A Boeing 767 aircraft, VH-RME, departed Hamilton Island for Sydney at 1348 EST and was assigned an initial flight level (FL) 270 due to crossing traffic over Hamilton Island, which was climbing through FL280. Further along the aircraft's intended route there was another possible confliction with another Boeing 767, VH-OGM, tracking from Cairns to Brisbane at FL370. The tracks of the two aircraft crossed at a point approximately 95 NM south of Mackay.
As RME approached Mackay from the north, the Sector 7S controller asked the pilot at what distance south of Mackay the aircraft would be on reaching FL390. The pilot advised that he would reach FL390 by 40 NM south of Mackay.
The two aircraft would not be in conflict until approximately 80 NM south of Mackay, and the controller therefore issued a clearance to the pilot of RME to climb to the planned level of FL 410, with a requirement to reach FL390 by 70 NM south of MacKay. The pilot read back the clearance correctly. The controller subsequently noticed the aircraft at approximately 67 NM south of Mackay, climbing through FL350.
The controller asked the pilot to confirm that the requirement would be met. The pilot replied in the affirmative, but shortly after advised that he could not meet the requirement. The controller instructed the pilot to turn left 30 degrees for separation, and issued traffic information on OGM. The aircraft came to within 10 NM on parallel tracks. When RME had left FL 390, the pilot was cleared to resume tracking via the flight planned route.