The Australian Advanced Air Traffic Control System (TAAATS) held two flight data records for VH-HYY, one from Melbourne to Adelaide and the other from Melbourne to Sydney. The crew were cleared to Adelaide but the Sydney flight data record was coordinated in TAAATS. After the aircraft departed, the controller saw that its radar track did not "couple" with the flight data record. This was achieved when the air traffic system linked an aircraft's secondary surveillance radar track with the flight data record assigned to that code. Separation standards were not infringed.
Airservices Australia found that, in anticipation of a busy departure period, the controller operating the combined surface movement control and airways clearance delivery positions noted clearance details on all pending flight progress strips. The controller cleared the crew of HYY for Adelaide and ticked the clearance and altitude annotations on the strip after receiving a correct read-back. This was required to confirm that the clearance had been issued and read back correctly. After the surface movement control and airways clearance delivery positions were individually activated, and during handover/takeover, the Adelaide strip for HYY was accidentally placed on the airways clearance delivery console and the Sydney strip placed on the surface movement control console. When the crew sought a taxi clearance, the surface movement controller did not notice that the clearance annotated on the Sydney strip was unticked but still activated the strip. The strip was then passed to the coordinator position and the controller there changed the state of the HYY flight data record in preparation for the aircraft's departure. The coordinator processed the first observed record for that aircraft and did not notice that the clearance had not been ticked. The departure controller then received a system "preactive" electronic strip showing that HYY was taxiing for a departure to Sydney. The strip in the tower was then passed to the aerodrome control position. Neither of the two controllers staffing that position noticed that the clearance on the HYY strip had not been ticked. Controllers at each operating position were required to maintain and arrange their strips.
Because TAAATS gave a separate secondary surveillance radar code to each flight data record in the system, the Adelaide and Sydney flight data records for HYY had different codes. The HYY crew were later cleared for take-off and after departure, the Sydney flight data record did not link to the aircraft's radar track. After confirming that the aircraft track displayed on the radar was that of HYY, the departure controller told the crew to select the aircraft's transponder on the secondary surveillance radar code assigned to the Sydney flight data record. The track then linked to the flight data record and the electronic strip on the departure controller's display changed to active. Shortly after, the departure controller gave an amended clearance to the crew of HYY for direct tracking to Sydney. The crew replied that the flight was to Adelaide.
The Aeronautical Information Publication AIP GEN 3.4-36-38 gives the radiotelephony phraseology required around an aerodrome. When pilots seek a clearance and clearance delivery is in operation, they must provide the aircraft's flight number and the aerodrome where they first plan to land. When they seek a clearance to taxi, they may include this aerodrome if they wish. The automatic voice recording confirmed that the HYY crew had supplied their destination when seeking a clearance but that they did not include it when asking for a taxi clearance. In other words, they had complied with the AIP radiotelephony phraseology procedures.