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A misinterpreted instruction from air traffic control contributed to a separation incident between two Qantas 737-800s at Sydney Airport in April last year, the ATSB has found.
In its report, the transport safety watchdog notes that on 29 April 2023, VH-VZM was cleared to take off for Brisbane on Sydney’s parallel runway 16L at the same time as VH-VZW, arriving from Queenstown, was landing, each with around 170 passengers on board.
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Air traffic controllers observed that VH-VZW was too close to ensure proper runway separation; however, the instruction for a go-around was delayed by around 12 seconds due to “an inadvertent interjection by the tower shift manager”.
Shortly after the go-around, the controller then instructed VH-VZW to turn left off the runway heading after reaching 2,100ft altitude.
“The flight crew of the second aircraft [VH-VZW], at this time of high workload, misinterpreted this instruction as overriding the published missed approach procedure, which calls for a left turn at 600 ft,” ATSB director transport safety Dr Stuart Godley said.
Due to misinterpreting the controller’s instruction, the crew of the second aircraft maintained the runway heading as they climbed through 600ft and, as the two aircraft climbed away from the runway, separation reduced to a minimum of 1.5km laterally and 330ft vertically.
The controller had both aircraft in sight throughout the occurrence, and the ATSB assessed that adequate visual separation had been maintained.
In response to the incident, the air traffic services provider, Airservices Australia, advised the ATSB that it had undertaken and would undertake a range of safety actions.
“These include a detailed analysis of landing runway occupancy times at Sydney, and possibly other major airports, to determine expected runway occupancy times for different types of aircraft and conditions,” Dr Godley noted.
Further actions, detailed in the final report, include adding defensive controlling techniques and minimum assignable altitudes for go-around scenarios, conducting an assurance review of go-arounds at Sydney involving a second aircraft requiring controller intervention, and adding night-time go-around scenarios to compromised separation training.
“In complex airspace settings, it is inevitable errors will sometimes be made by controllers and pilots alike,” Dr Godley said.
“Consequently, the system within which these activities take place should be designed to be resilient to error and to reduce the impact that individual actions can have on the overall safety of operations.”
