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A research report released today by the ATSB reveals that the vast majority of loss of aircraft separation occurrences in Australia present little or no risk of collision, but more can be done to improve safety. (A loss of separation occurs when two aircraft under air traffic control come closer than a minimum separation distance.)

The report shows that Australia has one of the lowest loss-of-separation occurrence rates, attributable to civilian air traffic control, in the world. A loss of separation (LOS) between aircraft under air traffic control happens on average once every 3 days. In almost 90 per cent of LOS occurrences there was no or a low risk of aircraft colliding. Australia has about six LOS occurrences each year that represent an elevated safety risk. However, a LOS does not normally indicate that there was a near-collision between aircraft. There have been no midair collisions in Australia involving aircraft being provided with a separation service by air traffic control.

The report also reveals that half of all LOS occurrences are attributable to air traffic controller actions, while the other half result from pilot actions. The ATSB considers that more can be done to learn from LOS occurrences attributable to pilot actions in civil airspace.

The number of LOS occurrences under military control was found to be relatively high and most are the result of controller actions. The report finds that current regulatory arrangements do not enable the Civil Aviation Safety Authority (CASA) to give the same level of safety assurance for civilian aircraft under military control as it does for aircraft under civilian control. The ATSB has issued safety recommendations to the Department of Defence and CASA to address the safety issues identified in the report.

The release of this report coincides with the release of two other ATSB investigation reports into separate incidents (one near Ceduna, SA and the other about 900 km northwest of Karratha, WA) that involved losses of separation between passenger aircraft under air traffic control. As part of the Karratha investigation, the ATSB issued two safety recommendations to Airservices Australia. These recommendations were issued in response to the limited formal guidance available on the monitoring of newly endorsed controllers and the use of clearances that allow aircraft to operate anywhere between two flight levels, rather than at a single level.

All three reports are available on the ATSB website.

  • AR-2012-034   Breakdown of separation between aircraft in Australia: 2008 to 2011
  • AO-2011-144  Breakdown of separation - Boeing 737, VH-VXM and Boeing 737, VH-VUV, near Ceduna Airport, SA,  8 November 2011
  • AO-2012-012  Loss of separation between Airbus A320, 9V-TAZ and Airbus A340, A6-EHH near TANEM, 907 km NW of Karratha, WA, 18 January 2012

 


 

Fact Sheet

Loss of separation between aircraft in Australian airspace 2008 to 2012

How is aircraft separation maintained?

Air traffic controllers apply separation standards in controlled airspace to keep aircraft apart and to reduce the risk of collision. They do this by actively instructing pilots when, where and at what speed their aircraft can operate.

In high reliability systems such as Air Traffic Control (ATC), there are multiple risk controls in place that reduce the likelihood of human error occurring. However, on rare occasions an error will still occur. Additional risk controls or defences are in place to detect and recover from these errors, or mitigate the consequences. Those controls include route structures, monitoring by pilots and controllers, ATC system alerts (such as the short term conflict alert – STCA), aircraft traffic collision avoidance systems (TCAS) and visual see-and-avoid.

What is a loss of separation (LOS)?

A LOS occurs when the separation between two aircraft is less than the prescribed standard (vertically or laterally). This standard varies depending on the airspace classification. A LOS does not mean that the aircraft were at immediate risk of colliding or that the incident was a ‘near miss’. It means that the required separation standards were not maintained.

Do losses of separation represent a significant safety risk in Australia?

Data from international benchmarking shows that Australia’s civil Air Traffic Service-attributable loss of separation occurrence rates are among the lowest in the world. ATSB research reveals that a LOS between aircraft under air traffic control jurisdiction happens on average once every 3 days. In almost 90 per cent of LOS occurrences there was no or a low risk of aircraft colliding. Australia has about six LOS occurrences each year that represent an elevated safety risk. However, a LOS does not normally indicate that there was a near-collision between aircraft.

How does a LOS occur?

Both the air traffic controller and pilots of aircraft under the controller’s jurisdiction have responsibilities for establishing and maintaining separation. ATSB research shows that air traffic controller actions contribute to about half of all LOS occurrences while pilot actions contribute to the other half. Inevitably, human error will occur, but there are many levels of defence to safely manage the results of these errors. These defences ensure that even if a LOS does occur, the chance of aircraft colliding is very remote.

What can be done to improve the safety of aircraft separation in Australia?

While the vast majority of LOS occurrences present no or low risk, the ATSB has identified several safety issues that need to be addressed to further enhance safety. These include:

  1. More attention could be paid to learning from LOS occurrences attributable to pilot actions in civil airspace.
  2. While military only control a relatively small amount of airspace in Australia, the rate of LOS occurrences per aircraft movement is relatively high and most have contributing controller actions.
  3. Current regulatory arrangements do not enable the Civil Aviation Safety Authority (CASA) to give the same level of safety assurance for civilian aircraft under military control as it does for aircraft under civilian control.

The ATSB has issued safety recommendations to CASA and the Department of Defence to address these safety issues.

More information

The ATSB’s research report Loss of separation (LOS) between aircraft in Australian airspace – January 2008 to June 2012. This report provides a thorough analysis of loss of aircraft separation in Australia.

The ATSB’s website also contains investigation reports into LOS events.

Media contact: 1800 020 616
 
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Last update 18 October 2013