Cessna Aircraft Company 310R, VH-COQ

Darwin air traffic control was using runway 29 as the primary
runway. Two BAe Hawk aircraft were approved to depart in the
opposite direction from runway 11. A Cessna 310 (C310) had departed
from runway 29 prior to the Hawks and was climbing through 3,500 ft
while tracking on the 107 radial of the Darwin VOR navigation
aid.

The planner controller had coordinated the clearance from runway
11 with the approach controller, who was performing both the
departure and approach control functions. However, the flight strip
indicated that the Hawks would depart from runway 29. As the
aircraft became airborne the error was detected, but the pair were
quickly closing on the C310. Traffic information was not passed to
any of the crews and the aircraft came within 1.5NM of each before
the Hawks had established themselves 1,000 ft above the altitude of
the C310. There was an infringement of separation standards, which
required a minimum of 3 NM horizontally or 1,000 ft vertically.

The investigation revealed that the planner controller had
carried out the correct coordination but had incorrectly written
runway 29 on the flight strip for the Hawks. When the aerodrome
controller coordinated the correct information to the approach
controller (using the phraseology "next runway one one"), the
approach controller was not alerted by the words "one one".
Consequently, the approach controller issued an instruction for the
Hawks to depart on runway heading still believing them to be using
runway 29.

When the pilots of the Hawks made radio contact with the
approach controller after departure, the controller chose to not
initiate evasive action as the rate of climb of the Hawks was far
greater than that of the C310, and they had already reached the
altitude of the C310. This decision was taken at a time when the
horizontal separation had reduced to less than the 3 NM standard.
The controller believed that the time taken to issue, and have the
pilots respond to, a turn instruction would take longer to attain a
horizontal standard than allowing the climb to continue until the
vertical standard was achieved.