A Tobago TB10 had departed Townsville on a night visual flight
rules flight which was on a track to the west of the airport. The
lowest safe altitude for the track was 5,200 ft and the pilot had
been approved by the approach controller to set course from
overhead the airport. Additionally, the approach controller had
required the pilot to remain east of the airport but over land, in
order to provide separation from other air traffic.
A BAe146 had taxied for a flight to Brisbane and the crew was
cleared for take-off on a runway 01 JEMMA 1 standard instrument
departure. That departure track involved a right turn after
take-off to a heading of 070 degrees with subsequent turns taking
the aircraft to the south-east of the airport.
The approach controller cancelled the requirement for the Tobago
to remain east of the airport as the conflicting traffic had passed
the conflict area. However, in cancelling the requirement, the
controller did not specifically instruct the Tobago pilot to track
on a westerly heading. The pilot remained over land, and east of
the airport, while continuing climb.
The BAe146 had departed and was in a right turn but the crew had
delayed transferring radio frequency to the approach controller in
order to report a bushfire that was burning north of the airport to
the aerodrome controller. During that time, the Tobago pilot had
commenced a right turn towards the north-east. Those actions
resulted in the aircraft being on conflicting headings without
instructions or amended clearances that would ensure the vertical
separation standard of 1,000 ft would be maintained.
The approach controller instructed the Tobago pilot to "take up
a westerly heading" but that instruction was not acknowledged. As
the BAe146 crew had not transferred to the departure radio
frequency, the controller instructed the Tobago pilot to turn to
the south in an attempt to maintain the 3 NM radar separation
standard as the there was less than 1,000 ft between the aircraft's
altitudes. The Tobago pilot acknowledged the instruction and, at
about the same time, the BAe146 crew transmitted on the departure
frequency. The approach controller then instructed the BAe146 crew
to turn left onto a heading of 090 degrees for avoiding action. At
that point, the Tobago was 3 NM away and on a closing heading.
Both crews carried out the instructions and radar analysis
indicated that the lateral and vertical distance between the
aircraft were 1.8 NM and 500 ft respectively. There had been an
infringement of separation standards that required 3 NM lateral or
1000 ft vertical separation.
Townsville Air Traffic Control was operated by the Royal
Australian Air Force. An investigation by the Directorate of Flying
Safety - Australian Defence Force revealed that the approach
controller had expected the Tobago pilot to take up a westerly
heading as soon as the requirement to remain east of the aerodrome
was cancelled. The approach controller also expected that the
tracks of the aircraft would remain more than 3 NM apart. The
unexpected actions of the Tobago pilot meant that the expectations
of the controller were not met and, when combined with the later
than normal radio transfer by the crew of the BAe146, left the
controller with few options to remedy the situation in a timely
manner.
The lack of the use of separation assurance techniques placed
the aircraft in a conflict situation.