Aviation safety investigations & reports

Loss of separation assurance between an Airbus A320, VH-VNQ and a Boeing 737, VH-VZB, 50 km SSE of Hay Airport NSW, 30 August 2013

Investigation number:
Status: Completed
Investigation completed


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On 30 August 2013, a loss of separation assurance occurred between an Airbus A320, registered VH‑VNQ (VNQ), and a Boeing 737, registered VH‑VZB (VZB), 50 km SSE of Hay airport, NSW. VNQ was conducting a passenger flight from Melbourne, Victoria to Cairns, Queensland under the instrument flight rules (IFR). VZB was also conducting an IFR passenger flight in the opposite direction, from Cairns to Melbourne.

Both aircraft were operating in Class A airspace, under the control of an Airservices air traffic controller. The required separation standard in the portion of Class A airspace covered by radar surveillance was 5 NM laterally or 1,000 ft vertically. The majority of air routes in the airspace over which the controller had jurisdiction were one-way routes – aircraft could only operate in the direction marked on the aeronautical charts, but the Melbourne to Cairns route was a two-way route (T139). The airspace also contained a number of east/west routes that crossed T139.

Flight crews were required to plan flights in accordance with levels based on the magnetic heading of the planned track. Within controlled airspace, air traffic control (ATC) may assign and pilots may request a level that does not conform to this requirement. The crew of VNQ had planned to operate at FL360, and the crew of VZB had planned to operate at FL360 to a position inland and abeam Emerald, Queensland, and then at FL370 to Melbourne. However, the change of level planned by VZB had not been initiated, resulting in both aircraft converging at the same flight level.

The controller reported that their focus was on monitoring VNQ’s climb through the levels of a number of aircraft on crossing air routes and only became aware of the aircraft converging at the same level when the Short Term Conflict Alert (STCA) activated. The controller applied compromised separation techniques so that, while there was a loss of separation assurance, radar separation was not infringed.

As a result of this occurrence, Airservices will review the Melbourne to Cairns air route with regard to creating one-way routes, and more generally review similar routes nationally. In addition, Airservices has issued a directive reminding controllers of their responsibilities regarding the application of non-standard levels and subsequent return to standard levels.

In this incident, the timely activation of the STCA and the controller correctly utilising compromised separation techniques ensured that the separation standards were not infringed.


Aviation Short Investigation Bulletin - Issue 26

Download Final Report
[Download  PDF: 380KB]
General details
Date: 30 August 2013   Investigation status: Completed  
Time: 1624 EST   Investigation level: Short - click for an explanation of investigation levels  
Location   (show map): 50 km SSE of Hay Airport    
State: New South Wales   Occurrence type: Loss of separation assurance  
Release date: 25 February 2014   Occurrence category: Serious Incident  
Report status: Final   Highest injury level: None  

Aircraft 1 details

Aircraft 1 details
Aircraft manufacturer Airbus  
Aircraft model A320  
Aircraft registration VH-VNQ  
Serial number 5218  
Operator Tiger Airways Aust.  
Type of operation Air Transport High Capacity  
Sector Jet  
Damage to aircraft Nil  
Departure point Melbourne, Vic.  
Destination Cairns, Qld  

Aircraft 2 details

Aircraft 2 details
Aircraft manufacturer The Boeing Company  
Aircraft model 737  
Aircraft registration VH-VZB  
Serial number 34196  
Operator Qantas  
Type of operation Air Transport High Capacity  
Sector Jet  
Damage to aircraft Nil  
Departure point Cairns, Qld  
Destination Melbourne, Vic.  
Last update 14 November 2018