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 takeoff 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.
Although the annotated Adelaide flight progress strip was accidentally placed on the airways clearance delivery console during handover/takeover, there were at least two chances of detecting the error (at the coordinator and aerodrome control positions, for instance) before the aircraft departed. The controllers were supposed to ensure that the flight progress strip annotations reflected the current status of the flight. They should have ticked the clearance to show that it had been issued and read back. Perhaps the controllers assumed the strips were correct because they had been forwarded from at least one other position. Alternatively, the controllers at the positions may have been distracted while managing other aircraft or tasks.
Because air traffic controllers need accurate flight information, they have to continuously assess and confirm data from different sources. Even if crews provide the destination when asking for taxi clearance, mistakes can still happen if controllers do not scrutinise the information.
- The Adelaide flight progress strip in the tower was misplaced on the airways clearance delivery console during the handover/takeover of the surface movement control/airways clearance delivery positions.
- The coordinator did not review the flight progress strip to ensure the crew had been cleared before coordinating the Sydney flight data record for VH-HYY.
- The absence of ticks on the Sydney flight progress strip did not alert controllers to the fact that a clearance may not have been read back or issued.
Local safety action
Airservices Australia's investigation report made five recommendations. As a result, Airservices Australia Southern District issued a request to amend the TAAATS software to:
- Show when there is more than one record in the system for an aircraft during the preactive stage.
- Amend procedures so a clearance is annotated on a flight progress strip only after it is issued.
- Use team training days to brief staff on the importance of ensuring a comprehensive handover/takeover when combining or decombining control positions.
- Reiterate the need for controller vigilance during all operations to ensure that procedural errors are detected and corrected.
- Review staff training in procedures to be adopted when an aircraft's track and its flight data record do not couple.
|Date:||25 October 1999||Investigation status:||Completed|
|Time:||0724 hours EST|
|State:||Victoria||Occurrence type:||ANSP info/procedural error|
|Release date:||27 June 2000||Occurrence category:||Incident|
|Report status:||Final||Highest injury level:||None|
|Aircraft manufacturer||Airbus Industrie|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure point||Melbourne, VIC|
|Departure time||0722 hours EST|