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.