathmandu airport on Monday – ranging from pilot fatigue to confused communication with air-traffic controllers about which end of the runway the flight would land.

Speculation over reasons for the crash, which killed 51 of the 67 passengers and four crew on board, has run rife after a tape of the radio conversation between the captain of the flight, Abid Sultan, and officials at Tribhuvan International Airport in Nepal was uploaded to YouTube.

The ill-fated plane was a Bombardier Dash-8 Q400 – a twin-engine turboprop used for short to medium-range flights of 500 miles or less. US-Bangla was the fourth owner of the 17-year-old aircraft, after Royal Jordanian, Augsburg/Lufthansa Regional and Scandinavian airlines.

Flight BS-211 crash-landed at Kathmandu at 2.18pm local time after a 75-minute trip from the Bangladeshi capital Dhaka. A total of 51 people — 28 Bangladeshis, 22 Nepalese and a Chinese national — have died so far, including the four Bangladeshi crew members.

The flight data recorder was recovered on Tuesday and a six-member team from the Civil Aviation Authority of Nepal has launched a formal inquiry.

Aviation experts say a definitive cause of the accident cannot be pinpointed without a thorough investigation. However, the leaked conversation between the pilot and air-traffic controller (ATC) has spurred great debate and buck-passing over who was most to blame.

What was in the leaked conversation?

The leaked conversation between the pilot Sultan and an air-traffic controller reveals moments of confusion over which end of the runway the plane should land from after it circled the airport twice.

Tribhuvan has a single 10,007-feet (3,050-metre) concrete runway orientated 02/20. There is no instrument landing system, which enables pilots to conduct a predetermined maneuver landing if they are unable to see the actual runway.

The conversation shows that the ATC told the pilot not to proceed towards runway 20 at the northern end and hold onto its current position. The captain agreed and said he would orbit in the air. But a moment later, the tower cleared the plane for landing and asked if the pilot wanted to land from 02 – the southern end instead.

The captain said he would land from 20, the northern end. The ATC then asked if he had the runway in sight. Captain Sultan, who tried doing a visual landing, replied “Negative.”

The tower then instructed him to maneuver to the right. Sultan did that and a few moments later said, “Affirmative”, which meant he then had the runway in view. The tower then gave him a clearance.

But, even though pilot Sultan had sought permission to land from the northern end (20), the next thing he said was, “Cleared to land on runway 02.” And the ATC seemed to clear him to land from the southern end of the runway. The pilot’s last recorded words were “Sir, are we cleared to land?”

After some silence, the seemingly alarmed air-traffic controller shouts, “I say again, turn!” There is further silence, then the tower calls out ‘Fire One’, indicating that a crash has occurred.

Blame game

After the crash, Kathmandu airport general manager Rajkumar Chetri told the media in Nepal that the aircraft skidded off the runway after trying to land in the “wrong direction against the order of the control room”.

Chetri said the control room had given permission for a landing from the southern end – but it landed from the northern end after making two rounds in the sky.

And the plane was not properly aligned for landing, he said. “When the air-traffic controller was informed about the alignment, there was no response. And then the plane descended from close to the airport tower towards the right side (near army hangar).”

But US-Bangla CEO Imran Asif later told the media in Bangladesh that after, listening to the leaked conversation, he suspected “negligence” on the part of the air-traffic controller for not giving clear information. He claimed there was a tendency for pilots to be given wrong information at Tribhuvan Airport.

“Our pilots were given different information at different times. And we think that this accident took place due to this miscommunication. The negligence was not from our part, it was from the Air Traffic Control tower,” Asif claimed.

Pilot’s fifth flight of the day

Asia Times spoke with a number of pilots in Dhaka who have years of experience flying the Dhaka-Kathmandu route. They did not want to be quoted on the record as aviation officials have prohibited them from speaking about the incident while it is “still under investigation.”

One senior pilot who has flown the Dhaka-Kathmandu route for decades said he had detected a “severe cockpit error” after listening to the radio conversation.

Under standard aviation norms for Kathmandu — which is a special airport because it is surrounded by mountains — the co-pilot should communicate with the control tower while the main pilot maneuvers the plane for landing or take-off because the routes for arrival and departure are classed as “difficult terrain”.

But the audio posted on YouTube revealed that Sultan, the senior pilot had done both the flying and communication, which should have been done by the co-pilot, Prithula Rashid.

“It seemed he [Sultan] was manoeuvring the plane and talking to the tower at the same time, which made him lose concentration and [he] eventually lost sight of the runway while switching from runway 20 to runway 02,” the senior pilot said, adding that it was vital to keep the runway at Tribhuvan in sight all the time.

Meanwhile, Asia Times learnt that it was Captain Sultan’s fifth flight on that day. Before the Dhaka-Kathmandu flight, Sultan had flown two flights from Dhaka to Chittagong and back on the day within a gap of five hours.

Kamrul Islam, US-Bangla general manager and spokesperson, admitted this but told Asia Times that US-Bangla pilots had no problem taking such workload.

“Dhaka-Chittagong-Dhaka is a 45-50 minute flight in both ways and Dhaka-Kathmandu-Dhaka is 1-1.15 hours both ways. So making three such [return] flights on a day is not abnormal,” he said.

Experienced pilot but was he tired?

Islam said that Sultan, a former Bangladeshi Air Force pilot, had landed at Kathmandu more than 100 times and was specially trained to land at that airport. “He had more than 5,000 hours of flying experience,” he added.

Meanwhile, a pilot with a foreign airline in Dhaka told Asia Times it seemed from the conversation that the pilot Sultan was fatigued. He said it was one thing to fly a plane for 15-16 hours and another thing to do multiple landings and take-offs on a single day.

Air Vice Marshal M Naim Hassan, chairman of the Civil Aviation Authorities of Bangladesh (CAAB), told Asia Times that the authority would go through the pilot Sultan’s personal logbook, to see if he was engaged in flying extra hours in violation of International Civil Aviation Organization (ICAO) rules.

According to ICAO rules, he said, a pilot can fly 90 to 100 hours per month. “We will check whether he had crossed the limit.”

Meanwhile, another senior pilot with state-owned Biman Bangladesh Airlines told Asia Times the ATC initially cleared a landing on the Kathmandu runway from the southern end, but when the plane started descending the ATC, suddenly gave an order for the pilot to hold.

As far as he understood, the flight had already descended to a level at which proper maneuvering in the thin air pressure of Kathmandu — which is at an elevation of 4,500 feet — is quite difficult. “The ATC can’t evade the blame,” the pilot said.

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