Airservices Australia will add a new risk assessment to its training procedures for enroute air traffic controllers following an investigation into a loss of separation incident that occurred in Australia in 2011.
The incident occurred on 29 July 2011 and involved two Boeing 737-800s, one registered VH-VZC and operated by Qantas Airways and the other registered as VH-VOT and operated by Virgin Australia.
According to the Australian Transport Safety Bureau (ATSB) report, the two aircraft were being sequenced to land at Brisbane and as a result of delays, had been instructed to hold at an instrument flying rules holding point 93km (50nm) south-south-east of the airport.
At that point, both aircraft had been sequenced by an enroute air traffic controller in the Inverell sector, but were handed over to another controller in the adjoining Gold Coast (GOL) airspace sector.
At 07:52 local time, the GOL controller assigned the Virgin aircraft to descend to 27,000ft (8,200m), which resulted in a loss of separation assurance between it and the Qantas aircraft, which at the time was at 28,000ft and 5.8nm behind it.
The controller subsequently issued another instruction to VH-VOT to descend to 17,000ft, at which point it was 4.4nm ahead and 1,900ft above the Qantas aircraft. The controller also continued to control other aircraft in the sector at the time.
At 07:56, separation was lost when the two aircraft came within 4.1nm and 900ft vertical as VH-VOT descended through 28,900ft. The required separation minimum was 5nm by radar when there is less than 1,000ft vertical separation.
The crew operating the Qantas 737 requested information about the other aircraft from the controller after the aircraft's traffic alert and collision avoidance system identified the other aircraft.
The controller then identified that there had been a loss of separation, and instructed the Qantas aircraft to turn right and then changed that to direct it to descend to 25,000ft. The controller also instructed VOT to maintain altitude at 28,500ft.
The controller then provided the Qantas crew with a traffic alert informing them of the Virgin aircraft's relative position, and instructed them to descend to 27,000ft before amending the clearance to 25,000ft. As a result, the separation was re-established at 07:58.
During the action to re-establish separation between the two aircraft, they came within 3.9nm and 400ft vertical distance of each other.
The ATSB investigation into the incident found that while the GOL controller had 10 years of experience in both tower and enroute air traffic control, he had received only four weeks of on-the-job training to handle the GOL sector instead of the usual six weeks.
It was also found that the controller had not completed compromised separation recovery training.
The ATSB identified that Airservices Australia did not have a requirement for a systematic risk assessment to be conducted and documented when reducing the amount of training a controller receives. It categorised this as a significant safety issue.
As a result of the investigation, Airservices Australia will "develop a training variation form 'to systematically assess risk associated with amendments to the planned length of controller training programmes.'"
"The ATSB is satisfied that this safety action will, when implemented, satisfactorily address the safety issue," it says.