Investigators in Myanmar have disclosed that they were not informed about an air traffic control mix-up, which led to a serious landing incident at Yangon, until nearly two weeks after it occurred.
The incident, on 18 December last year, involved a Thai Smile Airbus A320 which had initially been instructed to line up and wait on runway 21.
But almost 2min later, after the A320 was already in position, the air traffic controller told its crew to "line up and wait behind" another aircraft – an ATR 72-600 of Mann Yadanarpon Airlines – which was on short final.
Myanmar's aircraft accident investigation bureau says the controller "forgot" the line-up clearance she had previously given to the A320.
The A320's crew contacted the tower three times in the space of 20s to inform that they were already occupying the runway, without response.
"When the [A320] replied that it was on the runway, and lined up [waiting] for take-off clearance, [the controller] did not know what to do," says the inquiry.
Nearly 15s after the third call from the A320, an approach controller stepped in and cleared the flight for take-off. The controller also told the ATR to continue its approach.
Radar evidence, says the inquiry, shows the ATR crossed the threshold before the A320 had cleared the runway.
"That was contrary to the control of arriving aircraft [regulations]," it adds, although the longitudinal separation between the ATR and A320 was around 1.2nm. The ATR crew was "not aware" of the incident, says the inquiry.
Any occurrence involving a runway incursion or obstruction needs to be detailed in an air traffic incident report, it states.
But air traffic control "did not inform" the accident investigation bureau of the incident, and the bureau says it only learned of the event 11 days later, on 29 December.