Boeing 737-377, VH-CZO

The aerodrome controller cleared VH-CZO for a night-time take-off from the Brisbane runway 01, believing that VH-OGG, after landing, had vacated the runway onto the high-speed taxiway A4S. At the time, CZO was at the A7 holding point. The crew of OGG alerted the controller (and the crew of CZO) that they were on the active runway. Shortly after, the controller asked the crew to confirm that they were on taxiway A4S and was advised that they were not. Aware that CZO had not lined up on the runway, the controller did not cancel the take-off clearance, but monitored the situation until OGG vacated the runway at taxiway A4.

The high-speed taxiway A4S was 1,900 m from the runway 01 threshold, and taxiway A4 was 2,310 m from the 01 threshold. Taxiway A4 required that the crew turn the aircraft through 90 degrees to exit the runway.

Taxiway A4S was equipped with uni-directional centreline lighting, which was not visible from the control tower. This made it difficult in conditions of reduced visibility for controllers to determine that an aircraft had vacated the runway and was on the high-speed taxiway. However, in visual meteorological conditions at night, it was not normal practice for controllers to ask crews to report when their aircraft was clear of the runway.

The Manual of Air Traffic Services (MATS) 6-3-1 paragraph 2 stated:

"When take-off or landing separation is based on the position of the preceding landing or taxiing aircraft and visual determination, particularly at night or in reduced visibility, is limited by poor azimuth resolution or other factors, the pilot of that aircraft shall be instructed to report when the aircraft has:

crossed and is clear of a runway intersection; or

stopped short of a runway strip; or

vacated the runway."

The MATS 6-2-3, paragraph 31 stated:

"Before clearing an aircraft for take-off, and immediately before take-off is commenced, the tower controller shall make a visual check from the control tower to determine as far as practicable, that the take-off path is not obstructed. If the take-off path is obstructed, take-off clearance shall be withheld or cancelled as appropriate, until the obstruction no longer exists."

The prescribed separation standard was detailed in MATS 6-3-4 paragraph 24. The standard required that a departing aircraft shall not be permitted to commence take-off until the landing aircraft has vacated and is taxiing away from the runway.

The controller cleared CZO for take-off using the provisions of MATS 6-2-3 paragraph 32. This paragraph stated:

"Take-off clearance need not be withheld until prescribed separation exists if, in the opinion of the controller, no collision risk exists and there is reasonable assurance that separation will exist when the aircraft commences take-off roll."

The difficulty in accurately locating aircraft on the high-speed taxiway A4S at night from the control tower is evidenced by the controller twice assuming that OGG had departed the runway and entered the taxiway. The awareness among local controllers of this difficulty should have encouraged the use of procedures to ensure the maintenance of required standards. However, the controller only recognised that his visual assessment was incorrect when advised by the crew of OGG. It is likely that the controller subsequently assessed that as CZO had not lined up, it was not necessary to cancel the clearance, but the two aircraft should simply be monitored.

The procedures relating to take-off clearances permitted a degree of discretion by the controller. However, that discretion was conditional upon a valid determination of collision risk and the maintenance of separation standards. Consequently, MATS 6-2-3 paragraph 32 was not appropriate to the issuing of the take-off clearance, as the controller had not positively identified the relative positions of the aircraft.

The controller did not withhold the take-off clearance for CZO when there was no reasonable assurance that separation would exist between the aircraft when CZO commenced the take-off roll.
The lack of visibility of the A4S taxiway at night from the control tower required that aerodrome controllers instruct pilots to confirm when clear of the runway.

As a result of this occurrence, the Bureau of Air Safety Investigation is currently investigating two safety deficiencies. The first relates to the inappropriate use of MATS 6-2-3 paragraph 32 by aerodrome controllers. The second relates to the non-application of MATS 6-3-1 paragraph 2 by controllers employed in the Brisbane aerodrome control tower.

Any safety output issued as a result of these analyses will be published in the Bureau's Quarterly Safety Deficiency Report.