A Brasilia VH-XFZ was on a visual approach to Cairns from the south-east and was tracking to left base runway 15. A Citation VH-PSU departed from runway 15 without a separation standard being applied by the approach controller between the two aircraft. The aircraft passed with approximately 500 ft difference in their altitudes when there was less than 3 NM laterally between them.
The controller could have either coordinated the use of a visual separation procedure with the aerodrome controller or the crew of either aircraft, or employed a 1,000 ft vertical separation standard or a 3 NM radar standard to ensure that the aircraft were separated.
The investigation revealed that the controller was aware that a separation standard was required. This was confirmed by the controller's request to the pilot of XFZ to report seeing PSU that was shortly to depart. However, subsequent actions limited the ability of the pilot of XFZ to comply with the request. If this sighting had been achieved, it would have allowed the transfer of separation responsibility from the controller to the pilot. This procedure did not provide separation assurance and was a "fail-unsafe" procedure as it relied solely on the pilot's ability to see the other aircraft and limited the controllers' options should the pilot be unable to comply.
When the crew of XFZ were unable to sight PSU the controller then monitored PSU's climb performance and assessed that the aircraft would not collide. However, vertical separation reduced to less than the standard when there was no radar standard being applied.
The use of a radar standard was constrained by the disposition and intended tracks of the aircraft. In this situation, the Manual of Air Traffic Services (MATS), 9-2-1, paragraph 19 states that a procedural separation standard shall be applied. Also, the controllers actions did not comply with MATS 4-1-1, paragraphs 4-6 which places greater emphasis on traffic planning and conflict avoidance by controllers instead of conflict resolution. The use of separation assurance techniques by the controller would have ensured the separation of the aircraft.