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Summary

Summary

The aircraft departed two minutes apart from Kalgoorlie enroute to Perth. The first aircraft, BAe 146 VH-NJZ, was cleared by the sector air traffic controller to track via Southern Cross on planned route climbing to FL240. The route followed the 255 degree radial from the Kalgoorlie VOR. When the pilot of the second aircraft, Boeing 737 VH-CZP, contacted the sector controller for a clearance, he advised that the aircraft was avoiding weather and tracking the 240 degree radial from Kalgoorlie VOR. The sector controller subsequently cleared CZP to track via the Nalar Dulya route on climb to FL350. The pilot of CZP was communicating with the pilot of NJZ on the flight service frequency to ensure separation was maintained between the aircraft during the weather avoidance. The FSO reported to the sector controller that the pilot of CZP advised that he was initially tracking outbound on the 257 degree radial from the Kalgoorlie VOR and was now paralleling track. When queried by the sector controller, the pilot of CZP advised that the aircraft was on approximately the 246 degree radial from the Kalgoorlie VOR and was leaving FL210 on climb. The controller instructed the pilot of CZP to maintain FL210, to which the pilot replied that the aircraft was leaving FL220 on descent to FL210. The pilot of NJZ was immediately queried by the sector controller about his altitude and he reported that his aircraft was leaving FL225 on climb. The investigation revealed that it was unlikely that a breakdown in separation occurred because the pilots appeared aware of their relative positions and maintained separation. However, the sector controller took action to ensure procedural separation was maintained based upon the information available to him.
 
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