Incident Overview
Radar data indicated that as QF652 and QF601 passed each other, QF652 was at 9,000 ft and QF601 at 8,000 ft, with 2.3 NM lateral separation. Further radar data showed QF652 at 8,700 ft and lateral separation of 2.6 NM. The required separation was 3 NM or 1,000 ft; the minimum recorded was 2.5 NM and 700 ft. The incorrect descent clearance given to QF652, intended for QF62, caused this loss of separation.
Controller Comments
The approach controller had been on duty since 0200 and reported feeling alert and well rested, noting that operations were progressing smoothly prior to the incident. The controller commented that between 0500 and 0600 the workload typically increases due to conflicts between departures and arrivals, but assessed their workload at the time as moderate. The controller acknowledged that techniques for handling similar call signs—such as appending 'heavy' or the aircraft's position—were not employed in this instance, though both aircraft were 'heavy,' making that distinction moot. After the clearance was inadvertently read to QF652, both aircraft descended. When the flight crew read back 'Qantas six fifty two,' the controller did not identify the mismatch with the aircraft label, possibly because it was the expected response.
Procedures and Initiatives
The Australian Aeronautical Information Publication (AIP) General 3.4 paragraph 4.17 specifies that flight numbers should consider those already in use by the operator and other agencies. The Manual of Air Traffic Services (MATS) 6.2.1.1 outlines actions to mitigate call sign confusion, such as emphasizing numbers, repeating call signs, or advising pilots of similar call signs.
Airservices Australia had established a process to monitor call sign confusion in the Brisbane area after receiving multiple confidential reports. This process involved reviewing occurrences and notifying airlines. A monthly 'call-sign conflict report' was distributed to domestic operators until 2016, when distribution was paused for a system upgrade. The report distribution has since been reinstated using the previous system while improvements continue. Airservices noted that existing procedures in the AIP and MATS, as well as the use of 'group format' for transmitting call signs, aim to reduce confusion.