What happened
During the execution of the DEENA SEVEN standard instrument departure (SID), a loss of separation occurred between two heavy aircraft. The lead aircraft, a Boeing 787, was followed by an Airbus A330. The air traffic controller assessed that both aircraft would exhibit similar climb performance and cleared them to the same altitude in sequence. However, because the Airbus A330 was operating a domestic flight, it carried a significantly lower fuel load compared to the heavily loaded international Boeing 787, resulting in superior climb performance. As the Airbus A330 climbed more effectively than anticipated, the separation between the two aircraft reduced. The controller, who had become distracted by planning separation for other traffic, did not immediately detect the closing distance. Upon noticing the reduction in separation, the controller instructed both flight crews to take action to increase the distance between the aircraft.
The investigation
The investigation examined the controller's assessment of the aircraft's climb capabilities and the structural design of the departure procedure. It was found that the controller incorrectly assumed the two aircraft would perform similarly, failing to account for the impact of differing fuel loads on climb rates. Furthermore, the investigation noted that while the controller suspected a loss of separation, they did not issue a specific safety alert or clarify that the instructions provided were intended as an avoiding maneuver. It was also noted that a short-term conflict alert (STCA) warning likely did not trigger during the event.
Additionally, the investigation scrutinized the DEENA SEVEN SID itself. While SIDs are designed to manage traffic efficiently, this specific procedure lacked a built-in method for ensuring lateral separation for departing aircraft with varying climb profiles. Because the procedure required aircraft to meet two distinct conditions before turning, there was no guarantee that the aircraft would turn at the same distance from the airport. Airservices Australia has since advised that the DEENA SEVEN SID has been redesigned to remove these conditional requirements to prevent such occurrences.