Cessna Aircraft Company 310 , VH-JOR

Coordination between the tower and terminal staff was unprofessional and led to confusion as to the status of visual approaches.
Various controllers had different interpretations of the meaning of "west" in relation to aircraft approaches.
A significant deterioration in the prevailing weather conditions coincided with the start of a busy arrival sequence.

As the flow controller was planning the arrival sequence, he needed to take account of the type of approach available to each aircraft. Even though visual approaches from the south-west had been in use during the morning, tower staff had advised the terminal area controllers that they were no longer available. However, the flow and approach controllers elected to continue with the plan that had the C310 as number one in the sequence and hoped that the pilot would be able to complete a visual approach. The conversations between tower and terminal area controllers in regard to the status of aircraft approaches took place between various control positions, each in partial isolation. Consequently, there was no coordinated response between tower and terminal area staff, and some confusion arose as to the status of such approaches.

As the C310 had been the first aircraft in a busy traffic sequence, the C310 needed to be repositioned when the pilot was unable to make a visual approach. When this re-sequencing occurred, pressure was on the system to try to make up some time to allow for the re-introduction of the C310. In order to minimise the delay, the approach controller had attempted to reduce the distance between the C310 and the AC50 by use of techniques that were not appropriate for the prevailing weather conditions.

The Cessna 310 (C310) was the first aircraft in a busy arrival
sequence and had been programmed by the flow controller for a
visual approach to right base for runway 15. The weather had been
fluctuating around marginal visual meteorological conditions for
some hours and although the cloud base was generally 2,500 ft, it
was lower in passing, heavier showers. The visibility was generally
8 km but reduced to 3,000 - 4,000 m in the showers.

When the pilot of the C310 reported that he was unable to
establish visual contact with the ground, the approach controller
had to change the arrival plan and vector the aircraft to the east
of the aerodrome to facilitate further descent. This amendment to
the traffic management plan was intended to assist the pilot to
become clear of cloud but it necessitated extra track miles for the
aircraft. Consequently, an adjustment to the arrival sequence was
required and the C310 became number three in the landing order.
This change also meant that the timing of sequential landings had
fallen behind that which the flow controller had planned and
following aircraft would need to be delayed.

The Aero Commander 500 S (AC50) was the fourth aircraft in the
sequence and had been held outside controlled airspace by the
approach controller until a separation standard could be guaranteed
with the other aircraft.

During the course of these events, several verbal exchanges took
place between various tower and terminal control area staff
regarding the availability of visual approaches in the
deteriorating weather conditions. It was agreed that all jet
aircraft, and other aircraft arriving from the north and west,
would be processed for instrument landing system (ILS) approaches.
While these conversations were taking place, the weather had
deteriorated such that the cloud base was 1,500 ft and the
visibility was generally 3,000 - 4,000 m.

The terminology of what was "north and west" was never
positively determined. The flow controller thought that the track
of the C310 (via Copperlode Dam - approximately 210 degrees from
Cairns) was south-west and not west. Other controllers considered
anything west of 180 degrees was "west" and would not have used
this track for a visual approach under the prevailing weather
conditions.

When the pilot of the C310 reported that he was "visual", the
approach controller authorised a visual approach and transferred
the pilot to the tower control frequency. Shortly after, he issued
a clearance for the AC50 to enter controlled airspace at 1,000 ft.
He judged that, as their observed ground speeds were similar, he
would be able to maintain the required radar standard of 3 NM while
keeping the aircraft comparatively close to each other in order to
minimise delays in the landing sequence.

As he was monitoring the progress of the aircraft, the approach
controller noticed that the groundspeed of the C310 had reduced on
final approach and that the 3 NM separation with the AC50 was
unlikely to be maintained. He asked the aerodrome controller if he
could use the "sight and follow" procedure, which would allow the
pilot of the AC50 to establish and maintain visual separation with
the C310 and, consequently, allow the distance between the aircraft
to reduce to below 3 NM. However, due to the deteriorating weather
and his resultant inability to sight the aircraft, the aerodrome
controller declined the request.

As the AC50 closed on the C310, the approach controller realised
that the 3 NM standard was not going to be maintained and asked the
aerodrome controller to visually separate the two aircraft, a
procedure that would again allow the aircraft to proceed with less
than the required radar standard. Once again, the aerodrome
controller declined the request as he could not see the aircraft in
the prevailing weather conditions.

The approach controller then decided to re-sequence the AC50 and
issued instructions for the pilot to turn away from the approach.
As the aircraft turned, the horizontal separation reduced to 2.8
NM. An infringement of separation standards had occurred.