The Sydney approach radar controller was operating a combined
departures/approach service during the early morning shift when
staffing was minimal, and had been on duty since 0245.
For noise abatement reasons, runway 34 was the preferred runway
for arrivals prior to 0600, but was not utilised due to an
excessive downwind component. As a result, a number of inbound
aircraft were required to hold, in order to land on runway 16 after
0600. The approach controller was required to nominate to the
adjacent sector controllers the minimum longitudinal spacing
required between successive arriving aircraft. Local procedures
recommended a 15 NM spacing. The approach controller requested and
was provided with 10 NM longitudinal spacing between aircraft,
including a Boeing 747 (B747) approaching from the south-west,
which was sequenced to land ahead of a Boeing 767 (B767) arriving
from the north. The controller was also managing a number of other
arriving aircraft.
Independent visual approaches (IVAs) to runways 16L and 16R were
in use. The approach controller subsequently amended the initial
arrival sequence when it became apparent that the B767 would arrive
earlier than the B747. This placed those aircraft as number two
(runway 16L) and three (runway 16R) respectively in the arrival
sequence.
The crew of the B767 were vectored to intercept the runway 16L
localiser at approximately 30 NM, and instructed to report when
they had that runway in sight. The B747 crew had been instructed to
turn right onto a heading of 120 degrees in order to intercept the
runway 16R localiser. They were subsequently cleared to make a
visual approach after reporting that they had runway 16R in sight.
However, as the B747 turned onto final, the aircraft drifted to the
left through the centreline of the 16R approach path, triggering a
resolution advisory, from its traffic alert and collision avoidance
system (TCAS), for the crew to descend. The approach controller
observed the close proximity of the aircraft and issued
instructions to both crews to turn their respective aircraft from
final using a "breakout" procedure. The B767 was sighted by the
B747 crew as their aircraft passed through the final approach path.
The lateral distance between the aircraft was reduced to 0.3 NM at
a time when the vertical separation was 500 ft.
Normally, IVAs are conducted by a director controller using
specific procedures, which included the use of a 20 NM scale on the
radar display, and a map for intercept guidance. In this instance
the approach controller had his display set to a scale greater than
20 NM, and did not use the IVA map. Controllers are also required
to provide a radar vector not exceeding 30 degrees for intercept of
the localiser. The vector issued to the B747 crew provided a
36-degree intercept of the localiser. Moreover, crews subject to
IVA procedures are responsible for a number of actions detailed in
the Aeronautical Information Publication (ENR 1.1 - 48, paragraph
36.3.1) including, "ensuring that the runway centreline is not
crossed during intercept".
Just prior to the occurrence, two controllers arrived to
commence the morning shift from 0600. One of these would have
normally replaced the overnight controller; however, due to the
number of arriving aircraft, these controllers were instructed to
staff the director and flow control positions. A third controller
arrived and was waiting to take over from the approach controller
when the incident occurred. However, the approach controller's
workload prevented him from handing over responsibility for the
position at that time.
The approach controller limited his options by coordinating the
provision of a 10 NM spacing between successive arriving aircraft.
As a result, when the crew of the B747 allowed their aircraft to
pass through the extended centreline there was limited margin for
error, resulting in an immediate traffic confliction. The
performance of the controller was probably degraded by the effects
of fatigue and workload. The performance of the B747 crew was
likely to have been affected by similar factors.
The provision of additional staff prior to 0600 to provide
either a flow or director controller to assist the approach
controller, or to relieve the approach controller earlier, would
have reduced the approach controller's workload during a critical
period.
