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At 1353 Eastern Standard Time, a Saab 340 departed Sydney for Tamworth climbing to flight level (FL) 140. The flight was conducted within controlled airspace and crossed the boundary between the Sydney and Brisbane Flight Information Regions (FIR), 45 nm north of Sydney. The airline had chosen to use the aircraft registration instead of the flight number as the callsign. This flight stage was one of six separate flight plans held within The Australian Advanced Air Traffic System (TAAATS) for the aircraft. The flight plans had varying departure times, two of which were for Sydney-Tamworth flights. Companies that chose to use flight numbers as the aircraft callsign would have had one unique flight data record for each flight stage held within TAAATS.

TAAATS used a messaging system for flights that cross the FIR boundary, this system used messages called ASIA/PACIFIC ATS Inter-Facility Data Communications (AIDC). The normal AIDC system messaging occurred between the Melbourne and Brisbane Flight Data Processors (FDP). However, as there were several plans in the system for the Saab 340, the Brisbane FDP did not send an accept message (ACP) to the Melbourne FDP. In the absence of an ACP from Brisbane, the Melbourne FDP created an unsuccessful coordination "U" warning in the Sydney controller's label and an aural alarm was generated, indicating that coordination message exchange between Brisbane and Melbourne FDP's was unsuccessful.

The unsuccessful (undeliverable) AIDC coordination messages between the two FDP's were automatically sent to the BN Flight Data Coordinator (TFDC). The Manual of Air Traffic Services (MATS) required that the TFDC print these messages and give them to the controller concerned, however on this occasion the TFDC did not pass on these messages.

The Sydney controller received and acknowledged the "U" warning and alarm. Once the alarm had been acknowledged, the system removed the "U" warning from the screen and the controller then had no visual indication that the aircraft had been the subject of an unsuccessful coordination alarm.

MATS required that aircraft that are subject to a "U" alarm are to be verbally coordinated to the sector in the other FIR. The voice coordination for the Saab 340 did not occur. The alarm was also not mentioned by the Sydney controller during a hand-over to another Sydney controller.

The second Sydney controller initiated the electronic radar hand-off on the Saab 340 to the Brisbane controller. Without waiting for formal acceptance from the Brisbane controller, the Sydney controller instructed the crew to contact Brisbane Air Traffic Control. This was not in accordance with procedures.

The crew of the Saab 340 attempted to contact the Brisbane Maitland (MND) sector controller three times. During the first transmission, the controller was conducting coordination with another unit, and did not hear the aircraft. The second time the crew attempted to contact MND, another pilot over transmitted and the controller did not hear the transmission. The third time, the crew only used the callsign of the aircraft and did not advise their flight level. The controller instructed the crew to "standby".

The MND controller was under training, and had only just returned to controlling duties after a long absence. The MND controller did not call the crew of the Saab 340 back.

As the Brisbane FDP had not processed the flight data record (FDR) for the Saab 340, the aircraft appeared on the MND air situation display (ASD) as a black "unconcerned" track. This track would only have displayed a secondary surveillance radar code and level in the label. It did not display the aircraft's call sign.

When the Saab 340 entered Brisbane's airspace 45 nm north of Sydney, there were numerous other black tracks outside controlled airspace (OCTA) on the MND sector ASD.

At the time the crew of the Saab 340 were attempting to contact the MND controller, the aircraft's label was superimposed on another black track directly underneath it. It is a common occurrence to have aircraft labels overlying each other. TAAATS provides functionality to enable the controllers to move the aircraft labels to reduce label clutter.

The aircraft then passed through Nambucca (NAA) and Armidale (ARM) Sectors, as a black track in controlled airspace, without being detected by the controllers.

Recorded radar data indicated that the Saab 340 did not pass adjacent to any other aircraft and consequently there was no infringement of separation standards. The first time that the Armidale (ARL) sector controller became aware of the aircraft was when the crew of the Saab 340 eventually contacted the MND controller for descent into Tamworth. The aircraft was subsequently radar identified and processed normally into Tamworth.

 

LOCAL SAFETY ACTION

As a result of this occurrence, Airservices Australia has modified the software in TAAATS to improve the way that a flight data record can be selected from the flight plan window where multiple flight data records exist and has improved the AIDC processing by changing the logic used in uniqueness checking. These software modifications were approved for release for operational use in September 2001.

 
General details
Date: 05 July 2000 Investigation status: Completed 
Time: 1403 hours EST  
Location   (show map):56 km S Maitland Investigation type: Occurrence Investigation 
State: New South Wales Occurrence type: Breakdown of co-ordination 
Release date: 24 September 2001 Occurrence class: Airspace 
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
 
Aircraft details
Aircraft manufacturer: S.A.A.B. Aircraft Co 
Aircraft model: 340 
Aircraft registration: VH-OLL 
Type of operation: Air Transport Low Capacity 
Damage to aircraft: Nil 
Departure point:Sydney, NSW
Departure time:1353 hours EST
Destination:Tamworth, NSW
 
 
 
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Last update 13 May 2014