Aviation safety investigations & reports

Loss of seperation assurance - Boeing 737, VH-VOB and Airbus A320, VH-VGZ, South 83 km Armidale NSW, 23 April 2011

Investigation number:
Status: Completed
Investigation completed


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On 23 April 2011, at 1644 Eastern Standard Time, a loss of separation assurance (LOSA) occurred between a Boeing B737-8BK (737), registered VH-VOB, and an Airbus Industrie A320-232 (A320), registered VH-VGZ, near Armidale Airport, New South Wales (NSW).

Both aircraft were conducting scheduled passenger services at flight level 320 on the same one way air route, H62, until position Mount Sandon, where the leading 737 aircraft would continue tracking south for Sydney, while the following A320 aircraft was flight planned to track left to Williamtown.

As the 737 was required to enter a holding pattern for sequencing into Sydney, the air traffic controller approved a speed reduction for the aircraft, but did not identify that the longitudinal separation between it and the following A320, was closing.

When the 737 flight crew provided the controller with their aircraft's speed information for the benefit of the following traffic, the controller identified the potential confliction and issued the A320 with a vectoring instruction to maintain separation. Although the separation between the two aircraft did not reduce below the required standard, a LOSA had occurred due to the closing longitudinal proximity between the two aircraft.

Airservices Australia (Airservices) advised that a review of LOSA and breakdown of separation occurrences would be undertaken to determine whether speed differential and aircraft performance were significant contributing factors and if additional refresher training was required for controllers.

This occurrence highlights the need for awareness of the effects of low workload on performance, identification of lowered vigilance and subsequent action or implementation of strategies to maintain safe operations. It also demonstrates how appropriate flight crew communication enhanced the situational awareness of the controller. In addition, the knowledge and application of effective compromised separation recovery techniques by the controller was integral in managing the situation.

Download Final Report - Bulletin
[Download  PDF: 5.43MB]
General details
Date: 23 April 2011   Investigation status: Completed  
Time: 16:45 EST   Investigation level: Short - click for an explanation of investigation levels  
Location   (show map): Armidale, south 83 km    
State: New South Wales   Occurrence type: Loss of separation assurance  
Release date: 12 December 2011   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft 1 details

Aircraft 1 details
Aircraft manufacturer The Boeing Company  
Aircraft model 737  
Aircraft registration VH-VOB  
Serial number 30622  
Operator Virgin Blue  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Brisbane, QLD  
Destination Sydney, NSW  

Aircraft 2 details

Aircraft 2 details
Aircraft manufacturer Airbus Industrie  
Aircraft model A320  
Aircraft registration VH-VGZ  
Serial number 3917  
Operator Jetstar  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Gold Coast, QLD  
Destination Williamtown, NSW  
Last update 14 November 2018