de Havilland Canada DHC-8-202, VH-TQX

On 19 April 2005 at about 1522 Eastern Standard Time, a Boeing Company 747-422 (747) aircraft was en route from Sydney, NSW, to Los Angeles, USA, on climb to flight level (FL) 310 and a de Havilland Dash 8 (Dash) aircraft was en route from Lord Howe Island to Sydney, maintaining FL240. The crew of the Dash had been issued with a clearance to descend to 10,000 ft above mean sea level. The intended tracks of the aircraft intersected at a point about 90 NM east of Sydney.

The aircraft were under radar control by the Brisbane Centre Ocean sector controller. The Australian Advanced Air Traffic System (TAAATS) assessed the two aircraft as potentially being in conflict and activated the short-term conflict alert (STCA) on the air situation display. Following activation of the STCA, the Ocean controller saw that the aircraft were about 16 NM apart and instructed both crews to turn their respective aircraft left in an endeavour to maintain the minimum radar separation standard of 5 NM. Analysis of recorded data from TAAATS showed that the aircraft passed with 4.1 NM lateral and 400 ft vertical spacing. The required minimum vertical separation standard was 1,000 ft. There was an infringement of separation standards.

The controller had been operating in the position for about 50 minutes prior to the occurrence. The level of complexity within the sector was reported to be light to moderate. The controller reported that despite reviewing the aircraft's tracks he expected the track of the 747 to be northwest of the inbound track of the Dash 8. Immediately prior to the activation of the STCA the controller was not monitoring the aircraft situation display as he was discussing operational coordination issues with an operational supervisor, who was consulting a chart located near the Ocean sector console position. The controller had initiated the discussion with the supervisor to follow up previous correspondence on the issue.

A review of breakdown of separation occurrences, conducted by Airservices Australia in June 2003, found that 92 percent of en route sector infringements of separation standards involved an error in either building or maintaining situational awareness by the controllers involved. The review made 31 recommendations and Airservices Australia has implemented all the recommendations of the review.

Since July 2003, the controller had undergone refresher training that included compromised separation (February 2004), separation assurance (February 2004), human factors awareness (March 2005) and situational awareness (March 2005).

In this occurrence, the controller did not perceive the potential conflict between the aircraft, despite previous refresher training that should have assisted in the task.

Although the presence of the supervisor in the operations room created an opportunity to discuss an operational issue, it was not a priority. The controller should have discussed the issue at some other time when he was not responsible for an operational position. The supervisor was also in a position to defer the discussion with the controller, until a more suitable time or location, which would have reduced the likelihood of compromising operations.

While distraction could not be discounted as a contributing factor, the circumstances of the occurrence are consistent with the findings of the Airservices Australia June 2003 review, particularly with respect to low levels of situational awareness by controllers. Over time, the benefits of the implementation of the review recommendations in helping to develop controller awareness of potential performance limitations should become apparent.

Airservices Australia safety action

The post implementation review by Airservices Australia of the June 2003 review of breakdown of separation occurrences found that since the recommendations were implemented, errors in either building or maintaining situational awareness by the controllers involved had reduced to 44 percent of occurrences involving infringements of separation standards.