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A Metroliner had departed Darwin on a flight to Dili, East Timor. The crew had climbed to flight level (FL) 180 and were maintaining that altitude. They had been under the control of Darwin Air Traffic Control for the first 60 NM and had transferred to Brisbane Control in accordance with normal procedures. They had established two-way radio communication with Brisbane sector control.

 

History of the flights

A Metroliner had departed Darwin on a flight to Dili, East Timor. The crew had climbed to flight level (FL) 180 and were maintaining that altitude. They had been under the control of Darwin Air Traffic Control for the first 60 NM and had transferred to Brisbane Control in accordance with normal procedures. They had established two-way radio communication with Brisbane sector control.

The Airbus A330 (A330) was on a flight from Kuala Lumpur, Malaysia to Darwin and the crew had commenced descent to FL210 in accordance with instructions from Brisbane Control.

When the A330 was approximately 97 NM from Darwin, the crew requested further descent. The Brisbane controller immediately activated the intercom line to Darwin Approach and informed the Darwin controller of the position of the A330. The Metroliner was 81 NM from Darwin at that time.

The Darwin controller, who was under training, only had access to a 60 NM radius display screen. He had already handed off the outbound Metroliner to the Brisbane controller and authorised descent to FL 120 for the A330 in the belief that the Brisbane controller would separate the two aircraft. The trainee was not immediately aware of the relative positions of the aircraft as the conflict was not shown on his display.

The training officer immediately realised that separation had not been assured by the coordination interaction and looked to one side where he had set up a second screen display on an adjacent console. He had selected a greater range scale on the console, that showed the position of the two aircraft. As he was briefing the trainee on urgent action to remedy the situation, the crew of the A330 reported on the Darwin Approach radio frequency that they were on descent to FL120. While that radio exchange was occurring, the trainee had selected the longer range scale on his console and the display had now appeared on his screen. It showed that the aircraft were approximately 9 NM apart in a nose-to-nose conflict. He immediately issued an amended instruction to the crew of the A330 to maintain FL190. The crew was able to carry out that instruction before the vertical separation standard of 1,000 ft was infringed.

A few moments later the captain of the Metroliner saw the A330 pass immediately overhead. He reported that there was insufficient time to draw the co-pilots attention to the aircraft before it passed. He was of the opinion that there would have been insufficient time to initiate an evasive manoeuvre if it had been required.

The A330 crew saw the Metroliner but took no action as the aircraft were obviously going to miss. The traffic alert and collision-avoidance system was serviceable but did not activate.

Radar analysis indicated that the aircraft passed with approximately 1,300 ft vertical separation but with no horizontal difference.

At the Brisbane sector console, the short term conflict alert activated approximately 20 seconds prior to the time of passing. The controller immediately checked the radar display and found that a separation standard was being applied by Darwin approach control and took no further action.

Darwin approach control

The Darwin approach unit controlled airspace to 60 NM, in the north west quadrant, up to and including FL200. At the time of the coordination from Brisbane sector, both aircraft were outside those parameters and, therefore, not subject to direct control by Darwin.

Local procedures required that arriving aircraft be assigned no lower than FL210 by Brisbane Control. Therefore Darwin Control was required to approve any further descent despite the aircraft being in Brisbane's airspace. When the Brisbane controller coordinated the position of the A330, the trainee read into the tone of the voice that a request was being made for further descent even though the actual words used did not state that intent. The trainee was not immediately aware of the confliction because it was outside his area of jurisdiction and not within the range of his selected display. The trainee also had the impression that, as the aircraft were in Brisbane's airspace, he was only approving descent in Darwin's airspace and that the Brisbane controller was still responsible for the separation of the aircraft.

Radar hand-off was the subject of a specific instruction in the Manual of Air Traffic Services Supplement (MATS Supp) which stated: "Aircraft handed off by radar between Darwin ATC and Brisbane/Tindall Sectors shall be subject to `no restrictions' unless otherwise advised."

The adjacent console was not in use and had been positioned so that the controllers could view the display screen, albeit at a distance of 2 - 3 m. The range was selected at a longer distance than the 60 NM in use at their primary screen. That selection meant that the position of the aircraft could be seen but the details in the information blocks could not be read. A software change was scheduled for introduction the next day that would have allowed the trainee to view the longer range (second look) on his own console rather than having to look across to the second screen.

When the trainee had approved descent for the A330, the Brisbane controller de-selected the intercom line before the training officer could intervene to cancel the approval. The training officer immediately briefed the trainee to maintain the A330 at FL190 because he expected the crew to change frequency quickly as, in his experience, they normally did. The training officer was prepared to go back to Brisbane via the intercom line, but the broadcast by the crew of the A330 made that option redundant.

Brisbane sector control

The controller coordinated the position of the A330 with Darwin Control and expected an instruction from Darwin regarding descent. When they issued approval for FL120 he assumed that they were separating the aircraft, even though he thought that he may not have looked at his display at the time of carrying out the coordination and may have, momentarily, overlooked the actual position of the Metroliner. He then issued the descent instruction and told the crew to change radio frequency to Darwin Approach.

Shortly after, the short term conflict alert activated and the controller immediately checked the display. He saw that there was no infringement of separation standards and took no further action.

The controller had been rated on The Australian Advanced Air Traffic System (TAAATS) for 4 months but had just returned from a month's leave. He received 2 days familiarisation and had performed 4 active shifts prior to the occurrence. He stated that he was well rested and that the workload was moderate. However, he said that he was a bit `rusty' and that the 2 days familiarisation was a bare minimum for adequacy.

Short term conflict alert

The activation of the alert was to warn the controller that the aircraft were predicted to pass within 600 ft and 4.1 NM. Analysis of the performance of the alert indicates that it operated in accordance with the parameters and provided approximately 20 seconds warning of the conflict.

 

Airspace management

The general control technique to ensure separation on this route was for Darwin to assign FL200 (or below) for departures and for Brisbane to only assign FL210 for descent; therefore ensuring the 1,000ft separation standard.

In accordance with MATS Supp, when an aircraft was handed off from one controller to the other, that aircraft shall be subject to "no restrictions" unless otherwise stated. In the case of the A330, the Brisbane controller had not mentioned any restrictions for its descent and had, therefore, incorrectly coordinated the aircraft with Darwin. Darwin Control had correctly coordinated the Metroliner with Brisbane Control and had transferred the crew to the Brisbane controller's radio frequency before that aircraft had left their area of responsibility. As the Metroliner had passed outside 60 NM from Darwin, it was under the control of the Brisbane controller. Had the crew of the A330 been slow with their radio frequency transfer, neither controller would have been able to prevent the A330 descending through the level of the Metroliner.

Darwin approach control

The trainee controller made a decision to allow the A330 further descent based on a belief that the Brisbane controller would separate the aircraft that were in that controller's airspace. However reasonable that belief may have been, the approval left open a possibility for an infringement in separation standards. Phraseologies to ensure separation were available and would have clarified that the descent was subject to the Brisbane controller's separation of the aircraft.

The intended action of the training officer was appropriate and timely, but the broadcast from the crew of the A330 made his plans redundant.

Had the software change that was to be implemented the next day been available at the time, the trainee would have had a better opportunity to see the relative positions of the aircraft and, therefore, observe the developing air traffic situation and take more appropriate action.

Brisbane sector control

When the response from Darwin Control was for descent to FL120, the controller accepted the level and issued descent to that level to the crew of the A330 when the aircraft were approximately 16 NM apart and with a closing speed of approximately 12 NM per minute. Irrespective of the response from Darwin, the Brisbane controller still had responsibility for separation of the aircraft outside the 60 NM arc and the aircraft were obviously going to pass in that controller's airspace. The controller also had both aircraft on his radio frequency and the instruction to the crew of the A330 gave away both separation and radio contact. However, the crew of the A330 made a timely and successful change of frequency to the Darwin controller. Had this transfer taken longer to take place, the only solution would have been for the Brisbane controller to issue emergency instructions to the crew of the Metroliner. As the controller had considered that Darwin were separating the aircraft at the time of issuing the A330 descent, it is unlikely that such action would have been taken in time.

 
  1. The Brisbane sector controller did not ensure separation between two aircraft that were on his radio frequency and in airspace that was under his jurisdiction.
  2. The Brisbane sector controller did not provide a "no restrictions" hand-off to the Darwin controller.
  3. The Darwin approach trainee authorised a level change without ensuring separation.
  4. The introduction of a software change that would have enabled the Darwin trainee to view the relative positions of the aircraft, was scheduled for implementation the day after the occurrence.
 

Local safety action

The Darwin Australian Defence Air Traffic System software was upgraded on 14 June 2000 to allow a "second look" access to controllers at each console.

 
General details
Date: 13 June 2000 Investigation status: Completed 
Time: 0730 hours CST  
Location   (show map):167 km NW Darwin, Aero. Investigation type: Occurrence Investigation 
State: Northern Territory  
Release date: 02 November 2001 Occurrence class: Airspace 
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
 
Aircraft 1 details
Aircraft manufacturer: Fairchild Industries Inc 
Aircraft model: SA227 
Aircraft registration: VH-ANY 
Serial number: DC-840B 
Type of operation: Air Transport Low Capacity 
Damage to aircraft: Nil 
Departure point:Darwin, NT
Destination:Dili, East Timor
Aircraft 2 details
Aircraft manufacturer: Airbus Industrie 
Aircraft model: A330 
Aircraft registration: 9M-MKC 
Type of operation: Air Transport High Capacity 
Damage to aircraft: Nil 
Departure point:Kuala Lumpur, Malaysia
Destination:Darwin, NT
 
 
 
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Last update 13 May 2014