The Australian Transport Safety Bureau (ATSB) is investigating an incident where two Qantas Airways A330s came within close proximity of each other, triggering one jet's traffic collision avoidance system (TCAS) on 20 September.
Aircraft VH-EBO was operating a Sydney-Perth flight while aircraft VH-EBS, was on the Perth-Sydney route when the incident happened near Adelaide at 12:13 local time.
Referring to it as a "loss of separation" incident, ATSB says EBS was cruising at 39,000ft (11,900m) when the flight crew of EBO were cleared by Air Traffic Control (ATC) to climb from 38,000ft to 40,000ft and had commenced the climb.
The controller soon cancelled the clearance, leading EBO to descend to 38,000ft. The proximity of the two aircraft, however, triggered an alert from EBS' TCAS.
Qantas says indications are that the loss of separation occurred when one of the aircraft received clearance to climb from the ATC.
"Our pilots followed standard operating procedures in re-establishing the required separation distance following the alert from the onboard notification system," says the airline. "There was no impact to passengers."
ATSB says it will review and analyse the recorded radar and audio data, and look at the relevant ATC procedures, documentation and training. It will also interview both the air traffic controllers and flight crew.
The investigation is expected to be completed by September 2014.