Breakdown of co-ordination involving a Boeing 727-277, VH-ANA, 270 km north of Sydney, New South Wales, on 6 April 1993

VH-ANA [B727] was enroute from Brisbane to Sydney at Flight Level [FL] 330. At 0949 hours EST the crew were authorised by Sydney air traffic control [ATC] to descend, when ready, to FL 280. One minute later this clearance was cancelled by ATC and VH-ANA was required to maintain FL 330. The aircraft had not commenced descent.

All Nippon Airways 914 [B747] had departed Sydney for Narita [Japan] and was climbing to an initial altitude of FL 280. The track of this aircraft would cross that of VH-ANA approximately 120 NM north of Sydney.

All Nippon Airways 914 was given climb to FL 310 at 0946 hours and, due to a busy period of air traffic, this change of level was not co-ordinated until 0949 hours. On receiving the notification of the level change, the controller responsible for VH-ANA took immediate action to reintroduce procedural separation before radar separation was lost.

The aircraft passed at 0951 hours with 2,000ft vertical difference. There was no breakdown in separation standards.