Australia's transport safety authority is probing whether a trainee air traffic controller is to blame after two Qantas planes came "very close" to each other in the skies above Sydney.
The incident — which occurred last August — was so serious, one of the aircraft's emergency collision avoidance systems was activated.
Details of the near-miss are contained in a preliminary report by the Australian Transport Safety Bureau (ATSB), which was yesterday released and categorised the incident as "serious".
It happened after an Airbus A330 was cleared to take off from Sydney Airport at the same time a Boeing 737 was about to land.
The A330 travelled just 152 metres below the 737 aircraft in a tense few seconds described as "very close" by the plane's captain, who radioed the control tower straight away.
They were separated by a lateral distance of 796m.
The ATSB's report found the "loss of separation" between the planes occurred when both aircraft turned to the right after the 737 was told to do so by the trainee air traffic controller following a missed approach procedure.
The aircraft's airborne collision avoidance system — a last-resort safety mechanism — was activated as a result.
Both planes ascended after the close shave, with the A330 climbing 1,500m and continuing to Melbourne, while the 737 went about 900m higher before landing safely.
The trainee was working supervised in the tower, the report found.
They had worked as an air controller at other airports and were training to take up the position at Sydney Airport.
In a statement, Qantas said: "Even if both aircraft stayed on the same flight paths, they were not in danger of colliding.
"We're continuing to work with the ATSB on their ongoing investigation."
Dr Stuart Godley, the ATSB's Director of Transport Safety, said the investigation would now probe the planes' instruments as well as air traffic control procedures, controller training and flight data.
