Loss of separation

Sequence of events

The Short Bros SD 3-60-300 (Shorts) was being radar vectored by air traffic control for an instrument landing system (ILS) approach to runway 15 at Cairns.

The weather conditions were fluctuating about the landing minima with low cloud and rain passing through the local area in general "stream" conditions. The automatic terminal information service was quoting a cloud base of 1,000 ft with lower patches and visibility reduced to 5,000 m in passing showers. The conditions were observed to deteriorate during periods of heavy rain showers and the air traffic control tower staff updated each crew as appropriate.

As the Shorts intercepted the final approach path at 14 NM from touchdown, the aerodrome controller informed the approach controller that the weather had deteriorated at the aerodrome and that there was a likelihood that the Shorts would carry out a missed approach. The approach controller informed the crew and transferred them to the tower frequency so that the aerodrome controller could provide timely updates of the changing weather situation.

At 0744:05 Eastern Standard Time, the pilot of a Cessna 208 (Cessna) reported ready to depart on the aerodrome control frequency and was instructed to line-up. At that time, the Shorts was approximately 9 NM from touchdown with a ground speed of 120 kts.

The aerodrome controller received a departure instruction of "Left 360 unrestricted" from the approach controller (who was also providing the departure service). The pilot of the Cessna was then given a take-off clearance in accordance with that instruction but with an additional instruction to remain on the aerodrome controller's frequency when airborne. The aircraft commenced take off roll at approximately 0745:00; when the Shorts was approximately 7.5 NM from the runway 15 threshold.

At 0745:05, the crew of the Shorts was informed that the rain was increasing at the field and that the runway lights were on stage 6; the maximum intensity.

At 0746:04, the pilot of the Cessna was asked to expedite his climb through 2,000 ft and, at 0746:30, the crew of the Shorts was cleared to land.

At 0748:29, the pilot of the C208 apologised for the slow rate of climb and commented that he was "... just doing his best". At about the same time, the crew of the Shorts commenced a missed approach and, at 0748:39, they were instructed to maintain 1,500 ft and informed that there was "... traffic abeam you now at the 9 o'clock position". That transmission by the aerodrome controller was followed, at 0748:56, by a broadcast to the pilot of the Cessna saying "... caution traffic in the missed approach".

At 0749:07, the aerodrome controller updated the traffic information to the crew of the Shorts with "... caution, the traffic is in your 12 o'clock position at half a mile". The reply was garbled and included the statement "... we are maintaining one thousand at the moment..." which was followed by words that were not completely discernible but included "... one thousand five hundred..."

At 0749:27, the pilot of the Cessna was instructed to report leaving 1,500 ft and replied that he had left that altitude. A subsequent radar analysis indicated that the aircraft was climbing through 1,550 ft at that time.

At 0749:40, the approach controller checked with the aerodrome controller to ascertain his plan for separation. The reply was that there was "... not much to do". However, at 0749:51, the aerodrome controller broadcast to the crew of the Shorts that radar indicated traffic in the same position at the same level. The reply was that the crew had sighted the Cessna and were passing that aircraft.

Radar analysis indicated that the aircraft had passed at approximately 0749:50 with a minimum horizontal distance of about 70m and a vertical displacement of between 100 - 200 ft. The required separation standard was either 3 NM horizontally or 1,000ft vertically. There had been an infringement of separation standards.

Missed approach and departure procedures

Due to the constraints of terrain surrounding the Cairns aerodrome, both the missed approach and departure procedures required tracking in a 40 degree sector to the north-east. The missed approach required an initial climb straight ahead to the Middle Marker, then a climbing left turn onto a heading of 030 degrees to intercept the 045 radial of the Cairns VOR (Very High Frequency navigation aid), with a climb to 4,000 ft or a level assigned by air traffic control.

The standard instrument departure required a left turn at the earlier of 400 ft or the departure end of the runway, onto an assigned heading between 350 - 030 degrees. The lowest altitude for radar vectoring in this sector was between 1,000ft and 3,300ft depending on the precise position of the aircraft at the time.

This combination of tracking requirements resulted in a guaranteed tracking conflict whenever a missed approach was commenced when a departing aircraft was within 3NM of the aerodrome. Furthermore, an infringement of separation standards would occur whenever a missed approach was carried out in instrument meteorological conditions without vertical separation being established.

Separation standards

Air traffic controllers were limited to a minimum altitude of 1,500 ft for terrain clearance in the case of a missed approach. To establish the vertical separation standard of 1,000 ft (or 500 ft in an emergency), a departing aircraft would have to be at or above 2,500 ft (or 2,000 ft in an emergency). When the Shorts was established in the missed approach turn, it was climbing through 700 ft while the Cessna had left 1,300 ft.

The radar standard was not achieved as the tracks crossed each other approximately 2NM north-east of the runway. As the aircraft had to track in the same narrow sector of airspace, it would have been some minutes before a radar standard could be established.

Visual separation was not an option due to the prevailing weather conditions. The aerodrome controller could not see either aircraft as they came into conflict.

Lateral separation - the Manual of Air Traffic Services section 6-4-3 stated "lateral separation is considered to exist between an arriving aircraft that subsequently commenced final approach, and a departing aircraft that has been cleared on a segregated flight path". That is, a situation where the departing aircraft will not be manoeuvring within 45 degrees of the reciprocal of the final approach path while an aircraft is on the final approach path. The assigned heading of 360 degrees for the Cessna did not comply with that standard.

Longitudinal separation standards did not apply because they required distances greater than those required for radar standards.

Aircraft performance

The Shorts, a 36 passenger aircraft, had seven persons on board and very little freight. Consequently, when the missed approach was commenced, the crew attained a rate of climb of 700 - 800 ft/min. They stated that 300 - 600 ft/min was their expected rate of climb.

The Cessna was at maximum take-off weight and, because of the heavy rain, the pilot had selected the Inertial Separation Handle to bypass mode. That operation helped to divert heavy rain droplets around the engine so that the risk of flame-out was reduced.

When airborne, the pilot of the Cessna experienced severe turbulence and downdrafts, along with buffeting from the gusty wind and heavy rain. The combination of the prevailing weather conditions and the selection of bypass mode resulted in a degraded climb performance from that normally expected. Radar analysis indicated that the Cessna had an average rate of climb of 400 ft/min from take-off to the point of closest proximity and, at times, a rate of climb near zero. The pilot stated that he expected a rate of climb between 800 - 1,200 ft/min.

Air traffic control procedures

The Manual of Air Traffic Services (MATS) section 6-4-3 specified the procedures to be applied in the case of an arriving aircraft and an aircraft taking off. It stated that "a departing aircraft may be permitted to take off during the period before an arriving aircraft will commence its final approach" but goes on to say that such take-off clearance "... is conditional upon the application of separation after take-off is commenced".

Final approach was defined as 8NM from the runway 15 threshold. The aerodrome controller may have complied with the distance requirement as the Cessna was cleared for take-off when the Shorts was approximately 8NM from the threshold.

Cairns Local Instructions (TWR - 29) reinforced the provisions of MATS in the specific instance of the conflicting missed approach and departure headings from runway 15. They stated that "... consideration must be given to increase the cut-off distance used between the landing aircraft and the aircraft commencing take-off when weather conditions are such that visual or radar separation of the overshooting aircraft and departing aircraft cannot occur". Local Instructions did not specify clearly who had the responsibility for separating the missed approach from the departing aircraft. Approach control was responsible for the airspace but the aerodrome controller had to advise the approach controller of the most appropriate heading consistent with the ability to provide separation with other airborne traffic.

Cairns controllers operated in such a way that the aerodrome controller separated an aircraft on the missed approach path with other traffic, using visual separation until an alternative standard could be achieved. As the weather conditions precluded such an option, a specific alternative was required. Tower controllers were not rated to provide radar separation and could only use the radar display "for information". However, Local Instructions specified that it was the aerodrome controller's responsibility to ensure that radar separation existed between an aircraft on short final and not yet in sight and an aircraft becoming airborne.

MATS 6-5-1 allowed a tower controller to provide an uncoordinated radar vector to initiate separation in cases such as a missed approach. However, MATS required Local Instructions to specify the details. Cairns Local Instructions did not specify any such details.

Aerodrome controller

The controller had considered extending the cut-off distance but believed that, as the Shorts had not commenced final approach, he could safely clear the Cessna for take-off. He had witnessed numerous departures by Cessna 208 type aircraft and had an expectancy that the aircraft would climb at a rate which would enable vertical separation to be easily achieved if the Shorts commenced a missed approach. He also expected the Cessna to proceed at a speed that would position that aircraft well ahead of the Shorts at the crossing point of the departure track and the missed approach path.

Although the approach controller had nominal responsibility for the airspace, the aerodrome controller had assumed separation responsibility when he retained the pilot of the Cessna on his radio frequency for departure. As the Cessna departed, the controller observed that it did not turn in accordance with the standard instrument departure instructions but continued for approximately half a mile before commencing the turn. He then noticed that the rate of climb was not as good as he had expected and, at 0746:11, asked the pilot to expedite through 2,000 ft and report leaving 2,000 ft. That instruction was to maintain his traffic management plan of achieving vertical separation with any missed approach procedure and would have provided a 500 ft emergency standard if he maintained the Shorts at 1,500 ft in the missed approach.

As the aircraft closed to within 1.5 NM, the controller gave traffic information to both crews. However, that information did not include the aircraft type, or height, or relative height. The information was only position and distance to the crew of the Shorts and included the words "... traffic abeam you now at the 9 o'clock position". That information was incorrect as the Shorts was in a left turn and the traffic was actually in the 12 o'clock position moving towards the 2 o'clock position. The pilot of the Cessna was advised "Caution, traffic on the missed approach". The controller asked the other controllers in the tower at the time for advice but they were unable, in the time available, to offer an alternative course of action.

When the crew of the Shorts made a broadcast that they were "... maintaining 1,000 (feet) at the moment..." in the middle of a transmission that was broken and partly unintelligible, the controller neither questioned the crew as to their mention of the words "... one thousand five hundred..." during that broadcast nor did he issue an altitude instruction. However, he did obtain an altitude report from the pilot of the Cessna which indicated that the aircraft had left 1,500 ft on climb. The controller's subsequent conversation with the approach controller indicated that he was satisfied with the separation standard saying "...(the Shorts) supposed to be maintaining 1,000 (ft) the other has left 1,500 (ft) ...".

The controller was of the opinion that the altitude read outs from the Shorts were varying so much that he did not know that the aircraft had not maintained 1,000 ft. Radar analysis of the readouts indicated a relatively steady increase in height over the 90 seconds from 0748:30 - 0750:00 but with two "spikes" at approximately 1,100 ft (at approximately time 0749:07) and 1,500 ft (at approximately time 0749:45).

Approach controller

The approach controller had issued the departure instruction for the Cessna believing that, as the Shorts was about 8NM from touchdown, the aerodrome controller would not depart that aircraft until after the arrival, or that the Shorts was in sight and reasonably assured of a landing. However, the terminology used by the aerodrome controller "next CYC" indicated that the Cessna would commence take off within 1 minute of the receipt of a departure instruction.

As the situation developed, the controller monitored the radio frequency of the aerodrome controller to observe the plan for separation. He had heard the requirement to remain with the tower given to the pilot of the Cessna and considered that the aerodrome controller had accepted the responsibility for separation with this action. As the radar display indicated that the aircraft were on conflicting tracks and at similar altitudes, other controllers asked what separation was being applied. The approach controller replied that the aerodrome controller was providing the separation but elected to prompt the tower with the question "you right?". This coordination occurred at 0749:40, approximately 10 seconds before the point of closest proximity, and was the first contact between the controllers since the departure instruction for the Cessna was issued.

Emergency training

The Cairns air traffic controllers had not received regular training in emergency or unusual situations. Tower controllers had last undertaken formal refresher training in October 1997. However, the aerodrome controller had been absent on recreational leave and did not attend the training. He had received formal tuition in dealing with similar circumstances during his aerodrome control training in December 1997 and January 1998.

The aerodrome controller stated that he had experienced only one missed approach due to poor weather in his 3 years at Cairns. As the incident developed, he asked for advice from his fellow tower controllers but as they were occupied with their own tasks, they were unable to give a properly considered response.

Pilot of the Cessna

The pilot was conducting a single pilot operation and had intended to comply with the requirements of the standard instrument departure by turning left at 400 ft or the departure end of the runway. However, when airborne, the initial climb did not proceed as well as expected, with severe turbulence and heavy rain buffeting the aircraft. The airspeed was not increasing as quickly as he would have liked and at the upwind end of the runway the aircraft had only reached an altitude of 200 - 250 ft. Consequently, the pilot elected to continue on runway heading until a more stable climb was achieved. The left turn was commenced at an altitude of 300 ft and an indicated airspeed of approximately 70 kts. There was no broadcast to air traffic control indicating the variation to the standard procedure.

Once the aircraft had turned onto the assigned heading of 360 degrees, the pilot made every effort to maximise the rate of climb but was limited by the aircraft performance in turbulent weather conditions. At 0748:29, he broadcast to the aerodrome controller that he was experiencing a slower than normal rate of climb.

When, at 0748:56, he was given conflicting traffic information, he attempted to sight the other aircraft but found visibility limited in cloud and heavy rain. Shortly after, the aircraft broke into a small clear patch and the pilot saw the Shorts just below and marginally to his left. He estimated that the aircraft would pass just behind his own and elected not to take any evasive action.

Crew of the Shorts

The co-pilot was the flying pilot and, as the aircraft approached the minima, the crew found themselves in cloud, heavy rain and subjected to severe turbulence culminating in their decision to commence a missed approach.

The crew's main preoccupation was to ensure the safe climb-out of their aircraft in the left turn required by the procedure and, as they were experiencing instrument meteorological conditions, their first priority was to fly the aircraft. Consequently, they did not immediately inform air traffic control of their commencing a missed approach. Before they could broadcast any details, the aerodrome controller issued an instruction for them to maintain 1,500 ft and passed traffic information. As they were still in cloud and rain, their lookout was both occasional and of limited effect.

A short time later, the controller issued an updated traffic alert indicating that the other aircraft was half a mile ahead. The response from the pilot in command was that they were maintaining 1,000 ft temporarily but still climbing to 1,500 ft as cleared by air traffic control. The pilot in command had intended to maintain 1,000 ft after the traffic information had been passed but the co-pilot did not hear the instruction as it was said during the radio broadcast to air traffic control and during a period of intense flying activity. As the pilot in command was about to reiterate the maintain 1,000 ft instruction to the co-pilot, the aircraft broke into the same clear patch as the Cessna and they saw that aircraft ahead and slightly above. The co-pilot levelled the aircraft momentarily to ensure that they would pass beneath the Cessna and then continued the climb to 1,500 ft when established clear of it.

A Fokker 50 was conducting a practice Instrument Landing System (ILS) approach for runway 24 at Perth, with an intended overshoot to Cunderin. A Cessna 172 was tracking via Northam to Perth with an intended overshoot to Jandakot. Other traffic in the area at the time was a helicopter tracking from Perth to Mundijong.

At 1133 Western Standard Time the crew of the Fokker was conducting the overshoot onto a radar heading which placed the aircraft in close proximity to the Cessna. The pilot of the Cessna sighted the Fokker and turned and descended to avoid that aircraft.

Perth Air Traffic Control had two runway specific traffic management plans. These were North-East (duty runways 03/06) and South-West (duty runways 21/24). Airspace ownership changed dependent on the plan in use and the airspace was divided as Terminal Control Area South (TMA S) and Terminal Control Area North (TMA N), the division occurring along the 281/077 radials from the Perth VOR. At the time of the occurrence the plan placed North-East and TMA S under the control of approach (APP) and TMA N under the control of departures (DEP).

The Perth Aerodrome Controller (ADC) had assumed responsibility for the Aerodrome control position approximately 10 minutes prior to the occurrence. The departure controller had received a handover 10 minutes prior to the incident and was unaware that the Fokker would turn back towards the Cessna.

The relative positions and intended tracks of both the Fokker and the Cessna were such that the departure controller was required to maintain vertical separation until within approximately 5 NM of the aerodrome, with the Fokker passing under the Cessna near Parkerville.

The aerodrome controller coordinated with the approach controller for departure instructions for the helicopter. The approach controller issued the instruction "right unrestricted you separate all the inbounds". The aerodrome controller accepted this and the instructions were issued without reference to the departure controller. The aerodrome controller subsequently coordinated with the approach controller for the overshoot instructions for the Fokker. The approach controller issued the instruction "left 120 unrestricted", but shortly after revised the instruction to, "separate with the helicopter, or keep him on runway heading for a bit to get him above". The aerodrome controller advised that the left turn onto a heading of 120 degrees would suffice. The approach controller issued the overshoot instruction without reference to the departure controller.

Coordination between the tower controllers and the Terminal Control Area controllers utilises the Operational Data Information contained within the radar label display. Coordination between approach and departures is via hotline communications.

Temporary Local Instruction (TLI) SDW/98/160 page 47 Section 5 paragraph 12.3 provides a choice of units to coordinate for aircraft overshooting Perth with the proviso "as appropriate." That section was contained in a letter of agreement between the Tower and Terminal Control Area and specifically dealt with overshooting aircraft.

The same TLI at page 65 Section 6 paragraph 2.1.1 advised that "In all instances the next call must be to DEP". This instruction was headed "Management of Departing IFR Aircraft-Perth" and dealt with Perth Departures from the non-duty runway. That paragraph specifically required the aerodrome controller to coordinate with the departures controller for departure instructions on aircraft departing from the non-duty runway but did not mention the procedure to be followed for overshooting aircraft from the non-duty runway.

The aerodrome circuit was active with a number of aircraft conducting circuit training, or inbound for landing. Both runways 35 and 30 were in use. Runway 30 intersected runway 35 approximately 750 m from its threshold. The tower was staffed with three controllers operating the aerodrome control (ADC), coordination and surface movement control positions.

The ADC had instructed the crew of a De Havilland Dash 8 (Dash 8) to line up for a departure from runway 35. The pilot of an American Aircraft Corporation Cheetah (Cheetah) had been instructed to continue approach for runway 30. The ADC cleared the Dash 8 crew for take-off and then looked towards the final approach path for runway 30 to monitor the approach of the Cheetah. As the ADC completed the transmission to the Dash 8 crew, he saw that the Cheetah was on short final and immediately transmitted an instruction to the Dash 8 crew to hold their position. This instruction was over-transmitted by the acknowledgment of the take-off clearance by the pilot in command of the Dash 8. The ADC commenced to issue a land-and-hold-short instruction to the pilot of the Cheetah; however, seeing that the Dash 8 was starting its take-off roll, he ceased the transmission and issued a further instruction to the Dash 8 crew to hold position. This instruction was over-transmitted by the Cheetah pilot reporting that he was initiating a go-around. The Dash 8 became airborne prior to the intersection of the runways, however, the crew held their aircraft at approximately 50 ft above ground level while the Cheetah passed approximately 100 ft above and slightly behind the Dash 8.

The automatic voice recording of the radio transmissions from the ADC during this period indicated that there were few or no intervals between any of his transmissions. The pilot of another aircraft that was operating in the circuit heard the hold-short instruction. The crew of the Dash 8 reported that they did not hear either of the hold-short instructions.

The ADC had formulated a traffic plan but this changed when a turbojet aircraft he thought was going to conduct a full-stop landing on runway 35, conducted a touch-and-go. The ADC had instructed the crew of the Dash 8 to line up on runway 35 after the approach of the turbojet aircraft, and had amended the approach of the Cheetah to runway 30 to facilitate the departure of the Dash 8. The ADC did not instruct the pilot of the Cheetah to report at a position that would have enabled him to adjust the traffic sequence if required. There was also a delay between the time the ADC approved the Dash 8 crew to line up, and the eventual issue of the departure instructions and a clearance. This delay was due to radio transmissions from the pilot of the turbojet aircraft, as well as the coordination of inbound traffic with the approach controller. During this period, the Cheetah pilot had continued his approach to runway 30. The ADC did not check the position of the Cheetah in relation to the intersection of the runways prior to issuing the take-off clearance to the Dash 8 crew. That was done as he was completing the transmission of the take-off clearance to the crew. As a final action to resolve the conflict between the aircraft, the ADC proposed to issue a land-and-hold-short instruction to the pilot of the Cheetah; however, the landing distance available (590 m) to the pilot did not meet the distance required (900 m) for land-and-hold-short operations.

The Manual of Air Traffic Services details the radiotelephony phraseology (RTF) to be used by controllers to cancel take-off clearances or to stop a take-off in emergency conditions. The ADC used only part of the required RTF for the cancellation of the take-off clearance. He did not use the RTF for an emergency situation.

A Boeing 737 (B737), VH-TJT, was en route from Darwin to Adelaide via air route J187 at flight level (FL) 370. Another B737, VH-CZN, was en route from Ayers Rock to Sydney via air route G222, also at FL370, which was a standard level for the direction being flown by both aircraft. The air routes converged, and eventually crossed at Oodnadatta. Both aircraft were under procedural (non-radar) control by Melbourne Sector 1. The sector console was staffed by a controller who was undergoing re-familiarisation prior to being checked for return to controlling. He was being supervised by a controller who had recently returned after a six month break from full-time operational controlling.

The controller had calculated estimates for Oodnadatta of 1518 and 1520 respectively for CZN and TJT. At 1515, when the crew of TJT reported at SARAH, 40 NM north-north-west of Oodnadatta, the controller became aware that there was no separation standard being applied between the two aircraft, so he instructed the crew of TJT to descend immediately to FL350. The crew reported on descent and indicated that their traffic alerting and collision avoidance system (TCAS) showed an aircraft 33 NM ahead, over Oodnadatta. The crew of TJT subsequently reported maintaining FL350 at 1520. As a result, there was a breakdown of the required vertical separation standard of 2,000 ft.

Both controllers had earlier noted the possibility for conflict between the two aircraft and annotated their respective flight progress strips with an Oodnadatta position, and the calculated estimates for that position. The estimates were annotated at different locations on the strips. There was no local instruction for the standardisation of the annotation of the Oodnadatta position or similar positions that marked the intersections of the various route crossings in the area. During the following 90 minutes, the traffic level steadily increased and the two controllers had discussed the need for a coordinator. The sector was normally operated as a solo operator position; however, there were periods when there were significant or complex traffic levels and there were procedures to enable the controller to be assisted by a coordinator in such cases.

Approximately 10 minutes prior to the occurrence, the controllers requested the assistance of a coordinator and as a consequence, a third controller joined them at the console. At this stage, the traffic situation was very busy, with approximately 70 flight progress strips being monitored and with additional strips being discarded or added to the board as flights progressed through the sector. The coordinator controller had little opportunity to obtain an adequate handover/takeover brief from the two controllers already at the position. The third controller assumed the coordinator position and endeavoured to action any items that he considered required attention as he attempted to gain some idea of the traffic disposition. He was unable to monitor the Sector 1 controller's air-ground-air program on a continuous basis due to the conduct of coordination actions. The work at the console was difficult, with three controllers working in an area normally used by only two controllers.

As a result of a combination a factors, the potential confliction between CZN and TJT, although recognised earlier by both controllers, was subsequently overlooked as the sector workload increased. It was only when the crew of TJT reported at SARAH that action was undertaken resolve the situation.

Airservices Australia carried out an investigation of this occurrence under the overall supervision of a Bureau officer. The significant factors that contributed to this occurrence were found to be;

1. The two controllers manning the Sector 1 position were not operating at their optimum level of performance due to a lack of recency.
2. Following an increase in Sector 1 traffic density, the controllers' recognition that they required coordination assistance to manage the increased workload was too late to provide any effective relief.
3. The amount and disposition of traffic in the sector led the controllers to be distracted to a point where they were unable to adequately monitor all sector traffic.
4. The controllers' annotation of flight progress strips did not alert them to the possibility for a conflict between CZN and TJT.

A Boeing 747 (B747) was en route from Auckland to Melbourne, maintaining flight level (FL) 330. The aircraft was experiencing some turbulence. The crew were communicating with Auckland air traffic control via controller pilot data link communications (CPDLC) and were awaiting a response to a request to climb to FL350.

The crew had observed on their traffic alerting and collision avoidance system (TCAS) that another aircraft was crossing their route from the south-east to the north-west at FL350. They were aware that a clearance to climb to FL350 would not be available until that aircraft had passed. The other aircraft was a B737 en route from Wellington to Brisbane. The air routes intersected at the VIMAV reporting point. At 2002 the B737 crew reported at VIMAV maintaining FL350. At 2005, the B747 passed VIMAV.

At about 2010, the B747 crew received a conditional clearance to climb to FL350 at 2018. The delay in the climb approval was required to establish a 15-minute time standard between the two aircraft at the intersection of the air routes. The B747 crew immediately commenced climb to FL350 after the message was received. At 2012 they dispatched a message reporting they were maintaining FL350. When air traffic control notified the crew via high-frequency radio that they had not complied with the clearance, the crew descended the B747 to FL330. The B747 TCAS did not register an alert during the period that separation was infringed.

Normal company CPDLC practice for the B747 crew was for the non-flying pilot to read out the message on the screen, and for this to be confirmed by the flying pilot. Once the message and the subsequent response were confirmed by the two crew members the non-flying pilot dispatched the message to air traffic control.

The investigation found that the crew, for reasons unknown, had mis-interpreted the datalink message as an immediate clearance to climb. It is possible that, due to the turbulence being experienced, the crew acted hastily to acknowledge the message and climb the aircraft to reduce passenger discomfort. It is likely that either one or both of the crew were not as vigilant in their checking of the message as they would have been under less demanding circumstances.

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.