Loss of separation

VH-EBR was tracking from Bali to Sydney via route A576 to Curtin (CIN) and then via route T71 at FL330 (33,000 feet). A40GP was tracking from Melbourne to Singapore via T71 at FL350 and estimating Curtin at 1805 UTC. VH-EBR reported over Curtin at 1742 and requested FL370. The duty controller (on Perth Sector 2, the sector responsible for the section of airspace) checked the distance between VH-EBR and a preceding aircraft tracking on A576 (7 minutes ahead at FL370), because he thought they may be in conflict, and then told VH-EBR to standby while weather diversions were considered. At 1746.49, the controller instructed VH-EBR to climb to FL370.

A40GP was probably slightly to the right of track due to a previous weather diversion, but the aircraft were on opposite tracks with an estimated time of passing of 1753. VH-EBR reported maintaining FL370 at 1753.33 and at 1753.55 asked the controller what separation existed with the traffic that had just passed down their left side. The aircraft would have been at the same level and about 50 miles apart at approximately 3 minutes prior to the time of passing. Vertical separation did not exist until about the time the aircraft passed.

The required standard was vertical separation of 2000 feet 10 minutes prior to the time of passing. The controller did not recognise the confliction between VH-EBR and A40GP. He had been busy in the two hours prior to the incident. 15 aircraft had passed over Curtin and there were many diversions due to weather. However, in the 20 minutes prior to the incident the workload had decreased to a moderate level. The controller indicated that he did not feel fatigued at the time of the incident. He was on his fourth solo shift following three weeks recreation leave.

He had completed three familiarisation shifts immediately after the leave but had not been able to work Sector 2 with any more than light traffic prior to the day of the incident. The initial co-ordination received from Melbourne had A40GP at FL310 but there was a level change to FL350 prior to position T71B. The new level had been correctly carried through to all flight progress strips by the controller. The evidence indicates that the controller had a "mind set" that A40GP was at FL310 and therefore below the level of VH-EBR prior to the change of level to FL370 and would not be a consideration. It is possible that a lack of familiarisation in busy traffic conditions on Sector 2 contributed to the controller's error.

VH-FKI was tracking to Argyle via Fitzroy Crossing at Flight Level (FL) 250 and was approaching its descent point. VH-JJX had departed Kununurra, was on a climb to FL240 and was tracking via route T37. The aircrafts' tracks crossed to the west of Argyle creating the possibility for a traffic conflict. At the time of the potential conflict the duty Air Traffic Controller was working with the aircraft in his own sector (Sector 2) and supervising a trainee controller on another sector (Sector 1).

The rated ATC from Sector 1 was absent on a short-term break. Due to technical restrictions, it was not possible to combine the Sector 1 & 2 consoles during this period (the normal method of covering a short-term break). The controller, realising that the aircraft would probably be in conflict during their respective descent and climb, decided to calculate a minimum lateral separation point between the aircraft and issue VH-FKI with a clearance for its descent which, he believed, would maintain the minimum required separation. To calculate the lateral separation, point the controller had to leave his console and draw a lateral separation diagram on the wall chart display.

During this process he incorrectly used the Curtin to Argyle instead of the Fitzroy Crossing to Argyle track for VH-FKI. Consequently, the minimum lateral separation point calculated by the controller was incorrect and the clearance issued to VH-FKI did not ensure the aircraft would be separated by the required minimum standard (1000 ft vertical separation at least 10 minutes prior to crossing). Fortunately, prior to commencing descent the pilot of VH-FKI checked the position of VH-JJX and delayed his descent until the aircraft had passed.

Safety Action

1. The Civil Aviation Authority (CAA) will publish a lateral separation diagram for the tracks to alleviate the need to draw a diagram on the wall chart.

2. The CAA have taken action which will allow the Sector 1 and Sector 2 consoles to be combined should it be necessary.

Co-ordination was received by Darwin Control from Unjung Pandang for VR-HOZ tracking via air route A461, advising its estimated time at BUTPA and that it was maintaining FL330. The level was read back by the Darwin controller, who then co-ordinated this information to Perth International Flight Service Unit without advising the flight level as this was not required by standard procedures.

The Darwin controller then requested information from Unjung Pandang on V8-RBC, inbound to Darwin on air route B583, which is a converging route with A461. V8-RBC had an estimated time of arrival at the ELBIS position within 10 minutes of the estimated time of arrival for VR-HOZ at the BUTPA position. This required that both aircraft be vertically separated by 2,000 feet when they arrived at these reporting positions. In sequence V8-RBC and VR-HOZ positions for ELBIS and BUTPA were co-ordinated by Perth International Flight Service Unit to Darwin Control, advising that both aircraft were maintaining FL370.

Darwin Control queried the level of VR-HOZ and asked that confirmation be obtained from the aircraft. As a precaution V8-RBC was instructed to descend to FL350. Darwin Control contacted Ujung Pandang who confirmed that VR-HOZ was maintaining FL330, but when contact was made with the aircraft the pilot advised that they had been cleared to FL370 by Manila while in Philippine airspace.

Although the incorrect co-ordination received by Darwin Control resulted in the required vertical separation not being maintained, the aircraft had not come into close proximity of each other when vertical separation was re-established.

Safety Action

The Civil Aviation Authority have issued a local operating instruction at Darwin which requires flight levels to be included in co-ordination between Darwin Control and Perth International Flight Service Unit.

The two aircraft were vectored by Perth Approach and given appropriate clearances to facilitate their relative arrivals at Jandakot from Perth. VH-AUC climbed to a higher altitude than cleared and caused a separation breakdown. The pilot in command of this aircraft was an instructor and had the other aircraft sighted but allowed her concentration to lapse and did not detect that her student had climbed in contravention of their airways clearance.

The B747 was being radar vectored to a long left base to runway 34. The controller became anxious during the aircraft's approach as it was well above a normal descent profile. Despite prompting from the controller, the crew indicated that the descent profile was satisfactory. As the aircraft entered a long final approach, the captain asked for a left orbit to lose altitude as they were too high and not yet in the landing configuration. The B200C was also tracking in from the south-west for left base to runway 34, and about 10 NM behind the B747.

Because of this potential confliction, the controller refused the captain's request and directed the B747 onto a heading of 090 degrees and restricted its descent to 2,000 ft. The B747 crew did not hear or understand the heading restriction, did not read back the radar heading and continued in a right orbit. The controller ordered a reversal of the turn, with which the B747 crew complied. In the meantime, the lateral and vertical separation standards of 3 NM and/or 1,000 ft were compromised between the B200C and the B747.

Both crews were given traffic information on the other aircraft and visual separation was maintained until the radar separation standards were once again established. During the telephone interview, the B747 captain said that the first officer was flying and a little slow in configuring the aircraft. He (the captain) was handling the radio and until entering final approach was still convinced that an approach could be made with track lengthening.

He asked for an orbit to the left being unaware of the position of the following aircraft. He said that they did not hear the heading restriction and assumed that a right orbit was acceptable. The controller made an error of omission in not obtaining a readback of the heading. The controllers workload was light at the time of the incident.

FACTORS

1. The B747 crew of Air France 144 misjudged their descent profile and entered the final approach too high to complete a normal landing.

2. The B747 crew did not follow the instructions issued by ATC.

3. The controller did not obtain a readback of the heading information.

VH-MZX was inbound to Sydney from the north-west and had been given a clearance to descend to 3,000 ft. Thai International 986 (THA 986), which was outbound to the north-west, had just departed runway 34 at Sydney. The aircraft had been instructed to turn left onto a heading of 330 degrees and cleared to climb to 3,000 ft. Subsequently, THA 986 was turned onto a heading of 270 degrees. When the controller responsible for the control of THA 986 realised that both aircraft were at 3,000 ft, he instructed THA 986 to turn right. The closest point of approach of the aircraft was laterally 0.9 NM and vertically 200 ft. The required separation was either 3 NM laterally or 1,000 ft vertically. Control of aircraft in the terminal area at Sydney can be divided among up to four different controllers.

In some cases, it is necessary for aircraft under the control of one controller to temporarily enter the airspace of another controller. In such cases, it is normal practice for the aircraft to remain on one radio frequency under the control of the former controller. To assist with the processing of the aircraft, the controller responsible for each aircraft co-ordinates the passage of aircraft under his control with the controllers responsible for the adjoining airspace. This adds an internal co-ordination workload for any controller involved in this procedure.

On this occasion, VH-MZX was being controlled by the Approach (North) controller and THA 986 by a trainee Departures controller who was being supervised by a rated Departures controller. As THA 986 became airborne, the trainee controller asked the Approach (North) controller if he could vector and climb THA 986 clear of VH-MZX through the Approach (North) airspace. The Approach (North) controller concurred with his request. It was then the responsibility of the trainee Departures controller to separate THA 986 from VH-MZX. The trainee Departures controller believed that the inbound aircraft would only be cleared to descend to 4,000 ft and planned to vector THA 986 below this aircraft at 3,000 ft. This belief stemmed from the fact that this was the technique normally used by his training officer. The realisation that both aircraft were at the same altitude was delayed because the radar screen labels that indicate aircraft altitude had become cluttered because of the number and proximity of aircraft in the area. When the Approach (North) controller observed that the aircraft were in confliction he instructed VH-MZX to turn south.

The aircraft did not respond to the instruction. The pilot of VH-MZX later reported that he had not heard the callsign and the beginning of the instruction and was therefore unaware that the instruction was directed to him. He also advised that he had not seen the other aircraft until it was established in the right turn. This was probably because it was shielded behind a cockpit pillar. The controller supervising the Departures controller also had the expectation that VH-MZX would only descend to 4,000 ft. This expectation was apparently based on his normal technique but neither he nor the trainee had requested the Approach controller to limit the descent of VH-MZX to 4,000 ft. However, the supervisor believed that the trainee was going to vector THA 986 behind VH-MZX and by the time he realised that both aircraft were at about the same level the trainee had taken appropriate action to resolve the conflict and regain separation. The pilot of THA 986 saw the light aircraft as his aircraft was turned to the north and was satisfied that the aircraft were clear of each other.

Significant Factors

1. The airspace structure and air traffic control procedures applying in the Sydney Terminal area resulted in an unnecessary rise in co-ordination workload.

2. The control technique used by the trainee was inappropriate for the traffic disposition in the Sydney terminal area.

3. The Departures Controller did not monitor the techniques and instructions given by his trainee to the extent necessary to ensure adequate separation was maintained.

Safety Action

The division of airspace responsibilities within the approach/departures cell of Sydney AACC is to be changed following trials in the ATS simulator.

These "Structured Airspace" proposals should be implemented during 1994 and are expected to result in procedures whereby the internal co-ordination safety deficiency identified in this report will be alleviated.

Earlier in the day, the C99 had flown from Port Macquarie to Sydney via Kempsey. The aircraft was on the first sector of the return flight. Before taxying the aircraft was issued with a 16 West Maitland Two departure clearance, at 9000 feet. The Captain was the handling pilot. The B767 was inbound to Sydney for a landing on runway 16 and was manoeuvring to remain clear of a line of weather east of the coast. The aircraft was under the control of Sydney Approach and was cleared to descend to 6000 feet. Cloud formations east of the coast between the 030 radial and 090 radial of the Sydney VOR, ranging between 10 and 15 miles, were generating clutter on the Sydney air traffic control radar.

Aircraft departing from runway 16 were requesting clearances to avoid the weather east of the coast. When the C99 pilot reported ready for take-off, an amended departure clearance was issued. The standard instrument departure clearance was cancelled and the aircraft given an initial heading of 100 degrees. After take-off, when contact was established with Sydney Departures, a climb restriction of 5000 feet was issued. This clearance limit was read back correctly and set in the assigned altitude indicator by the handling pilot. The aircraft was not fitted with an altitude alert system. After crossing the coast, the Captain asked the First Officer to request an immediate left turn as cloud build ups were visible about 2 miles ahead of the aircraft.

Sydney Departures cleared the C99 to turn left onto 030 degrees and soon after, for a further left turn onto 010 degrees. After advising the Captain, the First Officer selected a company radio frequency to pass details of their departure and estimated times of arrival. Whilst occupied with this task the First officer neglected to alert the Captain when the aircraft was 1000 feet from the assigned altitude, as required by company procedures. The Captain, who was not adequately monitoring altitude, did not realise this check was missed and climbed the aircraft through 5000 feet. The First Officer queried the altitude when he noticed the aircraft climbing above 6000 feet.

Simultaneously, the Sydney Approach controller noticed a reading of 6400 feet on the radar display of the C99. Due to the proximity of the weather returns, the label for that aircraft was obliterated by the weather return and was seldom readable. The Approach controller immediately advised the Departures controller who in turn asked the aircraft to confirm maintaining 5000 feet. The First officer advised it was not and that the aircraft was on descent to 5000 feet.

Both controllers recognised the separation standards were breached and issued instructions to both aircraft to regain separation. VH-OXE was instructed to continue climb and turn right onto 030 degrees by Sydney Departures. The B767 was instructed to turn left onto 270 degrees and to maintain 6000 feet. VH-OXE was also advised of the relative position of the B767. When the C99 climbed above 5000 feet, the minimum 1000 feet vertical separation standard with the B767 no longer existed. The minimum required lateral separation was 3 miles. The actual lateral separation was reduced to about 1.5 miles.

On radar handoff from Sydney, both aircraft were at Flight Level (FL) 250 and on the Point Lookout-Casino track. The Brisbane Sector 2 controller indicated to Sydney that this arrangement was acceptable. The lead aircraft, VH-NYC had a groundspeed of 290 kt and VH-EWJ 440 kt. The controller was conscious of this and when he gave a 25 degree heading change right to VH-EWJ, he assessed that separation standards would not be infringed. However, it quickly became apparent that this would not be so.

VH-EWJ was then instructed to descend to FL 240. The minimum distance between the aircraft reduced to 3 NM. This occurred when there was 500 ft vertical separation between the aircraft. Workload on Sector 2 at the time was high with both northbound and southbound traffic. There were also some technical problems with the Sector 2 control console and periodic interruptions occurred as technicians rectified the faults. The controller had held a Sector 2 rating for 2 months, having previously been a controller in Darwin for some 18 years.

The factors considered relevant to the development of this occurrence are:

1. The controller was relatively inexperienced in the position.

2. The sector workload was high.

3. There were probable distractions caused by technicians adjusting the console.

4. The controller was late in vectoring the overtaking aircraft.

VH-UCI was operating on a training exercise involving asymmetric flight and had been cleared for a touch-and-go landing on runway 29. The aircraft touched down before the slight rise in the runway and the pilot was unable to see all the runway ahead until reaching the top of the rise. At this time, while travelling at about 95 knots, another aircraft was sighted crossing the runway, in front, from right to left. The take-off was continued and the aircraft cleared each other by about 250 metres. The other aircraft, VH-TFE, had been cleared to taxi but instructed to hold short of runway 29. The pilot acknowledged this instruction but thought he had been cleared to cross the active runway.

VH-ELZ departed Brisbane for Toowoomba and was given an initial heading of 270 degrees. Two minutes later, VH-SGQ departed, also for Toowoomba, and was given a departure heading of 240 degrees. At about the same time, Approach instructed VH-ELZ to turn on to 240 degrees. The aircraft came within 3 miles of one another without vertical separation existing. Approach was occupied by a trainee under the supervision of a training officer at the time of the occurrence.

The trainee had recently transferred from another centre where Tower did not depart aircraft less than three minutes apart. This was to ensure that five miles separation existed when the aircraft contacted Approach. In this instance, the trainee was surprised when VH-SGQ departed less than three minutes after VH-ELZ. The training officer said that he misjudged the level of expertise of the trainee. This probably affected how closely he monitored the trainee, allowing the loss of separation to develop.

The following factors contributed to the development of this occurrence:

1. The Approach position was occupied by a trainee controller under the supervision of a training officer.

2. The trainee expected the second aircraft to be further separated from the first than was the case.

3. The training officer misjudged the level of expertise of the trainee.