A Boeing 747 (B747) was on an international flight from Sydney to Los Angeles, maintaining flight level (FL) 290. The flight was operating in controlled airspace and was being managed by the Brisbane Sector 8 air traffic controller, using procedural control methods. The flight crew and controller were communicating via controller-pilot data link communications (CPDLC). The crew requested approval to climb to and operate between FL290 and FL330. The controller sent an approval at 0659 on the CPDLC for the crew to climb to the block level. Prior to changing levels, the crew received traffic information on their aircraft traffic alerting and collision avoidance system (TCAS) display. The traffic was approaching from the opposite direction, 2,000 ft above the B747. The B747 crew maintained their aircraft at FL290 and immediately reported via the CPDLC that they were unable to comply due to traffic. This message was sent at 0659 but was not received at the controller's terminal until 0706. The delay was believed to be due to network lag. The traffic was subsequently identified as a British Aerospace 146 (BAe 146), en route from Norfolk Island to Sydney at FL310.

The controller had assumed responsibility for the sector following a handover/takeover a few minutes after the request from the B747 crew, to operate in the block level, had been received. The previous sector controller had coordinated the use of the block level with adjacent sectors in anticipation of approving the request, after establishing that the two aircraft had passed each other. Neither controller had calculated an estimated time of passing (ETP) for the aircraft. An ETP of 0659 was subsequently calculated after the occurrence. Air traffic control standards require that aircraft travelling in the opposite direction on the same route cannot climb or descend through the level of the other aircraft during a specific period before and after the ETP. In this case, the appropriate time standard was 10 minutes. Consequently, the controller should only have approved the use of the block level after 0709.

The controller taking over responsibility for the sector stated that he was aware of the confliction and had prepared the message approving the use of the block level, with the intention of holding it in the CPDLC terminal until after the aircraft had passed each other. The CPDLC did not have a hold function in the "reply" mode in which it was operating. Consequently, the message was ready for dispatch. The "send" function on the terminal was actioned by selecting an icon and activating this via a computer "mouse" button. The controller's response to the initial request should have been either to acknowledge receipt with "standby" or "request deferred". This would have then enabled the controller to respond further to the message after establishing a passing standard. The controller awaited an audio response from the terminal to indicate that the message was being held. When this did not occur, he prepared and sent a message to the crew instructing them to maintain FL290. The crew responded to this instruction with "Wilco". This response was received at the controller's terminal at 0701. The controller could have also used Flight Service high frequency (HF) radio communications as an alternative to the CPDLC, in order to instruct the crew to maintain FL290. Delays of up to 5 minutes were common when using the data link system.

The crew of a Metroliner, VH-WBA, had flight-planned from Plutonic Mine in Western Australia to Perth. On first contact with Perth Tower, the crew were instructed to continue the approach for sequencing with VH-EAM, which was to land on the crossing runway 24. After EAM had landed and was clear of runway 03/21, the aerodrome controller noted that his 'runway designator' strip had 'Tractor' written on the runway 03/21 section. He observed the tractor to be clear, scanned the runway and, when WBA was 5-6 NM from touchdown, cleared the aircraft to land on runway 21.

At the time the landing clearance was issued, Car 23 was parked on the runway, approximately 200 m from the southern end. The surface movement controller reacted by instructing Car 23 to 'vacate 21 immediately'. Using binoculars, the controller observed the technician throwing tools and equipment into the back of the vehicle. The controller assessed that Car 23 would not vacate runway 21 prior to WBA crossing the runway threshold, and advised the aerodrome controller. The aerodrome controller then directed that the aircraft go around, advising the crew that a vehicle was on the runway. The pilot in command estimated that WBA was at about 400-500 ft when they were instructed to go around and both pilots looked for, but did not sight, the vehicle on the runway.

The surface movement controller was in radio communication with four vehicles. Car 23, a white vehicle equipped with a flashing yellow light, had been on and off runway 21, conducting instrument landing system checks. Tender 1 was being repositioned across the airfield and two tractors were engaged in mowing near the threshold of runway 21. Shortly before the incident, both tractors were clear of the threshold area and Car 23 requested approval to enter the runway for the fourth time. Once on the runway, Car 23 required a 1-minute recall to allow for the clearing of tools and equipment. The surface movement controller noted that no aircraft were due immediately and checked with the aerodrome controller for a clearance for Car 23 to re-enter runway 21. The aerodrome controller approved the clearance, but did not change the 'runway designator' strip notation to indicate that runway 21 was now obstructed by Car 23. The surface movement controller then cleared Car 23 to enter the runway.

The procedures in use at the time required that an individual clearance be obtained each time a vehicle entered or crossed a runway. As a memory prompt, both the aerodrome controller and the surface movement controller utilised red flight progress strips engraved with the words 'runway obstructed'. The aerodrome controller would place the strip above the 'taxiing aircraft' bay on the console. In addition, the aerodrome controller used a red 'runway designator' strip which was divided into three sections indicating the runways 03/21, 06/24 and 11/29.

When a vehicle was cleared onto the runway, the 'runway designator' strip was moved into the console's 'active runway' bay. The vehicle's callsign would then be written in the section that designated the obstructed runway. The annotation of the 'runway designator' strip with vehicle callsigns was not a requirement of the Local Instructions, but was a normal practice of the aerodrome controller.

The use of the flight progress strip was intended to assist the controller's situational awareness in two ways: (1) the action in placing the strip in the appropriate console bay (setting the memory prompt) should have assisted in consolidating a strong memory trace, and (2) the strip could be checked at any time should the controller be unsure as to the status of the item or condition referred to. The use of the 'runway designator' strip with the vehicle callsign notated provided an additional memory prompt.

Four air traffic controllers were rostered for duty in the control tower at the time of the incident. In addition to the aerodrome controller and the surface movement controller, the team leader was in the Airways Clearance Delivery position and a fourth controller was performing administrative duties. The Coordinator position was not occupied because the team leader considered that the traffic was light. Each controller was appropriately trained and rated in their operating position. All were extensively experienced in tower operations at Perth. The controllers had earlier completed a busy traffic sequence and were in a lull between sequences at the time of the occurrence.

After landing on runway 27 at Melbourne during land and hold short operations, VH-CZH, a Boeing 737, vacated the runway via the parallel taxiway Echo which crossed runway 34 at a distance of 2,333 m from the threshold. The surface movement controller instructed the crew to hold short of runway 34 because VH-OGK, a Boeing 767, was landing.

VH-EAL, a Boeing 767, was taxiing for a runway 34 intersection departure at taxiway Juliet, 773 m from the runway 34 threshold. The co-pilot was the flying pilot. OGK had just landed on runway 34 and was vacating at the high-speed taxiway Foxtrot, 1,588 m from the runway 34 threshold. The aerodrome controller instructed the crew of EAL to line up and wait.

EAL's crew had noted VH-NKN, a Beech 1900, on final approach for runway 27. When OGK was clear of runway 34, the aerodrome controller cleared EAL for an immediate take-off. NKN was on a practice instrument landing system approach to runway 27 and was approximately at the outer marker. The aerodrome controller requested the crew of NKN to reduce to minimum approach speed.

The pilot in command of CZH reported that he saw OGK vacate runway 34 at taxiway Foxtrot and then received a clearance to cross runway 34. As CZH began to cross the runway, the crew observed EAL lining up with its landing lights on. At about one-half to two-thirds of the way across runway 34, the co-pilot of CZH commented to the pilot in command that it looked like EAL had started to roll for take-off. The pilot in command confirmed this and both pilots monitored EAL's progress. The forward section of CZH was well clear of the runway but the rear section was believed to be obstructing the runway when the crew noticed that EAL's take-off had been rejected. Both pilots observed the spoilers of the B767 extend.

At the time EAL was cleared for immediate take-off, its crew was not aware that CZH was crossing 34 at taxiway Echo. As they started to roll, the pilot in command saw that CZH had crossed about two-thirds of the width of the runway and estimated it would be well clear and so continued with the take-off. When the aircraft was at about 90 kts, the pilot-in-command heard the instruction "stop immediately" transmitted twice, took control from the co-pilot, applied reverse thrust and slowed the aircraft before exiting runway 34 at taxiway Foxtrot.

The controllers

The aerodrome controller was undergoing re-familiarisation training under the supervision of a rated training officer. Both controllers had extensive aerodrome control experience. The surface movement controller had worked at Melbourne tower since April 1998 and was a rated surface movement controller. He was not trained in aerodrome control at Melbourne.

The traffic management plan and outcome

The aerodrome controller had planned for CZH to cross runway 34 after OGK had turned to exit runway 34 via taxiway Foxtrot. A conditional clearance was issued to the surface movement controller to this effect. The conditional clearance was "after Qantas 33 has vacated the runway, cross runway 34", which was acknowledged by the surface movement controller. The training officer said that he was not aware of the interchange. The aerodrome controller's plan, which was endorsed by the training officer was to hold EAL in the lined-up position on runway 34 while CZH crossed the runway and while NKN landed on runway 27.

Although the training officer had endorsed the plan, the speed of NKN on final for runway 27 was erratic and as a result, his mental model changed. He perceived that there was an opportunity for EAL to take off before NKN landed. The training officer considered that the new plan was desirable because another aircraft was on long final for runway 34 and there was a possibility that it would have to go-around behind, or over EAL. The training officer reported that he did not think that the aerodrome controller had noticed the performance of NKN on final, which meant that the opportunity for it to land and the plan to work was diminishing.

The training officer conveyed the new plan to the aerodrome controller, who then cleared EAL for an immediate take-off. The aerodrome controller scanned the runway and noticed CZH crossing at taxiway Echo. The training officer reported that he was not aware that CZH had been cleared to cross runway 34 until after the take-off clearance was issued to the crew of EAL. The controllers both reported that they did not immediately cancel the take-off clearance issued to EAL because they assessed that CZH would be clear of the runway before EAL commenced the take-off roll. The rationale for this decision was based on their interpretation of Chapter 6 of the Manual of Air Traffic Services.

The aerodrome controller monitored the position of NKN, which was "getting close". He did not feel comfortable with the developing situation and instructed EAL to cancel departure. This transmission was made 21 seconds after clearing EAL to take-off. EAL started to roll and the aerodrome controller transmitted "EAL, stop immediately". When EAL continued to accelerate, the aerodrome controller transmitted again "EAL, stop immediately, stop immediately." The crew acknowledged this transmission, applied reverse thrust and slowed before exiting the runway at taxiway Foxtrot. The controllers both reported that the motivator for the cancellation of the take-off clearance was the potential for EAL to conflict with NKN on final to runway 27, rather than the potential for EAL to conflict with CZH, which was crossing on runway 34.

ATS procedures

The Manual of Air Traffic Services includes instructions for the control of departing and arriving aircraft within the traffic circuit and on the movement area of an aerodrome. Chapters 6 and 12 were relevant to this occurrence scenario.

The crew of a Boeing 737 (B737) was cleared by the Adelaide surface movement controller (SMC) to taxi to the Foxtrot 5 holding point for runway 05, and to cross runway 30. Earlier, the SMC had been issued with a blanket clearance by the aerodrome controller (ADC) that allowed aircraft to occupy or cross runway 30 without a specific clearance from the ADC. The use of a blanket clearance reduced the need for segmented taxi clearances.

There were three personnel rostered for duty in the control tower; an ADC, a SMC and a tower coordinator. At the time of this occurrence the tower coordinator was absent from the tower cabin, reducing the monitoring potential of tower staff. All staff were appropriately trained and rated.

While the SMC was issuing the taxi clearance to the crew of the B737, the ADC was arranging departure instructions for a Pilatus PC12 from runway 30. The ADC subsequently cleared the Pilatus to take off from runway 30, without first cancelling the blanket taxi clearance and resuming control of the runway. Shortly after issuing the take-off clearance, the ADC became involved in communications with the approach controller regarding other inbound aircraft. The SMC was occupied with other data processing duties.

The crew of the B737 had sighted the Pilatus in the lined-up position on runway 30, but was unaware that a take-off clearance had been issued to that aircraft. As the B737 approached the crossing point of runway 30 on taxiway Foxtrot 2, the crew saw the Pilatus commence to take-off. They applied heavy braking and stopped their aircraft with the nosewheel 1-2 m beyond the runway holding point. The Pilatus continued its take-off run. The crew of the B737 subsequently confirmed with the SMC that they had been cleared to cross runway 30.

The local procedures in the Adelaide tower for a blanket clearance of a runway release required the use of a bright yellow coloured flight progress strip with the words "RUNWAY 12/30 OCCUPIED". Although a strip was correctly placed in each of the strip presentation bays in front of both the SMC and the ADC to indicate that a blanket clearance was issued, that procedure failed to attract the attention of the ADC.

The investigation of this occurrence was carried out by Airservices Australia, monitored by a Bureau investigator. A number of significant factors were identified.

Air traffic control had issued the crew of a foreign Boeing 767 (B767) with an instruction to hold at Bindook. Although the published holding procedure required a left pattern, the crew turned the aircraft for a right pattern. The right turn subsequently placed the aircraft into conflict with a Boeing 747, which was being radar vectored to the south of Bindook. Separation was reduced to approximately 700 ft vertically, and 4 NM laterally. The required separation standard was 1,000 ft, or 5 NM.

An investigation revealed that the crew did not locate the holding pattern on the Jeppesen terminal chart. The depiction of the holding pattern was difficult to distinguish from other markings on the chart and the pattern was not displayed on the appropriate Standard Arrival Route (STAR) chart. In addition, the holding pattern was not loaded in the aircraft's flight management computer database. The Captain of the B767 reported that in the USA, where a holding pattern is not displayed, or in the absence of other information, a "default" right hand pattern is to be flown. There is no such procedure in Australia. As a result, the Captain elected to fly a right hand pattern without checking with air traffic control for holding pattern information.

The crew of a Metro 23 was cleared by the surface movement controller (SMC) at Perth to enter runway 11 and taxi to the threshold of runway 21 prior to departure. However, as the aircraft approached the runway 11 holding point, the crew checked the final approach path and saw a Cessna C402 landing on runway 11 in front of them.

A subsequent investigation revealed that the SMC had previously been using runway 11/29 as a taxiway for vehicle and aircraft movements. The procedure for release of the runway from the aerodrome controller (ADC) to the SMC was for both the ADC and SMC to de-select their respective runway 11/29 selection buttons. Both buttons would become illuminated when selected on, indicating that the runway was active. De-selecting each button had the reverse effect. Should the button be selected or de-selected on one side only, both lights would flash to alert the controllers to a mismatch.

In addition to the use of the runway selection buttons, both controllers were to coordinate off-line with each other using the phrase "runway 11/29 released to you" or "runway 11 active" as appropriate. Any traffic that might be on the runway would also be coordinated. Those procedures were detailed in the Perth Tower Local Instructions.

Just prior to the incident, the SMC had control authority for runway 11/29, and the runway 11/29 selector buttons were in the de-selected position. When the crew of the Metro requested a taxi clearance, the SMC cleared them to taxi to runway 21, entering runway 11 at taxiway Echo. The threshold of runway 21 is at the midway point of runway 11/29 and access to the threshold of runway 21 was achieved by taxiing via runway 11. Once details of the Metro were no longer required by the SMC, the flight progress strip for the aircraft was placed into the top transfer slot on the ADC's side of the console. This procedure was also documented in Perth Tower Local Instructions.

Three minutes after the taxi clearance was issued, the ADC elected to land a C402 on runway 11. Prior to issuing the landing clearance, the ADC selected the runway 11/29 selector button to indicate to the SMC that the ADC was taking control authority for runway 11/29. Because the SMC no longer held a flight progress strip as a memory marker, he also turned on his selector button and advised the ADC "no traffic runway 11". The ADC did not notice the Metro, which had not yet entered taxiway Echo, nor did he notice the flight progress strip in the top transfer slot. The ADC subsequently cleared the C402 to land on runway 11.