de Havilland Canada DHC-7-102, VH-UUM, 13 km WSW Cairns, Aero. QLD, 17 November 1999

The crew of the Dash 7, registered VH-UUM, were cleared to track
visually via Kuranda. The crew of the Cessna 310, registered
VH-XXT, were cleared to track visually via Stoney Creek. Both
aircraft had flight planned IFR and were entitled to positive air
traffic control separation. Such separation was not provided and
the required radar separation standard of 3 NM between the two
aircraft was infringed. The investigation revealed that the
strategy for separation employed by the approach controller did not
provide a separation standard. Radar separation was an option, in
accordance with the Manual of Air Traffic Services (MATS), 9-2-1,
paragraph 19, if the departing aircraft had been issued a standard
radar departure. Such a departure was not provided. Moreover,
because vertical separation had not been employed, the controller
had to rely on lateral separation to ensure the aircraft did not
conflict. However, lateral separation would not exist if both
aircraft were simultaneously east of a line Stoney Creek-Kuranda.
There was no separation assurance. MATS 4-1-1, paragraphs 4-6 place
significant emphasis on the need for controllers to apply
separation assurance techniques. Realising the potential
confliction after take-off, the controller attempted to establish a
visual sighting of the departing aircraft by the crew of the
arriving aircraft. The visibility was reduced due to smoke haze,
making a sighting unlikely. If a sighting had been achieved, it
would have allowed the transfer of separation responsibility from
the controller to the pilot. The crew of the arriving aircraft were
unable to sight the departing aircraft. The controller then
requested the crew of the arriving aircraft to make a right orbit
but the crew were unable to comply due to high terrain. The crew
suggested a left orbit, which was agreed to by the approach
controller. The left orbit however, further reduced the distance
between the two aircraft. The crew of the departing aircraft then
sighted the arriving aircraft, with the assistance of the
aircraft's TCAS, and were able to visually maintain separation.
Vertical separation was reduced to 100 ft when the aircraft were
1.5 NM apart. The required radar separation was 3 NM or 1,000 ft
vertically.