The Cessna Aircraft Company 402C (Cessna) was established on
final for a straight-in approach to runway 15 at Cairns. The pilot
had been assigned a descent to 3,000 ft, due to a de Havilland
Canada Dash 8 (Dash 8) that was on final approach ahead of the
Cessna and was at or below 2,000 ft. The assigned altitude ensured
that the 1,000 ft vertical separation standard was maintained. The
Approach One controller did not notice the Cessna descend through
3,000 ft or that the ground speed of the Dash 8 had reduced such
that the spacing between the aircraft was less than the required 3
NM radar separation standard. There was an infringement of
separation standards. The weather was reported to be fine with a
clear sky.
Cairns approach control was managed by two control positions;
Approach One and Approach Two. The Approach One area of
responsibility was over the sea and included the final approach for
runway 15 and all departures. Approach Two was responsible for the
area over land.
The Approach One controller had accepted responsibility for the
position about 10 minutes before the occurrence. The controller had
been the Flow controller for the afternoon and was due to finish
his shift at 1830 Eastern Standard Time. Prior to leaving, he
offered to take over Approach One to enable another controller to
take a short break. A handover/takeover was conducted at the
Approach One position and he was aware of the six aircraft in the
arrival sequence; having established the sequence himself while in
the Flow position. He was also aware of another four aircraft
taxiing for departure.
The initial aircraft in the arrival sequence were a Twin Otter
from Mackay, the Dash 8, the Cessna and then an Embraer Bandeirante
from the west. The Approach One controller was responsible for the
Twin Otter, Dash 8 and the Cessna, while the Bandeirante was under
the control of the Approach Two controller.
The Twin Otter crew had been assigned a visual approach for left
base to runway 15 but subsequently requested an instrument landing
system (ILS) approach. Approval of the ILS would entail additional
track miles and reduce the spacing between the Twin Otter and the
Dash 8. The controller believed sufficient spacing for separation
and sequencing would be maintained with some minor track
adjustments. He instructed the Dash 8 crew to turn left heading 330
degrees and to descend to 3,000 ft to position the aircraft east of
the coast and 6 miles behind the Twin Otter. About two minutes
later the controller instructed the Dash 8 crew to descend to 2,000
ft and the pilot of the Cessna to descend to "3000 (ft) visual".
Those instructions were appropriately acknowledged by the crews. As
the Cessna was from the north, and effectively on a long final, the
controller issued the instructions to establish the vertical
separation standard between the aircraft.
The Approach One controller instructed the Dash 8 crew to turn
left heading 250 degrees and to descend to 1,500 ft. The crew was
aware of aircraft arriving from the north. As the Dash 8 approached
the runway 15 extended centreline, the crew thought the approach
controller may have forgotten them and they discussed whether or
not to contact the aerodrome controller direct. The crew could see
the terrain to the west and reduced the aircraft's speed to reduce
the rate of closure with the terrain. Shortly after, the Approach
One controller instructed them to make a visual approach. That
required them to turn the Dash 8 approximately 140 degrees to the
left and then turn back to the right to establish the aircraft on
final for runway 15. The crew did not report, nor were they
required to report, their reduced speed. The controller could
monitor aircraft ground speeds via the air situation display radar
track labels.
The pilot of the Cessna had been assigned a descent to 3,000 ft
and was instructed to maintain the best approach speed. He had been
given traffic information on the Dash 8 and was expecting to be
instructed to sight and follow that aircraft. Use of the sight and
follow procedure by air traffic control (ATC) was common and
transferred separation responsibility from ATC to a pilot. The
Cessna pilot could see the Dash 8 ahead on final and continued
descent below 3,000 ft without a clearance. He later stated that he
only became aware that he had not complied with his clearance after
he transferred to the aerodrome control frequency. The pilot also
said that he believed there was no risk of collision.
The Approach One controller was an experienced controller and
was also a team leader. He was on the second shift of a four-day
cycle and had commenced the shift at 1100. He had worked the same
shift the previous day. The controller had two days off duty before
commencing this shift cycle. On the day of the occurrence he had
visited a relative in hospital at 0800 and then returned home to do
some paperwork before going to work. The relative had entered
hospital about a month previously and the controller had visited
regularly over that period. The controller was aware of the need to
not allow the relative's illness to impact on his work. He believed
he had achieved a balance between work and non-work
commitments.
The controller spoke briefly with the Approach Two controller
and gained the impression that the Cessna was under the control of
the Approach Two controller. Consequently, as he saw the distance
reducing between the Dash 8 and the Cessna he was waiting for a
response from the Approach Two controller despite the fact that
both pilots were operating on the Approach One radio frequency.
The Aerodrome controller was concerned with the reduction in
spacing between the aircraft, and asked the Approach One controller
to slow the Cessna to provide sufficient time for the Dash 8 to
vacate the runway. That prompted the controller to ask the pilot of
the Cessna if he could see the Dash 8. The pilot replied that he
could, and was then instructed to contact the Aerodrome controller,
who instructed the pilot to make an orbit, as there was
insufficient spacing to ensure that the runway standard would be
met.
