The Australian Transport Safety Bureau (ATSB) has stressed the importance of “clear communication and coordination” between different air traffic control systems operating in unlinked, but adjacent airspace.
It made the point in the release of the final investigation report into a loss of separation involving two Boeing 737-800s near Brisbane Airport.
One reason the incident occurred was a lack of communication between the two adjacent airspaces — one belonging to the airport, and the other controlled by the military, the bureau found.
The incident took place in the afternoon of 11 October 2018. At the time, a Qantas 737-800, registered VH-VZD, was arriving from Melbourne and on approach to Brisbane Airport. A Virgin Australia 737-800, registered VH-YFW, had just departed from Brisbane, heading to Proserpine in Queensland.
The Qantas 737 had passed through airspace controlled by the Royal Australian Air Force (RAAF) into Brisbane airport airspace.
At the time, weather warnings were in place at both Brisbane and RAAF Amberley airports, warning of approaching inclement weather from the west.
The Virgin Australia aircraft had departed Runway 19 at Brisbane and had turned right to head 230°. The flight crew advised Brisbane’s air traffic controllers that they were unable to make any more right turns due to the weather conditions.
The Brisbane departures controller provided his counterparts in Amberley with the identification of the aircraft.
Amberley controllers, meanwhile, advised Brisbane that the Qantas aircraft was on approach at a similar flight path, to which Brisbane controllers said the Virgin Australia aircraft was to turn right.
Brisbane controllers asked the Virgin Australia aircraft to advise when they would turn northwards, but the latter replied that they will be staying on course for some distance due to the weather situation. It was around then that the aircraft entered the Amberley airspace.
Amberley controllers attempted to contact the Brisbane departure controller to inform them of the incoming arrival of the Qantas aircraft. It was only after 17 seconds that it managed to establish contact.
At the time, both aircraft were on different radio frequencies — the Qantas jet on Amberley approach frequency, and the Virgin Australia aircraft on Brisbane departures frequency.
Both parties then executed separation recovery, with the Amberley controllers alerting the Qantas jet to turn northwards to the left. It also established contact with the Virgin Australia jet, and advised it to turn southwards to the left.
The ATSB says that both the Amberley and Brisbane air traffic controls were “non-linked air traffic management systems, which did not share a common display”. This therefore necessitated manual coordination between both parties.
It found that the Virgin Australia aircraft entered Amberley airspace “without a hand-off” from Brisbane, and without instructions to the flight crew to change to Amberley frequency.
“This resulted in [the flight crew] monitoring an incorrect frequency on entry to Amberley airspace and Amberley ATC initially unable to communicate with the flight crew,” the ATSB notes.
It was this lack of proper communication between both parties that “delayed the opportunity for Amberley ATC to resolve the impending conflict”.
Calculations indicate that the 17-second delay "led to a reduction in the lateral separation of the two aircraft by approximately 6 km". The ATSB report did not state how close the two narrowbodies were during the incident.
“Air traffic controllers need to maintain a clear understanding of responsibility for separation assurance, especially when operating without a shared traffic picture,” the ATSB says in its safety message.
To this end, both Brisbane air traffic control and Amberley have taken corrective actions to improve communication. Among steps taken is the deployment of a dedicated communications channel between Amberley approach and Brisbane departures south air traffic control positions.
Cirium fleets data shows that VH-VZD was delivered to Qantas in 2008, while Virgin Australia took delivery of VH-YFW in 2016.