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Circumstances The Arrivals North Controller [ARRN] had commenced duty at approximately 0705 EST and was experiencing a period of heavy air traffic. He had requested the previous occupant of the position to remain at the console in the monitor position to assist him in a settling-in period. This controller was in the monitor position during the events of this occurrence. The FLOW controller had decided that he would request the use of Sector 8 airspace for three aircraft to reduce the workload on the arrivals controller and reduce the delay to the aircraft. The Sector 8 controller agreed to the request and raised the required flight progress strips [FPS] for his own reference. After receiving instructions from the FLOW controller to track both VH-TQO and VH-TQQ via Richmond, ARRN proceeded to process the two aircraft onto that track, a track that would take them clear of the main arrival route of Singleton to Sydney. VH-TQO was proceeding at Flight Level [FL]190 on a flight from Tamworth to Sydney. At 0718 ARRN instructed VH-TQO to track direct to Richmond and thence to Sydney. This resulted in the aircraft tracking approximately 210 deg. VH-TQQ was proceeding at FL160 on a flight from Port Macquarie to Sydney and was on a similar track to that of VH-TQO and approximately 12NM behind. At 0721 ARRN instructed VH-TQQ to track direct to Richmond and thence Sydney. This resulted in the aircraft tracking approximately 200 deg. At 0722 ARRN handed to Sector 8 the identification on VH-TQO with the assigned altitude of 8,000ft. This was accepted by Sector 8 who wrote this altitude on the FPS for VH-TQO. Both aircraft were then descended to 8,000ft by ARRN and at 0724 the controller, intending to transfer VH-TQO to Richmond Approach, mistakenly instructed VH-TQQ to contact Richmond Approach [Sector 8]. VH-TAF was on descent to FL200 on a flight from Coolangatta to Sydney and was tracking on the main arrival route from Singleton to Sydney. At 0726 ARRN instructed VH-TAF to descend to 8,000ft. When VH-TQQ contacted Sector 8 the controller acknowledged with the callsign TQQ but notated the details on the FPS for VH-TQO. At 0726 the Sector 8 controller had a departure from Richmond that was conflicting with VH-TQO and elected to vector VH-TQO in order to maintain separation. He issued VH-TQQ, the aircraft on his frequency, with an instruction to turn left heading 140 for separation. The crew obeyed the instruction but were approximately 12 NM north of the point the controller thought the aircraft was passing. The controller saw that VH-TQO was not turning and issued a further left turn to a heading of 120 to VH-TQQ. This placed VH-TQQ on a track that would conflict with VH-TAF. ARRN did not immediately realise that VH-TQQ had turned back towards the main Singleton to Sydney track and it was the arrivals controller in monitor who first saw the new position of VH-TQQ and initiated recovery action. At about the same time the crews of both VH-TQO and VH-TQQ started to question the control instructions and asked if there had been a transposition of the callsigns. At 0728 ARRN instructed VH-TAF to turn left immediately onto a heading of 090 deg. to place that aircraft on a heading away from VH-TQQ. Flight levels were then checked and vertical separation established until radar separation could again be guaranteed.. Radar analysis showed that there was no breakdown in separation as vertical separation existed at all times during which horizontal separation was not provided. The callsigns were very similar and belonged to the same type of aircraft in the same company. Anecdotal evidence and statements from the persons concerned in this occurrence, indicate that this confusion has often arisen because of the common feature of these two aircraft being processed for arrival or departure at similar times. During the course of the interviews five controllers complained of the two callsigns being on frequency together and having had trouble with them at some time or other. The crew of VH-TQQ were expecting to be given the radio frequency change to Richmond Approach at the time the ARRN controller issued the instruction and, therefore, had no reason to query the instruction. The O and Q do not readily stand out from one another on the digital read out of the radar display and this can lead to a confusion of callsigns in high density traffic situations. Significant Factors 1. The callsigns TQO and TQQ are very similar and do not stand out from each other on the digital read out showing on the radar screen. 2. VH-TQO and VH-TQQ were given the same tracking instructions while proceeding 12 NM in trail. 3. Both the Arrivals North controller and the Sector 8 controller used the callsign TQQ when intending their transmissions to be for TQO. Safety Action Since the above incident a further occurrence has been reported to the Bureau. On 23 March 1994 a controller at Sydney transposed the callsigns and issued a clearance to TQO which was intended for TQQ. On this occasion there was no further incident as the pilot queried the callsign immediately and corrective action was taken. Recommendation R930316 With the above occurrences in mind, the Bureau of Air Safety Investigation recommends that Qantas Airways: Change the registration of VH-TQQ to avoid confusion with other callsigns.
 
General details
Date: 31 August 1993 Investigation status: Completed 
Time: 7:20 EST Investigation type: Occurrence Investigation 
 Occurrence type:Loss of separation 
 Occurrence class: Airspace 
Release date: 02 June 1994 Occurrence category: Incident 
Report status: Final  
 
Aircraft 1 details
Aircraft manufacturer: de Havilland Canada 
Aircraft model: DHC-8-102 
Aircraft registration: VH-TQO 
Sector: Turboprop 
Damage to aircraft: Nil 
Departure point:Tamworth NSW
Destination:Sydney NSW
Aircraft 2 details
Aircraft manufacturer: de Havilland Canada 
Aircraft model: DHC-8-102 
Aircraft registration: VH-TQQ 
Sector: Turboprop 
Damage to aircraft: Nil 
Departure point:Port Macquarie NSW
Destination:Sydney NSW
Aircraft 3 details
Aircraft manufacturer: The Boeing Company 
Aircraft model: 737-376 
Aircraft registration: VH-TAF 
Sector: Jet 
Damage to aircraft: Nil 
Departure point:Coolangatta QLD
Destination:Sydney NSW
 
 
 
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Last update 24 July 2015