What happened

On 18 January 2012at 2125 Eastern Daylight-saving Time, there was a loss of separation (LOS) between an Airbus A320, registered 9V-TAZ, and an Airbus A340, registered A6-EHH, 907 km NW of Karratha, Western Australia. The aircraft were under the air traffic control of Airservices Australia. The A320 was southbound at FL 350 and the A340 was heading west and cleared to operate in a ‘block’ level, anywhere between FL 340 and FL 360. The aircraft were estimated to cross waypoint TANEM within 2 minutes of each other. The relevant separation standards were 1,000 ft vertical separation or 15 minutes lateral separation at the same position. Controller 1, who approved the block level clearance, did not detect the traffic confliction prior to handing over to controller 2. After a short break, controller 2 handed back to controller 1, and the confliction was detected by controller 2 during the handover. Compromised separation recovery techniques were applied to re-establish vertical separation.

What the ATSB found

The two controllers were experiencing a high workload due to a range of factors, including traffic levels, weather diversions and the airspace configuration, and controller 1 had limited opportunity to consolidate their training and skills before being rostered onto more complex sectors and situations. The ATSB found that Airservices’ processes for monitoring and managing controller workloads did not ensure that newly-endorsed controllers had sufficient skills and techniques to manage the high workload situations to which they were exposed. In addition, Airservices had limited formal guidance regarding how to determine appropriate consolidation periods for en route controllers on one sector before they were transitioned to commence training on another sector. Further safety issues were also identified relating to the application of block level clearances, and the continuing absence of an automated air traffic conflict detection system available for conflictions involving aircraft that were not subject to radar or ADS-B surveillance services.

What's been done as a result

Airservices reported that changes had been made to the configuration, training and rostering arrangements for the airspace sectors involved in the occurrence. The commissioning of a radar in northern West Australia had reportedly alleviated controller workload in two of the airspace sectors, with enhanced surveillance of the majority of aircraft operating in that airspace expected with the mandate of automatic dependant surveillance- broadcast (ADS-B) effective in December 2013. A working group had also been established to determine a suitable workload model to monitor and forecast controller workload on a sector by sector basis. In addition, the first stage of a flight plan conflict function had also been deployed in Brisbane Upper Airspace, with further roll out planned in Melbourne Centre in 2014. The ATSB is not satisfied that Airservices has adequately addressed the identified safety issues regarding formal guidance for consolidation periods for newly-endorsed controllers and the limited formal guidance to controllers and pilots regarding the conditions in which it was safe and appropriate to use block levels. As a result the ATSB has made formal recommendations to Airservices.

Safety message

Ideally the best way of managing workload is to reduce the level of work demands and distractions. If the work demands cannot be reduced, then another option is to ensure the controllers have the experience, skills and techniques to effectively manage their task demands. Overall, high workload can have significant effects on a controller’s performance, and it needs to be monitored and managed using a systemic approach, particularly for less experienced controllers but also controllers who have recently received a new endorsement. The instances of other recent loss of separation occurrences involving high workloads and newly-endorsed controllers on other sector indicates that this problem was not restricted to the sectors involved in this occurrence.