Extraordinary air traffic control communications with a US-Bangla Bombardier Q400 shortly before it crashed at Kathmandu reveal confusion over the runway to which the aircraft had been cleared.
Kathmandu has a single runway with the designation 02/20.
The Q400 had initially been cleared to land on runway 02, and advised of a 7kt wind from 220° – resulting in a 6kt tailwind component.
But the Kathmandu controller queried the crew shortly afterwards, stating: "You were given landing clearance to runway 02. You are going towards runway 20."
The aircraft, operating flight BS211, is then cleared by a separate controller to land on runway 20.
About a minute later another aircraft on approach questions the runway in use, and the tower calls the Q400 to request the crew's intention, to which the pilot appears to confirm a landing on runway 02.
The mix-up persists as the controller initially instructs a right downwind pattern for runway 20, before correcting to a right downwind for runway 02, and clearing the other approaching aircraft to land on 02.
After the tower informs the Q400 crew to be aware of the landing aircraft, the Q400 pilot says he will be approaching runway 02 – prompting a response from the controller, asking the pilot to confirm he is tracking towards runway 20.
When the pilot responds "affirmative", the controller – with urgency evident in his voice – instructs him again to join the right downwind for runway 02, and warns of the other aircraft on final approach. This other aircraft again requests confirmation of, and is granted, landing clearance for 02.
"I say again, do not proceed towards runway 20," the controller urges the Q400 pilot, who responds by saying he will execute a right-hand orbit to hold for runway 02.
"OK, that's good, but do not land," the controller adds.
Around a minute later the controller offers the Q400 either runway, to which the pilot replies that he would like runway 20.
The controller gives the Q400 landing clearance for 20, advising of wind from 270° at 6kt, and the pilot confirms he is cleared to land.
When the controller subsequently asks whether the pilot has the runway in sight, and is told "negative", he tells the aircraft to turn right and asks for confirmation that the runway is still not in sight.
But the pilot immediately responds with a request for landing clearance, which the controller grants, initially without mentioning the runway designation.
The pilot reads back the landing clearance, but mentions runway 02, rather than 20, and the controller simply confirms: "Roger, runway 02, cleared to land."
Transmissions between the aircraft and Kathmandu controllers were obtained through the LiveATC archive.
Some 20 occupants are reported by local media to have survived the accident, but official figures on the situation have yet to be released.