air safety

Feb 27, 2013

Darwin inquiry into near miss by two jet airliners updated

Last October a Qantaslink 717 approaching Darwin Airport from Alice Springs, and a Qantas 737-800 that was climbing away on a flight to Melbourne were misdirected by military air traffi

Ben Sandilands — Editor of Plane Talking

Ben Sandilands

Editor of Plane Talking

Last October a Qantaslink 717 approaching Darwin Airport from Alice Springs, and a Qantas 737-800 that was climbing away on a flight to Melbourne were misdirected by military air traffic control to a situation in which the outbound jet passed under the inbound jet with only 900 feet to spare.

This is but one of a number of disturbing air traffic control standards breakdowns that have recently occurred to scheduled passenger flights that come under military ATC control at Darwin and at Williamtown which is also used as Newcastle’s airport.

The ATSB has updated its investigation into that incident as follows:

On 2 October 2012, a loss of separation occurred between a Boeing 717 (717) aircraft, registered VH-NXQ and operating a scheduled passenger service from Alice Springs to Darwin, Northern Territory, and a Boeing 737 (737), registered VH-VXM, operating a scheduled passenger service from Darwin to Melbourne, Victoria. The aircraft were under the jurisdiction of military air traffic control (ATC) at the time of the occurrence.

At 1338 Central Standard Time, Brisbane Centre handed over control of the 717 to Darwin ATC. The crew had been cleared to descend from flight level (FL) 320 to 10,000 ft and track direct to Darwin for runway 29.

At about this time, the call sign label for the 717 was assigned to another aircraft in the Australian Defence Air Traffic System (ADATS) and displayed on the Approach controller’s radar display (as ‘NXQ’). The other aircraft was overflying the airspace at FL 260 and not on the Approach controller’s frequency, or under approach control at the time. The actual radar return for the 717 was displayed on the controller’s display as an unlabelled track.

At 1341, the 737 departed runway 11 on climb to FL 130 on a heading of 170 degrees to separate it from another aircraft. The departure was the last movement on runway 11 before a switch to runway 29.

At 1342, the 717 was passing FL 112 and the crew requested further descent. The Approach controller queried the aircraft’s flight level and the crew advised they were at 10,500 ft. The controller responded that their displayed altitude was FL 260. At that stage, the controller thought that the 717 was the aircraft incorrectly displayed as NXQ and located to the south-west of Darwin at FL 260. The flight crew were requested to maintain 10,000 ft and to recycle their transponder. After further communications, the controller cleared the crew to descend to 7,000 ft. At 1344:01 the crew advised that that they were 18 NM (33 km) from Darwin and leaving 10,000 ft.

The traffic confliction was detected by the 717’s flight crew and they did not initiate their descent from 10,000 ft. Concurrently with the activation of ADATS’ predictive conflict alerts, the Approach Supervisor identified the conflict and directed the Approach controller to commence separation recovery procedures. At 1344:20, the Approach controller instructed the 737 crew to stop their climb at 9,000 ft. At that stage the aircraft was displaying 8,400 ft and climbing. At 1444:32 the crew of the 717 advised the controller of conflicting traffic below them and the controller instructed them to stop descent.

Radar data indicated that the 737 climbed to 9,100 ft before descending back to 9,000 ft and the 717 remained at 10,000 ft. The separation reduced to about 900 ft vertically as the 717 passed directly overhead the 737 on a reciprocal track. The required separation standards were either 1,000 ft vertical separation or 3 NM (5.56 km) radar separation.

ATSB investigators have interviewed Darwin air traffic controllers and conducted a site visit to Darwin air traffic control. The investigation is continuing and will include:

  • further analysis of the radar and audio data
  • review of the functionality of ADATS and related systems, including the messaging interface with the civilian air traffic computer system
  • review of the workspace equipment layout for control positions in Darwin
  • review of air traffic control procedures, documentation and training.

The ATSB aims to finalise this investigation in October 2013.

There are several questions that arise from the sections of the update that have been emphasised above in bold type.

Why would a civil airliner tag be assigned to a military flight?

Why would the track of the approaching 717 be left unlabelled on the ATC console screen?

These are important questions and October this year is a long time to wait for answers.

Despite its post Pel-Air aversion to making safety findings and recommendations, it is hoped that the ATSB gets over that disgraceful abrogation of its obligations and gets on with its real job, which is not protecting CASA from embarrassing diclosures.

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3 thoughts on “Darwin inquiry into near miss by two jet airliners updated

  1. Wild Bill

    Ben, to answer your questions:
    The system used by military ATC (ADATS as its locally known) is outdated and half the functionality does not work. This is a separate discussion however!
    Labels on the Radar screen frequently switch when you have two paints that come in from opposite sides of the Radar at similar position. It’s called a label swap by Mil ATC. There is also an issue with ‘Ghosting’, where a fictitious paint is displayed on the opposite side of the screen to an inbound aircraft, however it’s normally a primary paint only. The label should automatically be assigned to an aircraft that is inbound and squaking a discreet code, which would have been the case of the 717. That said, the label swap should have been detected by the APR controller given that the MIL ACFT and the 717 were inbound on very different tracks.

    My question is why if the 737 was instructed at 8,400ft to stop climb at 9,000ft did they bust the level by 100ft? Surely they would not have been at such a rate of climb that arresting it in 600ft was not possible? If they had stopped at 9,000ft as assigned, then this issue would not have been attracting any attention.

    That said, it is evident that there are fundamental issues being experienced by MIL ATC, predominately due to a lack of experience, and retention issues with senior controllers. This is the real issue that should be discussed.

  2. Nasty Go Round

    That sounds like a shambles.

  3. ghostwhowalksnz

    With the military use of the airport only a fraction of the the general and commercial use , why are military ATC and systems even being used

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