Loss of separation involving a Boeing 767-277, VH-RME and Boeing 747-438, VH-OJA, Cullerin, New South Wales, on 10 December 1997

A domestic Boeing 767 was inbound to the holding pattern at Cullerin and the crew had been issued a requirement to reach their assigned level of FL 290 before entering the pattern. The crew of a Boeing 747 already established in the Cullerin pattern observed the inbound aircraft descending through its assigned level and alerted ATC. The descending aircraft was visually sighted and was displayed as traffic on the TCAS.

The pilot of the descending B 767 indicated that the autopilot had not captured the assigned level as programmed. The pilot indicated that this was possibly complicated by late amendments to the holding instruction. The crew intervened when it became apparent that the autopilot had not captured the assigned level, but not before the aircraft had descended approximately 400 ft through the assigned level.

The controller indicated that 1,000 ft vertical separation between the two aircraft was quickly re-established, and the aircraft were horizontally separated by 3 - 4 NM.