A Boeing 747-400 (B747-400) was en route from Singapore to Sydney at flight level (FL) 330 on air route A585, and a B747 was tracking in the opposite direction at FL350 from Melbourne to Jakarta on air route G222. The routes A585 and G222 converged at SAPDA, a position approximately 720 NM north-west of Broome on the boundary of the Australian and Indonesian flight information regions (FIRs). Route G222 was north-east of route A585 and the prescribed lateral separation point between the routes was 272 NM south-east of SAPDA. The aircraft were under the control of the Kimberley sector controller of the Brisbane centre.
The B747-400 was estimating SAPDA at 1811 Universal Coordinated Time and the controller approved that crew at 1747 to climb to FL350 at SAPDA. The Kimberley controller was advised at 1806 the B747 was at METUM, a position 252 NM south-east of SAPDA, at 1805 maintaining FL350 and estimating SAPDA at 1836. At 1812, the Kimberley controller received a SAPDA position report from the B747-400 crew and shortly after recognised there was no separation being applied between the aircraft. At 1813, the Kimberley controller instructed the B747-400 crew to descend to FL330, however there was an infringement of separation standards. The B747-400 crew subsequently reported maintaining FL330 at 1819.
The estimated time of passing of the aircraft was 1824. The Kimberley controller needed to establish the vertical separation standard of 2,000 ft between the aircraft before 1809 to ensure separation.
The Kimberley sector was a procedural sector operated by a single controller. Communication between controllers and flight crews could be by either:
- very high frequency (VHF) radio,
- controller pilot data link communication (CPDLC), or
- high frequency (HF) radio through a third-party radio operator.
The controller was communicating with the B747-400 crew using CPDLC and with the B747 crew by third-party HF radio. There was no VHF radio coverage in the portion of the sector in which the aircraft were operating.
The controller commenced the shift at 1300 (2300 Eastern Standard Time) and worked till about 1530 when he had a break. He returned to the position at 1610 and remained there until the occurrence. Normally during the period from 1400 to 1800, the number of aircraft in the sector gradually increased and after that time, traffic numbers decreased. The controller reported that there had been a busy period that had finished just before the occurrence. That was the controller's first shift following a 2-day break.
When the B747-400 crew requested approval to climb to FL350 via CPDLC, the controller checked for conflicting aircraft on the air situation display. At that stage, the B747 on G222 was over Western Australia and the controller reported that he might have perceived that aircraft as part of a group of aircraft on a more northerly route. Consequently, he coordinated a change of level with the adjacent Indonesian sector controller, and then instructed the B747-400 crew to climb at SAPDA.
The air traffic system had a flight plan conflict probe (FPCP) function to assist in the early identification of conflicts outside radar coverage. However, the FPCP had not been included in the commissioning of the new air traffic control system during 1998-99 and was not active.