The crew of a Boeing 747 (B747), maintaining flight level (FL) 390, en route from Cairns to Nagoya, was contacted by the crew of a Boeing 767 (B767), en route from Auckland to Osaka. The B767 crew reported that they had been approved by air traffic control to climb from FL370 to FL390, and that their position was 44 NM south-east of ASEDA, which is located within the Tokyo oceanic control area. The B747 crew reported that they were 54 NM south-east of ASEDA at FL390. Subsequently, the B767 crew advised that they would limit their climb to FL385. Shortly after that exchange the sector controller instructed the crew of the B767 to descend to FL370 due to traffic.
An investigation found that the sector controller was managing five aircraft tracking north on air route A597, together with an aircraft crossing A597. The controller was concerned that the longitudinal separation between the B767 and another following aircraft at FL370 would reduce to less than the required standard, which was either 2,000 ft vertically or 15 minutes longitudinally. Consequently, the controller instructed the B767 crew to climb, but failed to appreciate that the B767 would conflict with the B747 at FL390. However, the controller subsequently recognised that an error had been made and issued alternative instructions.
