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The Archer was allowed to depart from Canberra to undertake two training ILS appraches when up to seven Regular Public Transport departures were pending from the reciprocal runway. While the ILS booking system was not intended as a traffic management tool, use of the system for that purpose may have assisted in planning the traffic situation more effectively.

While the Archer was being vectored for the ILS approach, coordination took place between the ADC and the TMA controller for two departures and then, by mutual agreement, for the Archer to conduct the first training ILS approach. The TMA controller was subsequently advised that a further three aircraft were taxiing that had priority and to hold the Archer out. There was no further discussion between the controllers as to when the Archer would be re-sequenced for the ILS approach. From that point in time there was no mutual agreement between the controllers for the use of the reciprocal runway. Moreover, no voice coordination regarding the Archer, as required by local instructions, took place subsequent to the first occasion when mutual agreement had been achieved.

The readback of a callsign as part of the acknowledgment of any coordination is an important defensive measure that helps minimise the likelihood of any misunderstanding between controllers. In this incident, there was no acknowledgment by callsign from the TMA controller during the auto release coordination and the ADC sought notice. Use of the correct acknowledgment and/or a challenge from the ADC to obtain the correct acknowledgment would have likely reiterated that KDQ was in the group of aircraft about to be released, thereby ensuring that the TMA controller had an accurate understanding of the developing traffic situation.

Once the confliction between the two aircraft developed, valuable time was wasted by both controllers discussing the situation, rather than resolving the problem. It was fortunate that the SMC controller had an awareness of the traffic situation and chose to intervene, thereby, prompting action to resolve the confliction before separation standards were infringed.

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