The Brisbane terminal area was busy, and both aircraft were required to enter a holding pattern at Maroochydore. VH-EWG was to be the first of the two aircraft to land at Brisbane, but because the pilot had slowed the aircraft enroute, VH-TAY had already entered the holding pattern at a lower level than VH-EWG.
When a preceding aircraft left the holding pattern on descent for landing at Brisbane, the air traffic controller responsible for the holding aircraft descended VH-EWG through the level of VH-TAY without the required lateral separation. At the time both aircraft were heading in the same direction with VH-TAY travelling at a faster speed. The controller realised his mistake and instructed VH-EWG to climb. Separation was reduced to 2.5NM instead of the required 5NM. The controller was relatively inexperienced at the control position he was working and the workload at the time was high.
