Loss of separation

Circumstances:

1.1 VH-TAH

Significant Factors:

1. Incorrect flight data preparation.

2. Probable distraction from primary control function.

3. Information transfer failure relative to airway tracking data.

4. Inappropriate airway route reporting waypoints for transfer of jurisdiction purposes.

Recommendations:

The Civil Aviation Authority should give consideration to

1. reviewing all airway route structures to identify similar airways which do not have a published waypoint at airspace boundaries;

2. allocating waypoint names to all such airways; and

3. in the interim providing airway identification and a readback of that airway during co-ordination exchanges.

Circumstances:

Three aircraft, VH-TBN, VH-HYB and VH-ANF were tracking towards Eildon Weir (ELW) en route to Melbourne from the north-east. VH-TBN was a few miles ahead of the other two aircraft. VH-HYB was cruising at Flight Level 240 (FL 240). The other two aircraft were at higher levels, but VH-TBN was on descent to FL 160. VH-ANF and VH-HYB were required to enter the holding pattern at ELW to facilitate sequencing to Melbourne. VH-TBN was cleared to continue but instructed to reduce speed to 230 kts on descent. VH-TBN was paralleling track about 6 NM to the left to stay clear of the ELW holding pattern traffic. VH-ANF was scheduled to leave ELW before VH HYB and in preparation for this, the sector controller decided to descend VH-ANF below VH-HYB. Because there was only about 2 NM between these two aircraft on track, the sector controller instructed VH-HYB to turn 30` left onto 200`, which was towards the position of VH-TBN. The sector controller passed advice on the track and airspeed details for VH-TBN to the arrivals controller and then transferred control of VH-TBN to that controller. VH-ANF was initially cleared to commence descent to FL 250. Details on the track of VH-HYB and the reason for turning VH-HYB left were also passed to the arrivals controller. Control of VH-HYB was also handed off to the arrivals controller at that time. The crew of VH-HYB were then told to call arrivals control. In response, they acknowledged the instruction and asked the controller to advise the height of the aircraft in front of them. Realising that a loss of separation had developed between VH-HYB and VH-TBN, which had been placed under a speed restriction, the sector controller instructed VH-HYB to turn left onto 030`. He also told the crew that the other aircraft was about 200 ft below. The arrivals control position was being operated by a trainee under the supervision of an instructor. The relative positions of VH-HYB and VH-TBN were checked by the instructor when control of VH-HYB was transferred to them. At the time they were transferred, they were separated by about 5.7 NM. At that time, the minimum allowable separation was 5 NM horizontally or 1,000 ft vertically. The instructor and trainee then became involved in other aspects of the training management task. It was then noticed that the radar returns from VH-TBN and VH-HYB were in close proximity. VH-TBN, which was on descent to FL 160, was instructed to expedite descent. VH-HYB was instructed to make a turn, but the aircraft was still on sector frequency. Separation reduced to a minimum of about 200 ft vertically and one NM horizontally. In giving VH-HYB the initial instruction to turn left onto 200` the sector controller had inadvertently overlooked the potential conflict situation with VH TBN ahead but at a significantly reducing speed. The recorded radar data showed that as the incident developed, the closing speed between the two aircraft increased to about 180 kts. The radar screen labels for each aircraft included a read out of groundspeed. The arrival controllers did not detect the large closing speed. The traffic workload at the time was moderate. The sector controller had a low level of label brightness selected. The high rate of closure between the two aircraft was partly due to the fact that VH-TBN was operating at a reduced airspeed and partly because of the direction of the strong wind, which gave VH-HYB a reduced headwind component while being vectored left of track.

Significant Factors:

The following factors were considered relevant to the development of the incident

1. Significant oversight by the sector controller in vectoring VH-HYB towards VH-TBN, which was ahead and restricted to a slower speed.

2. Strong upper wind situation which increased the ground speed of VH-HYB when it was given a turn onto a heading of 200`.

3. The attention of the two arrivals controllers was diverted at a critical stage and they did not detect the situation of a high closing speed between the two aircraft. This incident is one of eight similar airmiss incidents which are being considered as a part of a special investigation aimed at identifying any ATS systemic deficiencies which may be contributing to airmisses. Any recommendations arising from this and the other reports will be addressed as part of the special investigation.

Circumstances:

Brisbane Sector 4 is the military (RAAF) sector in the Brisbane Area Approach Control Centre. It is normally manned by two RAAF controllers who rotate between the radar and procedural positions. At the time of the occurrence, however, the sector was manned by one RAAF controller. At 0039 hours UTC, VH-CZD reported to Brisbane Sector 5 its position Longreach, Flight Level (FL) 370, estimating Taroom (165 miles from Brisbane) at 0120 hours. This position was coordinated to the Sector 4 controller as Restricted Area R614, which includes the airspace above and to the east of Taroom, was active and under the control of Sector 4. The Sector 4 controller read back the level correctly but annotated FL 270 on the flight progress strip for VH-CZD. At 0109 hours, VH-TJA departed Brisbane tracking via Taroom on climb to FL 350. At 0120 hours, VH-CZD reported to Sector 4 its position Taroom, FL 370, estimating Brisbane at 0049 hours. The Sector 4 controller did not detect that the flight progress strip had been incorrectly annotated. At 0121 hours, and at about 60 m from Brisbane, VH-TJA transferred to Sector 4 frequency and reported maintaining FL 350 estimating Taroom at 0140 hours. On the controller's request, VH-TJA confirmed cruising at FL 350. At 0127 hours, VH-CZD requested descent and was cleared to descend to FL 210. At 0129 hours, VH-CZD reported left FL 370. The crew of VH-CZD recalled seeing VH-TJA pass below and with a lateral separation of a few hundred metres as descent was initiated. The Sector 4 controller reported that the radar returns of the aircraft merged shortly after VH-CZD reported commencing descent. Investigation of the occurrence revealed that the controller's workload during the period leading up to the occurrence was low, with only two aircraft on frequency. The controller also had engaged in extensive non operational communications during this period. It was further established that the controller was facing a number of significant personal issues which could have had a distracting influence and had experienced disturbed sleep on the night before the occurrence. Low workload is a common predisposing factor in many air traffic control occurrences involving individual controllers. Low workload tends to lead to under-arousal or complacency, causing work performance to suffer. Low workload can also provide the opportunity for personal concerns to intrude and divert attention from the primary task. A fatigued person can generally cope with a short burst of mental effort but can have difficulty in conducting protracted monitoring tasks. The controller's failure to detect the discrepancy between the actual flight level of VH-CZD and that annotated on the flight strip was probably due to the controller having a false mental picture of the traffic situation. Fatigue and personal concerns could have reduced the controller's ability to detect information which contradicted the mental picture. The notion that VH-CZD was at FL 270 had begun as a minor slip, but had grown into a strong idea that was resistant to challenge. Even when VH-CZD reported Taroom at FL 370, the controller heard what was expected rather than the actual words spoken.

Significant Factors:

The following factors were considered relevant to the development of the occurrence

1. Personal concerns, non-operational communications and fatigue probably distracted the controller from the primary task.

2. The controller annotated the incorrect altitude on the flight strip for VH-CZD.

3. The controller failed to detect the flight strip error when VH-CZD reported Taroom.

4. VH-CZD was given descent clearance without adequate separation from the conflicting traffic VH-TJA.

History of the flights

A de Havilland DHC-8-315 (Dash 8) was being operated on a scheduled service to Mackay from Townsville under the instrument flight rules (IFR). The crew had been authorised by Brisbane Centre air traffic control to descend their aircraft to 6,000 ft. The duty runway at Mackay was 14 and, at 1503:00 Eastern Standard Time, the crew reported that they were tracking on the 304 degree radial of the Mackay VHF omni-directional radio range (VOR) navigation aid and were 30 NM from Mackay. The Mackay aerodrome controller (ADC) instructed the crew to `Report approaching 6,000 ft with DME [distance measuring equipment] distance’.

An IFR category Boeing 717-200 (717) was being operated on a scheduled service to Mackay from Brisbane. Its crew reported at 1503:22 that they were tracking on the 130 degree radial of the Mackay VOR, also on descent to 6,000 ft. The Brisbane Centre controller had assigned both crews 6,000 ft prior to instructing them to transfer to the Mackay ADC radio frequency. The assignment of the same level was an authorised practice, because the Brisbane Centre controller would continue to radar monitor the separation of all arriving aircraft until the first aircraft was at or below 5,000 ft. The ADC subsequently instructed the 717 crew to descend to 4,000 ft. The crew asked whether they could expect a left base and the ADC responded saying that they could expect a left base to runway 14.

The Dash 8 was in cloud, and at 1506:17 the ADC instructed that crew to descend to 4,700 ft. There was no separation standard being applied between the Dash 8 and the 717 and separation was no longer assured. The infringement of separation was not recognised by the Mackay ADC. The ADC instructed the 717 crew to descend to 3,000 ft and to reduce speed. The crew was told that they were number two to a Dash 8 from the north and the ADC asked them to report when visual. The Dash 8 crew reported approaching 4,700 ft at 14 DME and was instructed to descend to 2,000 ft, not below the DME steps.

At 1507:53, the crew of the 717 reported visual at 7 NM and advised that they were able to track for left base. The ADC told them to maintain 3,000 ft and to track for left downwind. The crew was asked to sight a helicopter in front of them at 2,000 ft and 4 miles east of the aerodrome. The crew replied `for the base runway 14 and looking’.

The crew of the Dash 8 reported visual (clear of cloud) and was cleared to make a visual approach straight in to runway 14 at 1508:38. The crew of the 717 was cleared for a visual approach at 1508:51. The crew of the 717 responded by reading back the clearance. The controller then said `and maintain downwind heading, the Dash 8’s currently at 9 mile’. The 717 crew neither heard, nor responded to, this subsequent transmission. The ADC did not query the lack of acknowledgment of that requirement.

Approximately 90 seconds later, the ADC observed the 717 turning left base and converging with the Dash 8 on final approach. This was a second, and more critical, infringement of separation between the two aircraft.

The crew of the Dash 8, on final approach, observed the 717 turn onto base towards their aircraft. The ADC instructed the crew of the Dash 8 to turn right, away from the 717. The ADC issued traffic information to the 717 crew who, after sighting the Dash 8, elected to maintain 1,500 ft. The ADC confirmed with the Dash 8 crew that they could see the 717 and authorised them to continue the approach. The ADC subsequently instructed the crew of the 717 to climb to 2,000 ft and make a left circuit before returning for landing.

Weather

The weather, reported as Information Golf on the automatic terminal information service, was runway 14, wind 100 degrees M at 16 kts, crosswind 10 kts, visibility greater than 10 kms, cloud scattered at 2,000 ft, showers in the area, temperature 27 degrees C and the barometric pressure at 1012 hectopascals.

The investigation report prepared by Airservices Australia indicated that although the conditions included some haze, conditions were suitable for the application of visual separation.

Airspace

Air traffic controllers from Airport Services Group, Airservices Australia, staffed Mackay Tower, which was a non-radar Class D tower. The Manual of Air Traffic Services (MATS) 9.1.2 stated that Class D airspace encompassed control zones of defined dimensions, and associated control area steps generally below 4,500 ft above mean sea level around designated aerodromes. Some of the lower levels of the Class D airspace at Mackay were below radar coverage. Airspace in the vicinity of Mackay above 4,500 ft was Class C.

In Class C and Class D airspace, an air traffic control service was provided for all IFR aircraft. In Class C airspace, a separation standard was required to be provided between all IFR aircraft, and between IFR aircraft and Visual Flight Rules (VFR) aircraft. In Class D airspace, a separation standard was required to be provided between all IFR aircraft and a separation service was required to be provided between IFR aircraft and Visual Flight Rules (VFR) aircraft airspace.

Equipment For most of the 1990s, controllers sought the provision of a radar display in towers where radar coverage was suitable. This was based on evidence that similar procedures were used in the UK in Class D towers, and in the USA in VFR Towers. Prior to the Sydney Olympics, a Tower Situational Awareness Display (TSAD) was installed in Bankstown Tower and during December 2000 test units were installed in Mackay and Rockhampton towers.

At Mackay, radar data was received by a dedicated personal computer located in the Mackay Maintenance Services division building and, after the data was processed, was relayed for display in the tower cabin. The unit displayed secondary radar returns only. The Mackay TSAD, although operating in the tower, was not approved for operational use because a safety case had not been completed. The Temporary Local Instruction (TLI AS/02/076) stated: `Controllers are reminded that until formal commissioning takes place, TSAD shall not be used in any operational sense (notwithstanding aircraft emergencies).’

Procedural separation

There was no evidence that the incident aircraft were provided with any form of procedural separation. Moreover, there was no evidence to show that the Senior Controller at Mackay or the subsequent investigation conducted by Airservices Australia identified that the ADC had not applied procedural separation standards. This oversight is not unusual, as procedural separation is a highly conceptual, rule-based air traffic control skill that demands cognitive rigour.

All IFR category aircraft in Class D airspace were to be provided with an air traffic control service. MATS defined an air traffic control service as follows: `A service provided for preventing collisions between aircraft, between aircraft and obstructions, and to expedite and maintain an orderly flow of air traffic’.

Radar control is the provision of air traffic control services using radar-derived information. Where radar is not available, procedural control is used. Procedural control is the provision of air traffic control services using information derived from sources other than radar. Such information is usually derived from pilots accurately reporting their aircraft’s position in three dimensions.

MATS stated that in a non-radar environment `controllers shall ensure that position reports are received from all aircraft in Class C and Class D airspace and for IFR flights in Class E airspace, unless: a. otherwise instructed by Air Traffic Control, or b. radar identified, or c. if the flight is specifically exempted’.

The crews of the incident aircraft were never instructed to provide a position report, which would have facilitated the selection and establishment of an appropriate procedural separation standard.

Despite the controller’s oversight in not obtaining aircraft position reports from the crews involved, the controller did provide position information about aircraft to crews. Information such as `traffic for you to sight is a Kawasaki helicopter, he’ll be in your one o’clock low at 2,000, he is 4 miles east of the field at the moment’. Another example was `maintain downwind heading, the Dash 8’s currently at 9 mile’.

Visual separation

Clearances for simultaneous visual approaches were authorised in MATS subject to certain criteria. These criteria were that the flight paths were to be greater than 90 degrees apart and that there was no significant cloud at or below the levels assigned to the aircraft. In addition, actual visibility was to be 30 km or more and both aircraft instructed to report at a distance outside the point at which lateral separation would be infringed and at which distance it was known that visual separation could be applied. The 717 and Dash 8 crews were not instructed to report outside of a lateral separation point.

After the controller had sighted both of the aircraft, the controller was authorised to separate them using visual separation as defined in MATS 4.5. Each crew was required to report when visual as a criterion to be met before they could be assigned a visual approach.

The crew of the Dash 8 was cleared for a straight in visual approach, while the crew of the 717 was tracking to join the circuit on left downwind, maintaining 3000 ft. The 717 crew was trying to sight a helicopter at 2000 ft, when they were also cleared to make a visual approach. The clearance for a visual approach authorised the crew to descend their aircraft below 3,000 ft.

MATS 4.5.2.3 stated: `When aircraft are operating visually as aerodrome traffic or in an Aerodrome Traffic Zone, ATC shall issue clearances designed to maintain separation and/or sequencing instructions, and provide traffic information’.

The controller only partially met the MATS requirement. Although the controller immediately followed up the visual approach clearance and issued a sequencing instruction: `and maintain downwind heading, the Dash 8’s currently at 9 mile’, a readback of the sequencing instruction was neither received nor requested. Traffic information on the Dash 8 was not issued to the crew of the 717.

Clearance readbacks

Air traffic controllers were required by MATS 6.1.13 to ensure that crews read all clearances, or amendment to clearances, back correctly. The accuracy of the readback was to be confirmed by the transmission of the aircraft’s callsign. Key elements of the clearances, instruction or information were to be read back. This included heading instructions.

Organisational aspects

In April 2003, Airservices Australia amended MATS to remove the requirement to pass traffic information to aircraft operating visually in the Aerodrome Traffic Zone (see Visual separation). The change was not reflected in the Manual of Standards Part 172 published by CASA and a safety case was determined to be not required. The amendment was considered by Airservices to be a more flexible requirement for traffic information when a tower controller was visually separating aircraft.

The MATS 4.5.2.3; `When aircraft are operating visually as aerodrome traffic or in an aerodrome traffic zone, ATC shall issue; (a) clearances designed to maintain separation; and/or (b) sequencing instructions; and/or (c) relevant traffic information.'

The previous version of MATS did not have the `and/or' for traffic information, it stated `and’, which indicated a mandatory rather than an optional requirement.

On 5 December 2010, at 1422 Eastern Daylight-saving Time, a breakdown of separation occurred between a Boeing Company B737-7Q8 (737), registered VH-VBF, and a Boeing Company B767-338 (767), registered VH-OGU, on departure from Melbourne Airport, Victoria. The flight crew of the 737 had reduced their aircraft's speed in order to meet a height requirement of the Standard Instrument Departure. The following 767 aircraft climbed at a faster speed.

When the aircraft were transferred from the aerodrome controller to a departures controller, there was 3.4 NM (about 6.3 km) separation between them. The departures controller expected them to climb at a similar speed, and did not recognise the loss of separation assurance. The controller's actions to manage the compromised separation were not fully effective. At one point, radar separation had reduced to 1.9 NM (3.5 km) and vertical separation to 500 ft.

On 12 October 2011, a similar breakdown of separation occurred at Melbourne between an Airbus A320-232 and a Boeing Company 737-8BK. This incident involved different controllers to those involved in the 5 December 2010 incident.

The ATSB identified a safety issue in that the procedures for takeoffs at Melbourne Airport allowed for aircraft to depart relatively close to each other, with no documented requirements to ensure jet aircraft would maintain a set climb speed or to require flight crews to advise air traffic control if that speed could not be achieved. Although the Melbourne procedures were based on those used in Sydney, the Sydney procedures specified a minimum climb speed. The safety assessment report for the Melbourne procedures did not include a detailed comparison of the procedures used in the two locations. In response to the identified safety issue, Airservices Australia has commenced action to establish a standard speed profile for use at radar terminal area aerodromes in Australia, and to ensure that pilots of jet aircraft notify air traffic control when operating at a significantly lower speed than stipulated in that profile.

On 1 December 2010, at 1412 Eastern Daylight-saving Time, a breakdown of separation occurred between a Beech Aircraft Corporation Barron BE58 (BE58), registered VH-VFG, and a SAAB Aircraft Company S340B (S340), registered VH-SBA, near Taree Airport, New South Wales (NSW).

The BE58 was a private flight from Bankstown to Port Macquarie, NSW and the S340 was a scheduled passenger service from Taree to Sydney, NSW. On departure, the S340 was issued a clearance by air traffic control (ATC), with an altitude requirement intended to establish the S340 above the BE58 on a crossing track. When ATC reassessed the proximity of the aircraft and determined that the altitude requirement would not ensure separation, they issued the BE58 with a vectoring instruction.

The separation between the two aircraft reduced to below the required standards. Separation was re-established when the S340 reached 10,000 ft on climb.

This incident highlights the importance for air traffic controllers to continually monitor and reassess their separation plans and implement changes to assure that the required separation standards will be established and maintained. Furthermore, the provision of timely and appropriate traffic information to flight crew, by air traffic control, can significantly enhance pilots' situational awareness.

Airservices Australia (Airservices) has advised that they are conducting a systemic review of a number of Breakdown of Separation occurrences, with outcomes from that review to be considered in terms of further safety improvement. As a short-term safety intervention, Airservices will be conducting an awareness program for Air Traffic Controllers following the publication of this report.

On 5 August 2010, the crew of a Fairchild Industries Inc. SA227-AC aircraft, registered VH-TAG, were cleared for a visual approach to runway 30 at Williamtown aerodrome, New South Wales (NSW) by air traffic control (ATC). The flight was a scheduled passenger service from Canberra, Australian Capital Territory (ACT), with two crew and 18 passengers onboard.

After landing, the crew was instructed by ATC to taxi to holding point Alpha, runway 30. During the taxi, the crew received an amended clearance to taxi to holding point Bravo, runway 30.

On approaching holding point Bravo, the crew checked the runway for other aircraft and taxied beyond the holding point. The crew was instructed by ATC to hold short of runway 30. The crew immediately stopped the aircraft and advised ATC that the aircraft had crossed the holding point, but was about 5 m away from the edge of the runway.

Shortly after, the crew observed a Boeing F/A-18 Hornet aircraft takeoff. About 10 seconds later a second Boeing F/A-18 Hornet took off on runway 30.

The crew discussed the incident and determined that they had not received a clearance to cross runway 30.

This incident highlights the importance of pilots utilising all of their available resources to confirm if the appropriate clearance has been received from ATC. Furthermore, if there is some doubt as to the location of other aircraft operating in the area, contact ATC or the pilot of the other aircraft to establish their position.

On 1 July 2010, at 1003 Eastern Standard Time, a breakdown of separation occurred between an Airbus Industrie A320-232 aircraft and Boeing Company 767-338 aircraft, about 40 NM (74 km) to the north-west of Tamworth, New South Wales. The aircraft were operating on crossing tracks, with an angular displacement between the tracks of about 50°. Both aircraft were operating at standard cruising levels. The enroute air traffic controller first identified the confliction about 2 minutes before the separation breakdown occurred, when both aircraft were maintaining FL360 and there was 26.2 NM (48.5 km) between their lateral positions. An instruction to climb to FL370 was issued to the flight crew of the 767. When there was 14.6 NM (27.04 km) between the aircraft, the controller subsequently instructed the flight crew of the 767 to expedite their aircraft's climb. Shortly before a 1,000 ft separation standard between the 767 and A320 was established, the radar data indicated that longitudinal separation had reduced, below the required standard of 5NM (9.26 km), to 3.8 (7.04 km) NM.

This incident highlighted the importance of the provision of timely and appropriate traffic information to flight crew by air traffic control, in that it can significantly enhance pilots' situational awareness.  It also supported the opportunity for flight crew to enhance the situational awareness of air traffic control, such as in providing direct information regarding individual aircraft performance.

Airservices Australia (Airservices) has advised that they are conducting a systemic review into the number of breakdown of separation occurrences. Outcomes from that review will be considered in terms of further safety improvement. In addition, Airservices has implemented a Compromised Separation Recovery training module for enroute air traffic control groups.

On 4 March 2010, a Boeing Company 717-200 (717) departed Perth, Western Australia (WA) on a scheduled passenger service to Port Hedland, WA.
The aircraft was tracking on a GURAK 3 standard instrument departure, which involved transiting through Pearce military controlled airspace. While maintaining flight level (FL) 1201 and turning left onto a heading of 330 degrees under the control of Pearce air traffic control (ATC), the crew
received a traffic advisory (TA) warning from the traffic alert and collision avoidance system (TCAS). The crew advised ATC and were instructed to continue the turn onto a heading of 360 degrees. During the turn, the crew received a resolution advisory (RA). The crew responded and climbed the aircraft to FL125.

The crew were advised by ATC that the conflicting aircraft, a military-operated Raytheon Aircraft Company 350 (King Air) descending through FL120 on a reciprocal track, had the 717 in sight and was maintaining separation. By this time, the radar separation standard had reduced below the required distance of 3 NM (5.6 km).

This occurrence reinforces the importance of effective coordination between ATC positions, and highlights the challenges faced by air traffic controllers when managing aircraft operating within the same airspace, but under the control of different ATC positions.

On 3 September 2009 at about 1859 Eastern Standard Time, a Boeing 737-838 aircraft was en route from Sydney, New South Wales to Adelaide, South Australia and a Boeing 777-31H aircraft was en route from Melbourne, Victoria to Singapore. The aircraft were on crossing tracks and both were cruising at flight level 300. The air traffic control separation standard was infringed and there was a breakdown of separation.

The air traffic controller responsible for separation of the aircraft had recently completed the air navigation service provider's approved training, but had not recognised the potential conflict between the two aircraft.

As a result of this incident, Airservices Australia has amended the compromised separation recovery component of an air traffic controller's training, and introduced a compromised separation recovery element into its final controller field training.