Loss of separation

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.

VH-CZA, a Boeing 737, was inbound to Brisbane and was being sequenced to follow VH-EWM, a BAe 146, for a visual approach to runway 19 via left base. Both aircraft were under the control of the Brisbane Approach radar controller and were being processed via the Coolangatta One Standard Terminal Arrival (STAR). VH-TNU, a Dash 8, was behind CZA and was being processed via the Jacob's Well Four STAR.

The Brisbane Flow Controller had originally assigned TNU to land on runway 14. This required the controller to position the aircraft east of the Jacob's Well - Brisbane track, and for the crew to track direct to the Brisbane Control Tower before joining right base for runway 14. There were two light aircraft operating to the south and southeast of the aerodrome at 1,500 ft on traffic survey work. The controller assessed that these aircraft may have conflicted with TNU overflying the aerodrome for runway 14. As well, there was departing traffic that he considered might also have conflicted with TNU being processed for runway 14. As a result, the controller decided to process TNU for runway 19.

The controller vectored TNU north to a position approximately abeam and above CZA and informed the crew that they were following the traffic which was low and to their right. The crew of TNU advised that they were still in cloud. At this time, TNU was approaching 5,000 ft heading 360 degrees M and CZA was descending through 3,500 ft, heading 310 degrees M. The controller then asked the crew of CZA to fly a close left base, and advised that they were following a blue and white BAe 146 aircraft (EWM) which was over St Helena Island on left base for runway 19. A short time later, the crew of TNU reported visual. The controller acknowledged this transmission and then instructed EWM to contact the tower.

After making a number of transmissions to other traffic, the controller instructed TNU to turn left heading 310 and to descend to 2,500 ft. He asked the crew if they still had the B737 in sight, adding that it was in their 10 o'clock position at 3 NM. The controller instructed CZA to descend to 1,500 ft. The crew of CZA then reported visual and were cleared by the controller for a visual approach via a close left base. After CZA acknowledged this clearance, the crew of TNU reported that they had the traffic sighted. The controller responded that CZA was for a close left base and cleared TNU for a visual approach. He then instructed CZA to contact the tower and asked the crew of TNU to closely follow CZA. The controller then processed a departing aircraft and accepted the transfer of another inbound aircraft onto his frequency. A turn instruction he gave this aircraft was not initially understood and required two further transmissions for clarification. As this exchange concluded, the controller asked the crew of TNU to confirm that they still had visual contact with the B737. The crew responded that they believed that the B737 had landed. The controller immediately instructed TNU to turn right. He then confirmed with the tower controller that TNU was turning away from CZA. CZA subsequently landed normally on runway 19 and TNU was processed for landing on runway 14.

Recorded radar data indicated that the minimum separation between the aircraft was about 200 ft vertically, and 0.8 NM horizontally. This occurred as TNU was instructed by the approach controller to turn away from CZA. The required separation standard in the circumstances was 1,000 ft vertically or 3 NM horizontally. The data also showed that, at the time CZA was given as traffic to TNU, the groundspeed of CZA was 143 kts while that of TNU was 243 kts. When the crew of TNU reported sighting the traffic, the position of CZA relative to TNU was between 7 and 8 o'clock at about 3 NM rather than 10 o'clock as the controller had indicated a short time earlier. At this time, EWM was at about a 10 o'clock position relative to TNU but at a range of 7 NM.

A review of the automatic voice recording of communications between the approach controller, the aircraft, and other agencies confirmed that there was no request from the control tower for TNU to be processed for runway 14. It also confirmed that the crew of TNU was not given their number in the landing sequence.

Neither TNU, nor CZA, was fitted with a traffic collision avoidance system (TCAS).

The controller

The controller involved was highly experienced. He gained his initial ATC ratings in June 1980. He had been rated and endorsed to perform the radar approach controller duties since April 1990.

The incident occurred two hours after he had commenced duty on the Approach South position. The controller stated that he did not consider the traffic levels and/or workload to be unusually high at the time of the incident. He indicated that he changed the traffic sequence with respect to TNU to reduce his workload and improve traffic management for both himself and the tower.

Information from the crew of VH-TNU

The technical crew of TNU said that, in hindsight, they did not sight CZA at any stage during the sequence. Their report to the controller that they believed the aircraft had landed indicated that they had mis-identified EWM as CZA. The vectors they had been given placed the aircraft high and fast on the descent profile. This, coupled with the checklist actions and the request to sight the traffic, created a high cockpit workload situation. Neither pilot could recall being given their number in the landing sequence.

The cabin flight attendant on TNU became aware of CZA when she saw it through a passenger window as she completed the cabin pre-landing checks. She felt some concern regarding the proximity of the aircraft and considered entering the cockpit to confirm that the pilots knew of its presence. In the event, she decided to take no action, as she felt confident that they would have been aware of the situation.

Brisbane arrival procedures

The management of air traffic in the Brisbane Terminal Area (TMA) involved the formulation of a traffic management plan for arriving and departing aircraft. The Terminal Approach Coordinator (TAC) decided upon the plan after liaison with the Traffic Management Coordinator (TMC) in the control tower. Its purpose was to determine the most efficient use of available runways and types of approaches consistent with prevailing weather conditions and traffic density and patterns. Once the plan was agreed, the TAC directed the Flow Controller to sequence the arriving traffic in accordance with the traffic management plan. The task of the radar approach controller was to direct aircraft in accordance with the plan to ensure that aircraft arrived in sequence at appropriate intervals for efficient traffic flow.

In order to make the best use of the available runways and minimise delays, procedures had been developed to assist controllers with arriving aircraft required to overfly the aerodrome from the south for runway 14. These procedures were detailed in Northern District Local Instructions TMA 27, and were designed to assist in minimising workload on both the approach and control tower controllers by providing a standardised technique which allowed departing aircraft to depart and remain clear of the arriving overflying traffic. The instruction stated:

In the case of RWY 19/01 and an arrival from the east/southeast for landing RWY 14, the following shall apply. The arrival shall be positioned east of the JCW-BN VOR track, tracking direct to the CONTROL TOWER assigned A020 and for the ACFT to be on TWR frequency no later than 5NM with no restrictions.

These tracking requirements will ensure that a RWY 19 LAV SID can proceed unrestricted.

Sight and Follow procedures

At the time of the occurrence, visual separation standards were detailed in the Manual of Air Traffic Services (MATS) Chapter 4, Section 8. Air traffic controllers could use the visual separation standard to separate aircraft flying at or below FL125. However, if this standard was used an instruction to maintain visual separation with, or to follow other aircraft, should have been issued in accordance with requirements of MATS Chapter 6 Section 4. Chapter 8 of MATS, "Enroute/Approach Control", did not make reference to sight and follow procedures.