Loss of separation

FACTUAL INFORMATION

A Boeing 747 (B747) aircraft departed from runway 16 at Melbourne for Bangkok on climb to 3,000 ft. Runway 27 was the nominated departure runway but the aircraft required a departure from runway 16 for operational reasons. Additionally, the crew advised that they could not comply with the requirement to not exceed 250 kts below 10,000 ft. The crew of the B747 tracked the aircraft via a standard instrument departure (SID) that required them to turn right and intercept the outbound track, to the northwest of the aerodrome.

Shortly after the B747 became airborne the aerodrome controller (ADC) requested departure instructions, from the DEP N controller, for a pending Boeing 727 (B727) aircraft departure to Adelaide from runway 27. The B747 was climbing slowly and would cross the intended track of the B727. The ADC suggested to the DEP N controller that the B727 be maintained at 3,000 ft, on departure, after the crew of the B747 had been approved to, and had climbed that aircraft above 4,000 ft. However, the DEP N controller believed that the B727 would climb faster than the B747 and he intended to radar vector that aircraft behind the B727. The DEP N controller approved the departure of the B727 on the planned track. He then approved the crew of the B747 to climb to FL200 and cancelled the speed restriction. He also instructed the crew to cancel the SID and to turn left onto a heading of 270 degrees.

The DEP N controller had been operating at the console for approximately three hours. A busy traffic period had just finished, and traffic numbers were reducing. Traffic levels were moderate when the B727 departed.

After the B727 departed the DEP N controller cancelled the speed restriction below 10,000 ft and approved the crew to track direct to Bordertown on climb to FL200. These measures were meant to assist in increasing the horizontal distance between the two aircraft which were on near parallel westerly tracks with the B747 to the south of the B727.

When both aircraft were approximately 20 NM to the west of Melbourne and at similar levels, the DEP N controller assessed that he could radar vector the B747 behind the B727. He instructed the crew of the B747 to turn right onto a heading of 340 degrees. As the crew was turning the aircraft, the DEP N controller observed that the separation standard of 3 NM was going to be infringed. He instructed the crew of the B747 to turn left onto a heading of 240 degrees. Both crews reported sighting the other aircraft. Separation reduced to 1.5 NM horizontally and 700 ft vertically before radar separation was re-established. There was a breakdown of separation.

ANALYSIS

The DEP N controller did not establish vertical separation between the two aircraft before attempting to radar vector the B747 behind the B727. An instruction to the crew of the B747 to maintain a level 1,000 ft below the level of the B727 would have caused a minor delay to the climb of the B747 but would have ensured that separation was maintained.

SIGNIFICANT FACTORS

1. The DEP N controller did not use appropriate separation assurance techniques.

FACTUAL INFORMATION

A Cessna 550 aircraft had departed Wagga on a training flight to Canberra and was maintaining flight level (FL) 170.

A Saab SF340B aircraft had departed Sydney on a regular public transport flight to Albury and was maintaining FL 120 on the route section between Canberra and Albury. Both aircraft were under radar control.

At 1218 ESuT, the crew of the C550 requested descent and were cleared to FL 130 by air traffic control. The pilot read back FL 120 but this incorrect level was not detected by the controller. One minute later the controller informed the crew of the C550 that there would be a delay for further descent due to crossing traffic (the SF340B) on the Canberra to Albury track.

At 1222, the controller noticed that the radar return for the C550 was indicating FL 120 and was 3 NM from the SF340B on crossing tracks. There was a breakdown of separation.

Radar analysis indicated that at the time vertical separation broke down, the C550 had passed through the intended track of the SF340B by approximately 1 NM and that the closest point between the aircraft was 3 NM. The required separation standard was 5 NM horizontally or 1,000 ft vertically.

ANALYSIS

Air traffic control

Because the controller believed he had heard the crew of the C550 read back FL 130 he annotated this on the flight progress strip. This meant that, in his mind, he had provided separation for the conflict he was expecting to occur. He then monitored the aircraft as they passed in the belief that vertical separation would be maintained until he could re-establish radar separation. It was only when he observed on radar that the C550 was maintaining FL 120 that he realised that a breakdown in separation had occurred. At that time, the aircraft had already passed each other, and separation was increasing.

Flight crew of the C550

The crew thought they heard FL 120 given as the descent instruction and when this read back was not questioned, they continued a normal descent to FL 120, believing it to be the assigned level. They did not see the other aircraft and considered that, as air traffic control were providing separation, any instructions to the other aircraft would not have been queried, even if they indicated a climb through the level of the C550.

SIGNIFICANT FACTORS

1. The crew of the C550 read back an incorrect assigned flight level.

2. The air traffic controller did not detect the incorrect read back.

A Cessna Conquest aircraft (VH-YFD) was enroute Perth to Meekatharra via the Mount Magnet VOR at FL250. Another Conquest (VH-FMQ) was flying in the opposite direction, Meekatharra to Perth via the Mount Magnet VOR at FL240. Both aircraft had filed IFR flight plans, were inside Perth controlled airspace and their Mount Magnet position estimates were within 2 minutes of each other. YFD had advised a DME position for descent to Meekatharra and the Perth Centre controller subsequently calculated that the traffic would be passing and may require separation.

When YFD reached Mount Magnet, the pilot transmitted the position to Perth FIS and reported that he was planning to commence descent 2 minutes later. Perth FIS acknowledged the transmission and passed known traffic. Soon after, Perth Centre, unaware that YFD had changed to FIS frequency, unsuccessfully attempted to establish radio contact with YFD to arrange separation with FMQ. YFD had descended through FMQ's level by the time YFD had returned to the correct frequency.

The Perth Centre controller reviewed the aircraft positions and assessed that a breakdown of separation had probably occurred. Day VMC existed at the time of the incident.

The pilot of YFD reported that whilst he was within regulated duty hours, the day's flying program had changed a number of times with diversions and periods of waiting at various airfields in the heat of the day. He also reported that air traffic and company frequencies were very busy at the time of his transit to Mount Magnet.

FIS staff reported that Perth Centre regularly instructed aircraft to call FIS on descent to Meekatharra for traffic. It was also common for aircraft to call on the FIS frequency without prior notice from Perth Centre due to time constraints and workload.

The planning and attention required to cope with flight diversions and associated effects of waiting in the heat, probably fatigued the pilot and reduced his level of attention. His attention may have also been diverted by the radio traffic during the transit to Mount Magnet. A combination of fatigue, distraction and the regular practice of contacting FIS for descent may have influenced the pilot to contact FIS without direction from Perth Centre.

Due to the regular occurrence of aircraft appearing on frequency without prior notification, the FIS operator did not realise that the aircraft was descending without a clearance.

Perth FIS have reported that they and ATC are reviewing coordination procedures.

ACTUAL INFORMATION

A Boeing 737 (B737) was following a Boeing 767 (B767) for arrival at Brisbane. Both aircraft were from Cairns and were being radar vectored by the Sector 3B controller. The controller was undergoing a periodic check and had seven aircraft on frequency with five being radar vectored for sequencing. The periodic check required the controller's performance at the position to be monitored and assessed by another rated controller (check controller). The aircraft being vectored were in two groups that were approaching Brisbane via different reporting points; SMOKA and PERCH. There was a considerable number of radio transmissions and co-ordination calls relating to the management of the two traffic sequences. The two Boeing aircraft were the last two aircraft in the SMOKA sequence. The controller of an adjacent sector was required, by local instructions, to establish a 20 NM trail between arriving aircraft. This controller asked the Sector 3B controller if this was required. The Sector 3B controller replied that that this was not required. Sector 3B is required to establish a 15 NM trail between aircraft by 40 NM from Brisbane. The following B737 was maintaining a slightly higher groundspeed on descent than the B767 and the distance between the aircraft was reducing. The Sector 3B controller instructed the crew of the B767 to turn onto a heading of 090 degrees, for sequencing, which caused the aircraft to cross the intended track of the B737.

The check controller assessed that the separation would be maintained and continued to monitor the Sector 3B controller's actions. The Sector 3B controller reassessed the situation and instructed the crew of the B737 to maintain FL220. The B767 was on descent to FL170 and the Sector 3B controller instructed the crew to continue descent to FL130. The controller believed that the flight profiles of the aircraft, while complying with his instructions, would achieve vertical separation of 1,000 ft between the two aircraft. This would be attained by the B767 passing through FL210 prior to the horizontal separation reducing to less than 5 NM. A controller on an another position had been observing the situation, with the diminishing horizontal and vertical separation between the two aircraft, and queried the Sector 3B controller as to whether the latter was satisfied with the situation. The Sector 3B controller did not acknowledge this query but immediately instructed the crew of the B737 to turn right a further 10 degrees. He intended to maintain horizontal separation by vectoring the B737 behind the B767. The check controller assessed that the horizontal separation standard would be infringed while there was no vertical separation standard being applied and instructed the Sector 3B controller to issue traffic information to the crew. The provision of traffic information was in accordance with the Manual of Air Traffic Services (MATS). The MATS states that when a separation standard does not exist and in a controller's opinion the proximity of aircraft warrants, traffic information shall be issued to the relevant crews. The crew of the B737 were aware of the B767 and had been watching the aircraft as they approached. The crew of the B737 had reduced speed and as they were discussing that separation appeared to be reducing the Sector 3B controller issued traffic information. The two aircraft passed with horizontal separation of 3.8 NM and vertical separation of 600 ft. There was a breakdown of separation.

ANALYSIS

The Sector 3B controller increased his overall workload by cancelling the requirement for the adjacent sector controller to establish all aircraft in a 20 NM trail. The establishment of a 20 NM trail by the adjacent sector controller would have assisted the Sector 3B controller in managing his workload. His level of work and complexity was compounded by having to achieve the required spacing between aircraft and to manage the two arrival sequences. He did not recognise that the horizontal separation between the B737 and the B767 was reducing. Also, he did not employ appropriate separation assurance techniques before issuing radar vectors to the crew of the B767 that would cause that aircraft to cross in front of the B737 with minimal horizontal separation. The intervention by another controller prompted both the Sector 3B and the check controller to act to maintain separation. However, the turn provided to the crew of the B737 was too late and the check controller was required to instruct the Sector 3B controller to pass traffic information to the crew. The situational awareness of the crew of the B737 assisted in the safe resolution of the incident.

SIGNIFICANT FACTORS

1. The Sector 3B controller cancelled the requirement for the adjacent sector controller to establish aircraft in a 20 NM trail.

2. The Sector 3B controller did not use appropriate separation assurance techniques.

3. The check controller and the Sector 3B controller were slow to react to the reduction in separation between the two aircraft.

FACTUAL INFORMATION

Two BA146s were inbound to Brisbane from the north. Both aircraft were being processed for landing on runway 01. There were thunderstorms in the area north of Brisbane and the crew of the leading BA146 requested approval to divert east and west of the aircraft's cleared track to avoid weather. These diversions were approved by the sector controller, who advised the crew to divert a specific number of miles left or right of track.

A new air route structure had been implemented the previous week and this had introduced significant changes to the handling of traffic. Controllers were consolidating their understanding of the routes and the processing of traffic. The sector controller was suitably rated and traffic numbers were low. Traffic complexity had increased as a result of the route changes and the weather. In previous years, prior to the start of the summer storm activity, the Airservices' Northern District office had issued a temporary local instruction reminding controllers of the impact of aircraft diversions on safety and co-ordination. The local instruction had not been issued for the current season.

The diversions caused the lead BA146 to eventually be displaced approximately 9 NM east of, and parallel to, the second BA146. To maintain separation between the two BA146s, the Flow controller co-ordinated with the sector controller for the eastern BA146 to track via Maleny for an approach to runway 14. The amended track and runway was issued to the crew of that aircraft. The crew advised the controller that further diversions would be required.

The crews of both BA146s were assigned descent and were being separated using radar. The crew of the eastern BA146 transmitted to the sector controller that they were diverting 10 NM right of track due to weather. The sector controller acknowledged the transmission with "Roger". This was approved terminology but the Manual of Air Traffic Services stated that it should not be used in reply to a question requiring a direct answer in the affirmative or negative. The crew of an aircraft requiring diversion from a cleared route, in controlled airspace, are to obtain air traffic control approval prior to changing track. The crew of the BA146 did not request approval for the diversion. The sector controller did not reply to the crew that the change in the aircraft's tracking was approved or disapproved.

The crew of the BA146 assumed the diversion was approved. They tracked the aircraft to the west towards the other BA146. The sector controller became concerned at the diminishing horizontal separation, between the two aircraft, and instructed the western BA146 to turn right onto a heading of 180 degrees due to traffic to the east. The controller instructed the crew of the diverting BA146 to turn right onto a heading of 270 degrees to enable the aircraft to pass behind the other BA146. The controller issued instructions to the crews of both aircraft in an attempt to establish vertical separation of 1,000 ft before horizontal separation reduced to less than the required standard of 5 NM. The sector controller did not issue traffic information to the crews of either aircraft when the horizontal and vertical separation standards were infringed. The Manual of Air Traffic Services states that when a separation standard does not exist, a controller shall issue traffic information to the aircraft concerned when, in his opinion, their proximity warrants it.

Analysis of the radar data showed that the horizontal separation had reduced to 4 NM when the vertical separation was 700 ft. There was a breakdown of separation.

ANALYSIS

Previous approvals by the sector controller for the crew to divert around weather were quite specific. On the last occasion the sector controller acknowledged the transmission but did not provide a positive instruction to the crew. The terminology used by the controller was ambiguous. The crew of the diverting BA146 assumed that the acknowledgement by the sector controller was an approval to divert off track. The crew were distracted by the need to avoid the weather and did not query the controller before diverting off track.

The sector controller did not use suitable separation assurance techniques to ensure that separation was maintained between the aircraft. The use of these techniques was essential for aircraft that were diverting around weather, due to the potential for random tracking and an increase in cockpit workload.

The non-issue of the local instruction may have removed a prompt to the sector controller of the need to apply separation assurance techniques.

The controller was aware that the separation between the two BA146s was reducing and endeavoured to rectify the situation. The provision of traffic information may have enabled one of the crews to sight the other BA146 and to assist in maintaining separation.

SIGNIFICANT FACTORS

1. The Northern district office did not issue the temporary local instruction regarding traffic management aspects during inclement weather.

2. The sector controller did not use appropriate separation assurance techniques.

3. The crew of the BA146 assumed that their intended diversion off track was approved.

4. The sector controller did not issue traffic information to either crew when the vertical and horizontal separation reduced to below the standard.

SAFETY ACTION

Local safety action Airservices Australia Northern District Office management has noted that controllers need to be aware of the impact of diversions and will re-issue the temporary local instruction each October.

FACTUAL INFORMATION

History of the flight

A Boeing 747 (B747) was en route from Sydney to Osaka, tracking via Narrabri, Hamilton Island and Port Moresby. The crew had originally planned at flight level (FL) 310 with the intention of climbing to FL350 prior to entering Papua New Guinea airspace. After departing Sydney, the crew calculated that the aircraft could immediately climb to FL330 and requested a change to that level. This was a non-standard level for the planned track. As the B747 flight was to be conducted under radar control while in Australian airspace, the controller granted approval for the crew to operate at FL330. Subsequently, the change to a non-standard level, for the track being flown, was co-ordinated with all other controllers responsible for the Australian airspace through which the B747 would pass.

A Boeing 737 (B737) had departed from Cairns on a flight to Brisbane and was tracking direct to Mackay at FL330. This aircraft was operating at a standard level for the intended track.

The B747 entered the airspace under the jurisdiction of the Brisbane Sector 7S radar controller as the aircraft passed 75 NM to the west of Rockhampton. To ensure adequate coverage of the sector, the controller was using the 180-NM scale on the radar display. Within the sector, the track of the B747 was to cross five other routes which either converged or intersected. Aircraft using these other routes could operate at standard and non-standard levels relative to the track of the B747.

Sector 7 had two radar positions - Sector 7S and Sector 7V. Additionally, there was a planner position located between these radar positions. The planner controller was assisting the Sector 7V controller and not the Sector 7S controller.

The actual time the B737 entered the Sector 7S area, south of Townsville, was not determined. However, based on groundspeed calculations made by the investigation team, the B737 was estimated to have entered the sector approximately 5 - 10 minutes after the B747. The controller was busy at the time and satisfied with the overall traffic situation but did not appreciate the possibility of the two aircraft coming into conflict. The B747 was at FL330 as it approached Hamilton Island from the south. The tracks for the two aircraft crossed 33 NM south-south-east of Hamilton Island. As the aircraft approached the crossing point, the radar controller was required to coordinate and separate a number of departures from Mackay and Hamilton Island airports.

The horizontal separation between the B747 and the B737 aircraft had reduced to 5.5 NM before the controller observed the proximity of the two aircraft on the radar display. The controller instructed the crew of the B737 to turn right to pass behind the B747.

The crew of the B737 sighted the B747 as the controller issued the avoidance instructions. The crew had previously observed the B747 in the distance, but had not perceived it as an aircraft. They were about to request clarification from the controller about a possible aircraft approaching them, when they were advised to turn right. The B737 crew complied with and acknowledged the instruction. The controller subsequently issued traffic information on the B747 to the crew of the B737.

The crew of the B747 received a Traffic Advisory (TA) warning on the aircraft's Traffic Alert and Collision Avoidance System (TCAS), which indicated traffic at the 10-o'clock position at 4 NM. The crew looked for the traffic but did not sight the B737.

The two aircraft passed with a horizontal separation of approximately 2.4 NM and at the same level. The minimum separation standard required was 5 NM horizontally or 2,000 ft vertically. There was a breakdown of separation.

Aircraft cruising levels

Normally, aircraft are approved to operate at flight levels in accordance with the instrument flight rules (IFR) cruising level table. The table used provided standard vertical separation between aircraft which were flying on easterly (example levels are FL330, FL370 and FL410) and westerly (example levels are FL310, FL350 and FL390) magnetic tracks. Approval to operate at other than standard levels could be granted by an air traffic controller when traffic or other circumstances required a change in level assignment. In order to assign a non-standard level, controllers are required to consider the implications on workload and coordination, and the effect on other aircraft which were operating at standard levels. These aspects were considered prior to the B747 crew receiving approval to operate at a non-standard level.

Sector 7S

The Sector 7S controller was responsible for the provision of en-route control services for transiting aircraft as well as arrival and departure control services for aircraft inbound/outbound from airports within the sector which covers a large portion of the Queensland central coast. Additionally, the controller was responsible for the provision of a radar advisory service (RAS) and a search-and-rescue (SAR) alerting service for aircraft operating in non-controlled airspace within radar coverage in the eastern portion of the sector.

Controllers were aware of the potential problems with the crossing routes on this sector, and similar situations were practised in the simulator and encountered on a regular basis when operating the position.

Sector 7S controller

The controller had two and a half years experience in air traffic control and had recently passed a proficiency assessment. He had worked the same shift period the previous day and was adequately rested.

He had been on duty in the position for approximately 50 minutes prior to the occurrence, during which there had been a steady increase in traffic. He appreciated the level and complexity of the traffic situation at the time and felt comfortable with his control performance. He had not considered requesting assistance from the planner controller.

Sector 7 planner

The Sector 7 roster had recently been amended to facilitate staffing of the planner position during nominated times. These times covered anticipated busy periods when the planner controller would be of assistance to the two radar positions. The planner controller conducted coordination with other air traffic service (ATS) agencies on behalf of both radar controllers. This enabled the radar controllers to concentrate on the separation and management of traffic within their respective areas of responsibility.

When all three positions were staffed, the planner and radar controllers shared a communication line to a number of approach control centres serving airports within the two radar sectors. When this line was being used by any of the Sector 7 positions for coordination, it could not be used by either of the other two positions. Consequently, coordination to and from other ATS agencies was often delayed until the line became available. Also, the planner position had facilities to enable a controller to monitor the air-ground-air program of the two radar positions. The planner controller could monitor both radar positions concurrently.

Subject to workload, the planner controller could observe the performance of the radar controllers and provide some assistance to separate traffic if required. The planner controller was required to manage the assistance provided to any one radar controller to ensure it was not to the detriment of the other radar controller.

Traffic situation

The tracks and levels of the departing aircraft from the Mackay and Hamilton Island airports required, the Sector 7S controller to employ step-climb procedures. Subsequently, he spent some time ensuring separation between a number of aircraft in the area to the immediate south of Mackay. At the same time, he was monitoring another radio frequency expecting a transmission from the pilot of an aircraft which was due to arrive at Shute Harbour. The controller also had a number of other aircraft throughout the sector operating on both the control and RAS frequencies.

ANALYSIS

Flight routes and cruising levels

Generally, the operation of aircraft at levels in accordance with the IFR cruising level table would have provided the standard vertical separation of 2,000 ft between the two aircraft. However, because the route of the B747 intersected a number of north and southbound air routes, it would have conflicted with one of the routes, no matter what level was maintained. Action to separate aircraft on the various crossing routes was required on a regular basis. This required one aircraft to operate at a non-standard level or to be radar vectored until the situation was resolved.

As the B747 was to cross a number of routes which may have other aircraft at the same level, the safety net provided by the use of the cruising table levels was not available.

Sector 7 radar controller

The B747 and the B737 entered the sector at its southern and northern extremities respectively. The distance between these entry points (approximately 160 NM on the radar display), possibly made it difficult for the controller to appreciate the future potential for conflict between the aircraft. Also, the controller was dealing with a number of aircraft in the area south of Mackay and was distracted from regularly scanning the full display. These aspects combined to create a situation where the controller did not develop an awareness of the potential conflict.

The provision of assistance from the planner controller may have reduced some of the workload and enabled the radar controller to widen his scan of the sector. This may have enabled him to recognise the pending conflict between the B747 and the B737. Alternatively, the planner controller may have recognised the potential conflict and alerted the radar controller prior to the horizontal separation reducing to the minimum. However, because the planner controller was assisting the Sector 7V controller, she was unable to assist the Sector 7S controller or monitor his display. The radar controller thought he was coping adequately with the situation, and consequently did not request any assistance.

After resolving the situation near Mackay, the radar controller turned his attention to other areas of the sector. He quickly realised the situation and provided instructions to the crew of the B737 to avoid the B747. Generally, when there is a breakdown in separation, the provision of traffic information to the crews of the aircraft involved has priority. However, in this incident the priority was to have the B737 crew turn their aircraft away from the B747. Under the circumstances, the radar controller's momentary pause to receive an acknowledgment from the crew of the B737 prior to issuing traffic information was judicious. By this action, he was able to assure himself that the B737 crew had received the essential avoidance instructions before transmitting the traffic information.

The large scale and the variety of aviation activities occurring within the Sector 7S area made management of the sector difficult at times. The sector controller was required to resolve a number of conflicts within the sector concurrently. This resulted in the controller's attention being focused on one particular area of the display while separation action was being implemented. Consequently, other areas of the display did not receive adequate monitoring.

Human factors considerations

The controller was required to provide en-route control services to high-level transiting aircraft, an arrival/departure control service to aircraft operating to and from the underlying airports, and a RAS and SAR alerting service. The first two services are similar in implementation but generally cover different height bands. However, the provision of a RAS and a SAR alerting service represents significantly different types of tasks in cognitive terms compared to the other services. A study of United States Federal Aviation Authority air route traffic control centres (Bruce and colleagues,1993) indicated that a controller's task load is not solely related to increasing traffic, but is also very much conditional upon the degree of change in complexity of the overall traffic situation. Such was the case in the leadup to this incident.

A controller needs to be able to recognise the change in task complexity as well as an increase in traffic activity to manage the overall task better. Training for controllers to develop a specific awareness of when they are approaching task saturation would be a defence for future incidents. Also, resources should be readily available to provide assistance when controllers recognise that they are approaching task saturation.

For most of the time the controller may have been capable of readily providing all the required services concurrently. However, the differences in the types of the services provided and the spread of the traffic in the vertical and lateral planes across the sector, resulted in the controller requiring a complex management plan to be able to adequately manage the task. Consequently, because of this complexity, the total task load increased to the point where the controller may have become task-saturated.

Sector 7 planner

During busy periods, the planner controller could only provide limited assistance to the two radar controllers. This was mainly due to the limitations of the single available communications line to some of the other ATS agencies. The mode of operation of the communication line reduced the flexibility for the planner and the radar controllers to conduct timely coordination. Often when the line was available, the controllers were busy communicating with aircraft or conducting coordination with other Brisbane ATS positions. Provision of separate communication lines to the two radar and the planner positions would enable all three to conduct coordination concurrently. This would provide more options to reduce the task load.

The planner controller was the only immediate "safety valve" available to either radar controller should the latter approach an overload situation. Modification of the planner position to enable another controller to assist at the position may be warranted. This would ensure that assistance was readily available to either radar position which in turn would limit the possibility of future controller task saturation.

SIGNIFICANT FACTORS

1. The planned route of the B747 crossed a number of other routes which could have other traffic at the same level.

2. The controller was responsible for the provision of different services within a sector in which a number of areas required close monitoring concurrently.

3. The controller's attention was focused on separating traffic located immediately to the south of Mackay to the detriment of maintaining a regular scan throughout the total area of his responsibility.

4. The controller believed he was coping with the situation and did not consider requesting assistance from the planner controller.

5. The planner controller was assisting the Sector 7V controller and was unable to assist the Sector 7S controller.

SAFETY ACTION

This investigation identified specific safety deficiencies associated with the provision of ATC services in Brisbane Sector 7. The deficiencies were related to the complexity and workload of the Sector 7 radar controller, to the provision of only one planner controller to assist the two radar controllers and the limited communication facilities for the planner to assist the radar controllers.

The complexity and workload issues were compounded by the Sector 7 radar controller being responsible for a RAS as well as an en-route ATC service. This issue has been addressed by IR960009 which was issued on the 14 August 1997. The Interim Recommendation stated:

"The Bureau of Air Safety Investigation recommends that Airservices Australia re-assess the safety implications of providing a radar advisory service in conjunction with a radar control service."

On 15 September 1997, Airservices Australia responded to the draft occurrence report and advised that they had reviewed the implications of providing a radar advisory service in conjunction with a radar control service and were satisfied with the service currently provided in this sector.

Airservices Australia also advised that team leaders were rostered from 0600 to 2000 hours daily who were able to monitor the workload and complexity of each position and were able to take appropriate action to maintain the integrity of the positions.

The provision of additional facilities was addressed by Safety Advisory Notice (SAN) 970130 which was issued on the 17 September 1997 to Airservices Australia and the Royal Australian Air Force. The SAN was related to this and a number of other occurrences and identified the following safety deficiency:

"Aircraft movement coordination between Brisbane Sector 7 and Townsville ATC operator positions is constrained at times by the single inter-communication line."

Airservices Australia have informally advised that they intend to modify the two Sector 7 radar consoles to provide independent satellite communication facilities in late 1997 in conjunction with other scheduled engineering modifications.

The overall aspects of the ATC task methodology and human performance will be examined in a detailed study by the Bureau of Air Safety Investigation.

The pilot of the Piper PA31 had submitted details for an IFR flight from Lord Howe Island to Sydney via MAGOO and CHEZA at 9,000 ft, estimating CHEZA (60 NM from Sydney on the 084 radial), at 1835. At 1825 the pilot called Brisbane Centre for a clearance and was instructed to squawk transponder code 2350. The aircraft was identified at 50 NM from Sydney, on the 059 radial. This placed the aircraft some 22 NM right of track, within controlled airspace, and in potential conflict with an outbound Boeing 747.

The pilot of the PA31 later reported that he had been initially tracking on a bearing from the Lord Howe Island NDB. However, at the time of the incident he was unable to receive any Sydney radio navigation aids, and was navigating on time intervals and dead reckoning. The PA31 was squawking transponder code 2000 prior to calling Brisbane Centre. The crew of the B747 did not receive any Traffic Alert and Collision Avoidance System (TCAS) warning. Brisbane radar did not record any transponder returns from the PA31 prior to the aircraft squawking code 2350.

FACTUAL INFORMATION

History of the flight

An Airbus A320 was inbound to Melbourne aerodrome and the crew had been cleared to track via an ARBEY four standard arrival route (STAR) on descent to 4,000 ft. The A320 was the third aircraft to track via the ARBEY four STAR in the arrival sequence for runway 27, under the control of the approach controller.

The ARBEY four STAR was being used to facilitate the arrival of aircraft primarily from the west and north of Melbourne to runway 27. Flight crews cleared via the STAR were required to initially track in a southerly direction to the Fentons Hill very high frequency omni-directional radio range (VOR) navigation aid and then turn left to track 106 degrees to a position on right base for runway 27 at 9 NM from the aerodrome. From this position, aircraft were to turn right to intercept final for runway 27.

For sequencing with other aircraft, the approach controller had cancelled the tracking via the ARBEY four STAR for two previous aircraft, and he intended to do the same for the A320. He planned to issue a heading to the crew of the A320 which would continue the aircraft in an easterly direction. The approach controller had limited the descent of the A320 to 4,000 ft to ensure that the aircraft remained in controlled airspace when it was on the easterly heading. His intention was to maintain the A320 north of the extended centreline of runway 27, for separation and sequencing, and to eventually radar vector the aircraft onto final.

The approach controller did not instruct the crew of the A320 to cancel the STAR or to adopt an easterly radar heading, and the crew continued tracking via the STAR. The approach controller was under the impression that the crew was maintaining an easterly radar heading. The A320 was heading 106 degrees in accordance with the STAR procedure and was slowly converging on the extended centreline of runway 27 from the north.

As the A320 approached the point at which the aircraft would be turned onto final, the crew reported to the approach controller that they were maintaining 4,000 ft. The approach controller acknowledged the report.

A Saab SF-340, inbound from the southeast, was being radar vectored by the approach controller via a left base for runway 27. The approach controller was using radar to separate a number of aircraft inbound from the east and an aircraft north of Moorabbin (located southeast of Melbourne aerodrome) inbound to that aerodrome. The approach controller vectored the SF-340 through the runway 27 centreline for sequencing with the aircraft ahead on final and instructed the crew to descend to 2,000 ft.

The approach controller meant to instruct the crew of the SF-340 to turn left to intercept final for runway 27, but he actually said turn right. As he corrected the direction of the turn to the crew of the SF-340, he observed that the A320 was turning right onto final and was going to conflict with the SF-340. The approach controller instructed the crew of the A320 to cancel the STAR and to turn left heading 120 degrees. He advised the crew of the A320 of the location of the SF-340 and asked them to report sighting that aircraft. The crew of the A320 reported that they had the SF-340 in sight. The horizontal separation between the two aircraft was 1.5 NM and the SF-340 had descended through the level of the A320. The required separation was 3 NM horizontally or 1,000 ft vertically. There was a breakdown of separation.

The approach controller

The approach controller was a team leader and was undergoing a performance check on the position. The controller operated the position, unobserved by the check controller, for approximatetly 45 minutes while the latter completed some administration. The approach controller was not using flight progress strips for arriving aircraft, although he did have access to the flow controller's strips which indicated the arrival sequence. The use of flight progress strips was not mandatory at the position. During the period at the position the number of aircraft under his control had gradually increased. Analysis of the flow controller's flight progress strips and the radar recording indicated a busy and moderately complex traffic sequence during this period. The check controller returned to the position just prior to the occurrence.

The performance of team leaders was checked in the same manner as other controllers with the exception that the performance and check report was not scored. The check controller was only required to assess the team leader's performance as a pass or fail, and to comment on any shortcomings. The comments provide a history of team leaders' strengths and weaknesses. Other controllers received a score in addition to the comments on their performance and check reports. This provided a history of their performance in addition to the comments on any other aspects of their control. The approach controller maintained his air traffic control skills through regularly exercising his seven ratings. As a team leader this had proven to be difficult to manage at times due to his other administrative and management commitments. Training of other controllers for ratings and consolidation of rated controllers in the various positions reduced the opportunities for him to practice his skills as much as he would have wanted. The approach controller felt that in recent years he had slowed down in his performance of control tasks because of the reduced time at the various radar positions.

ANALYSIS

The approach controller felt that his proficiency at the position had reduced to a level less than he preferred as a result of the limited opportunities to practise his skills. This was mainly due to the team leader duties requiring the majority of his time and an inability to obtain access to radar positions because of the training/consolidation commitments for other controllers. It is possible that a higher level of proficiency would have enabled him to better manage the workload. The degree to which this aspect contributed to the incident could not be ascertained.

Distraction as a result of the problems with traffic in the Moorabbin area and the minor difference between the STAR track and the intended radar heading, probably caused the approach controller to not detect that the A320 was still tracking via the STAR. Once he had accepted this situation, there was nothing to alert or remind him that this was not the case, until the A320 turned right onto final approach for runway 27. The lack of any means to readily display the intended track of an aircraft would appear to indicate that controllers must use their working memory to retain such details. However, the limited capacity of working memory and its limited tolerance to interruptions means that information is often forgotten. Facilities, equipment or procedures that may assist controllers to remember essential details would be beneficial. 

The workload due to the level and complexity of the traffic sequence allowed little time for the approach controller to review his actions. The cancellation of the STAR for the two previous aircraft may have led him to believe that he had also cancelled the STAR for the A320.

The "Maintaining 4,000 ft" report by the crew of the A320 probably alerted the approach controller to the location of the A320. However, he was unaware of the potential conflict until the A320 turned onto final.

SIGNIFICANT FACTORS

1. The approach controller's proficiency was not at an optimum level.

2. The approach controller was unable to adequately review his actions because of the workload associated with the busy traffic sequence.

3. The approach controller did not cancel the STAR with the crew of the A320.

4. There was no segregation between aircraft on the STAR and aircraft on final for RWY 27.

5. The approach controller did not notice that the A320 was continuing to track via the STAR until the aircraft turned base.

SAFETY ACTION

Local safety action

Airservices Australia has amended the STAR to provide horizontal separation between the downwind portion of the procedure and the extended centreline of runway 27.

Bureau of Air Safety Investigation safety action 

The Bureau of Air Safety Investigation is reviewing issues associated with team leaders' maintenance of proficiency and their performance assessment. Any recommendations arising from this investigation will be published in the Quarterly Safety Deficiency Report.

Three aircraft were being processed by Brisbane Sector 3B for arrival at Maroochydore. VH-CZB was tracking via position TRIKI (21 NM, 128 degrees from Maroochydore) and was on descent to 6,000 ft. VH-PIE was level at 5,000 ft and also tracking via TRIKI. Another aircraft was on the Brisbane-Maroochydore direct track at 4,500 ft. Seven other aircraft were under the control of Sector 3B at the time. Because of the workload in the sector, PIE had been maintained on Brisbane Approach frequency, although the Sector 3B controller had a flight strip for the aircraft at his control position.

When CZB reported approaching 6,000 ft, it was cleared for further descent to 5,500 ft. This provided vertical separation with the aircraft on the Brisbane- Maroochydore track but not with PIE. About 20 seconds after clearing CZB to 5,500 ft, the controller realised that it would conflict with PIE. He instructed CZB to maintain 6,000 ft but the aircraft was already at 5,500 ft. At the time, CZB was 3.4 NM ahead of PIE. The separation standard required was 5 NM or 1,000 ft.

At the time of the incident, there were 10 aircraft on the control frequency. In this high workload situation, the controller had initially forgotten about PIE. Because PIE was on another radio frequency, the option of descending that aircraft to a lower level when he became aware of the confliction was not available.

FACTUAL INFORMATION

Two aircraft were taxiing at Darwin for departure from runway 11. The crew of VH-EFB, a C210, had received an airways clearance to track via the 184 radial of the Darwin Very High Frequency Omni-directional Beacon (VOR) on climb to 8,500 ft. The crew of VH-HYK, an A320, were cleared via the 163 radial of the Darwin VOR.

The weather was quoted as being 2 oktas at 2,500 ft with visibility in excess of 10 km. Tower controllers considered that the cloud had built up to 3 - 4 oktas at the time of the occurrence and most of that was in the southern sector, where the aircraft were due to transit.

The tower controller obtained departure clearances from the approach radar controller that would allow him to visually separate the aircraft in their respective right turns from the runway heading to their cleared tracks. Radar separation was not expected to occur during this initial stage of flight.

EFB departed and the crew turned the aircraft in accordance with their instructions to intercept the 184 VOR radial, and changed frequency to contact approach radar. The crew of the A320 then became airborne and were instructed to change frequency to approach radar, which they did. As the A320 approached the 163 VOR radial, it disappeared from the view of the tower controller behind, or into, cloud. At this point visual separation could no longer be provided and the approach radar controller could not guarantee radar separation until both aircraft were established on their departure tracks.

The A320 passed marginally through its assigned track before the crew made a corrective adjustment. This track correction occurred at the same time that the tower controller lost sight of the A320 and at a position approximately 5NM south-east of the aerodrome.

The approach radar controller, realising that he could not expect to obtain radar separation for a further minute or two, maintained EFB at 3,000 ft and co-ordinated with the tower controller to confirm that he was still providing visual separation. When the reply was negative, the radar controller was unable to apply corrective action before a breakdown in separation occurred. The aircraft came within 2 NM horizontally and 600 ft vertically of each other. The appropriate standard is either 3 NM by radar or 1,000 ft vertically.

ANALYSIS

The tower controller was inexperienced in the position having only six months service since obtaining his tower rating. The tower and radar controllers had agreed to a course of action that required the tower controller to provide visual separation until a radar standard could be achieved. Because of the relatively close proximity of the departure tracks, this was not expected to occur until the aircraft were approximately 8 - 10 NM from the aerodrome. As the cloud cover was predominantly in this sector, some doubt should have existed as to the ability of the tower controller to guarantee continuous visual contact with both aircraft until a radar separation standard existed.

The fact that the A320 went marginally through the assigned radial did exacerbate the situation. However, this type of minor adjustment is common with the larger aircraft when given turns of this nature and should be considered in any decision regarding separation.

The tower controller was unsure of his responsibilities with regard to providing visual separation and found that the guidance given in the Australian Manual of Air Traffic Services was insufficient. After asking the opinion of several other tower controllers, the investigation team found a general lack of understanding of the application of visual separation principles.

SIGNIFICANT FACTORS

1. The tower controller did not provide visual separation for the entire period prior to radar separation being achieved.

2. The tower controller was unsure of his full responsibilities in regard to providing visual separation.

SAFETY ACTION

The Bureau of Air Safety Investigation is evaluating aspects of visual separation responsibility and how the subject is addressed in the Manual of Air Traffic Services. Any forthcoming recommendations will be published in the Quarterly Safety Deficiency report.