At the time of the incident, Brisbane ATC Sector 11K Radar and Sector 11 Procedural were being operated as a combined control position. Tindal radar was out of service. A Sector 11K Radar trainee, who was already rated on Sector 11 Procedural, was operating the combined position under the supervision of a training officer.
A Westwind aircraft was tracking Darwin - Tindal - Alice Springs and climbing to Flight Level 330 (FL330), with an estimate for overhead Tindal of 1911 CST. A Boeing 747 (B747) was tracking in the opposite direction to the Westwind and estimating overhead Tindal at 1912. The Westwind was still displayed on radar, but the B747 was outside radar coverage.
Two other aircraft were also under the control of the trainee. The trainee initiated co-ordination with Melbourne ATC to amend the clearance for one of these aircraft. Before Melbourne ATC answered, the pilot of the Westwind requested an amended level of FL370. The trainee immediately cleared the Westwind to this level. Shortly afterwards, the crew of the B747 reported that there was traffic 1,000 feet below their aircraft. (The crew later advised that they had received a Traffic alerting and Collision Avoidance System (TCAS) traffic alert on the other aircraft.) The Westwind was observed on radar to be climbing and approaching FL340. The controller instructed the Westwind pilot to maintain FL340 and, immediately afterwards, to descend to FL330. He informed the Westwind pilot of the relative position of the B747.
The investigation determined that the two aircraft had passed with approximately 1.5 NM lateral separation, as the Westwind descended through FL335 and the B747 maintained FL350. In the procedural control environment existing at the time, the required vertical separation standard was 2,000 ft. The required lateral separation standard was 10 minutes combined flight time.
Neither the trainee controller, nor the training officer, checked the flight progress strips for the two aircraft prior to the Westwind being cleared to climb to FL370. The training officer was checking lateral separation calculations for other traffic on a map at the time and was not closely monitoring the trainee.