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A Cessna 340 (C340) departed Sydney at 1036, on climb to flight level (FL) 120, tracking via Shellys and Yass to Deniliquin. At 1047 a Saab 340B (Saab) departed Sydney for Canberra on climb to FL120, also tracking via Shellys. Once both aircraft were established in cruise there was a rate of closure of about 100 kt between them. As the Saab passed over Shellys, the Melbourne Sector 12 controller observed on radar that the lateral separation between the two aircraft was reducing to less than the required standard of 5 NM. The controller instructed the Saab to turn left though 90 degrees and advised the crew that there was traffic in their 2-o'clock position at 2 NM. The crew reported sighting the C340. Subsequent radar analysis established that the lateral distance between the aircraft had reduced to 2 NM.

The traffic level in the sector was low, with six aircraft on frequency. The controller had been operating the radar display on the 100 NM scale to enable him to readily observe boundary traffic or approaching flights. The display was centred on Shellys at the time of the occurrence. The controller was closely monitoring the progress of three aircraft that were tracking between Wollongong and Canberra. Two aircraft were in a step climb, while the third was overtaking and outclimbing the first two. The controller believed that he was maintaining an adequate scan of the radar display and was unable to provide a reason for not appreciating the effect of the high rate of closure between the two occurrence aircraft.

The morning shift of the adjacent sector to the west of Sector 12 had transitioned to The Advanced Australian Air Traffic System (TAAATS) approximately two and one-half weeks prior to the occurrence. This had resulted in the implementation of a number of changes to Sector 12 coordination procedures. Those changes were only required during the morning shift. During the afternoon the adjacent sector reverted to the same air traffic control system as that being used by Sector 12. The controller subsequently reported that while the amended coordination procedures were understood, they required conscious thought to action them.

During the morning, and at the time of the occurrence, coordination between the sector and Nowra Air Traffic Control had been restricted by communications problems and the controller was using a "hotline" and a telephone for coordination. There was no telephone available on the Sector 12 console so the controller was required to reach across to use one from an adjacent console.

The investigation did not establish the reason why the controller was unaware of the impending conflict until there was insufficient time to resolve the situation. It is probable that a combination of low traffic levels, possible fixation on the Wollongong - Canberra traffic situation, and some distraction due to amended coordination requirements, was sufficient to reduce the controller's normal level of vigilance.

General details
Date: 10 May 1999 Investigation status: Completed 
Time: 1108 hours EST  
Location   (show map):Shelleys, (NDB) Investigation type: Occurrence Investigation 
State: New South Wales Occurrence type: Loss of separation 
Release date: 29 July 1999 Occurrence class: Airspace 
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
Aircraft 1 details
Aircraft manufacturer: S.A.A.B. Aircraft Co 
Aircraft model: 340 
Aircraft registration: VH-EKN 
Serial number: 372 
Type of operation: Air Transport Low Capacity 
Damage to aircraft: Nil 
Departure point:Sydney, NSW
Departure time:1047 hours EST
Destination:Canberra, ACT
Aircraft 2 details
Aircraft manufacturer: Cessna Aircraft Company 
Aircraft model: 340 
Aircraft registration: VH-MAG 
Serial number: 3400166 
Type of operation: Unknown 
Damage to aircraft: Nil 
Departure point:Sydney, NSW
Departure time:1036 hours EST
Destination:Deniliquin, NSW
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Last update 13 May 2014