Loss of separation involving a The Boeing Company 737-376, VH-TAJ and British Aerospace PLC BAe 146-100A, VH-NJC, 185km E Alice Springs, Aerodrome, NT on 14 September 1993

VH-NJC, was en route from Cairns to Ayers Rock cruising at flight level (FL)280. VH-TAJ, was en route Darwin to Adelaide, cruising at FL330. The crossing point of the two tracks was approximately 100 nautical miles east of Alice Springs. Near the intersection of the two tracks, the pilot of VH-TAJ requested a clearance from air traffic control to desend to FL270. This was approved. Subsequently the air traffic controller realised VH-TAJ did not have the required lateral separation from VH-NJC. He checked the level of VH-TAJ but the aircraft had left FL285 on descent. The aircraft was allowed to continue the descent as both aircraft were well clear of each other, but within the area of lateral confliction.