Loss of separation

A group of four aircraft was inbound to Brisbane on the same air route. Three of the aircraft were in close proximity with the lowest cruising at Flight Level(FL) 270 and the other two cruising at FL 350 and FL 370. The fourth aircraft was about 20 miles ahead cruising at FL 330.

The aircraft cruising at FL 370, a Douglas DC-10, requested a clearance to descend when the aircraft was clear of traffic. The air traffic controller immediately cleared the aircraft to descend. The pilot did not respond to the transmission by the controller and the controller again cleared the aircraft to descend. The pilot advised the controller that there was another aircraft three miles ahead at FL 350. The controller apologised to the pilot and issued an instruction to the aircraft, a Boeing 737, cruising at FL 350 to turn right. The pilot of the aircraft at FL 370 then advised that he had the other aircraft in sight and that his aircraft had left FL 370 for FL 350. The controller immediately instructed the aircraft to maintain FL 370.

Examination of the radar recording revealed that the higher aircraft had descended to FL 368 before commencing a climb to FL 370. At that time the aircraft were laterally separated by between four and five miles. As a result there was an infringement of the required separation standard of either 2,000 feet vertical or five miles horizontal separation between the two aircraft.

The controller who issued the descent instruction was a trainee air traffic controller under training for the issue of her initial sector rating. At the time of the occurrence she was being supervised by a rated controller. The rated controller had instructed the trainee to issue the descent instruction to the aircraft and advised that he believed that when doing so the aircraft at FL 350 was in fact at FL 330. He was unaware why he had made that assumption as the altitude of the aircraft was correctly labelled by use of a 'shrimp boat'.

VH-HPL was on track from Perth to Rottnest Island, maintaining 2000 ft when VH-EAJ departed Perth for Singapore. The pilot of VH-EAJ had requested a clearance to enable the aircraft to initially track north along the coast, visually, at 2000 ft. VH-EAJ was cleared initially at 3000 ft. When the aircraft reached 3000 ft the pilot advised that they "would like 2000 if its available .....3000 is just above cloud". VH-EAJ was then cleared to descend to 2500 ft which was the lowest assignable altitude to keep the aircraft 1000 ft above the base of controlled airspace.

At this time VH-EAJ was on radar vectors, heading 280 deg, which was keeping the aircraft to the south of VH-HPL but on a converging track. VH-EAJ was then asked to "report sighting a Britten Norman Islander (VH-HPL) in your two o'clock.....four miles maintaining 2000 ft.......". The crew of VH-EAJ were unable to sight VH-HPL. They were then instructed to climb to their planned cruising level of flight level 350. They were then asked again if they had the traffic sighted but reported "negative we're in cloud". They were then asked their present level and reported they were at 3100 ft.

Separation between the two aircraft reduced to two miles with less than 1000 ft vertical separation.

Circumstances

At 1635 hours VH-TQK departed Port Macquarie for Sydney via a track of 221 deg from Port Macquarie. An airways clearance was issued by RAAF Williamtown Air Traffic Control [ATC] for VH-TQK to enter controlled airspace [CTA] on this track on climb to Flight Level [FL] 160.

At 1537 hours VH-AMS departed Port Macquarie for Williamtown on a track of 200 deg from Port Macquarie. An airways clearance was issued by Williamtown ATC for VH-AMS to enter CTA on this track to FL 140.

The clearances were issued when neither aircraft was identified on radar and with no vertical or longitudinal separation requirement. In such circumstances the only separation standard available is lateral which required 30 deg between the departure tracks in question. As only 21 deg existed, a breakdown in separation occurred.

Radar analysis indicates that the aircraft were 7.6 NM apart when they were established in CTA and that this distance increased before radar identification was complete. It also shows that the vertical difference was a minimum of 500 ft which occurred prior to identification.

Significant Factors

1. The Williamtown air traffic controller issued procedural airways clearances that were not in accordance with the appropriate separation standard.

Singapore Airlines Flight 288 [SIA288] was maintaining Flight Level [FL] 310 on a flight from Auckland to Singapore. It had been cleared to transit Restricted Area R588 at FL 310 by Sydney Sector 5 who had correctly co-ordinated the clearance with Williamtown Approach control.

Four RAAF FA18A aircraft, operating as Shogun Section, had completed an exercise to the south of R588 and requested a clearance from Williamtown Approach control to return to Williamtown for a landing. The controller cleared Shogun Section to transit R588 at FL 310 from south to north on a course that was in conflict with SIA288.

As the aircraft approached each other, Williamtown Approach noticed the confliction and passed traffic information to Shogun Section, who then initiated evasive action by climbing above the level of SIA288.

The crew of SIA288 was not given traffic information by Sydney control but saw two FA18A aircraft and assessed that their own aircraft would pass behind. They therefore elected not to take any other action.

The aircraft passed within 2.7 NM of each other with 900 ft vertical difference. The required separation standard is 5 NM or 2,000 ft and, as such, a breakdown in separation occurred.

Significant Factors

1. The RAAF controller issued clearances for SIA288 and Shogun Section without correct application of the appropriate separation standards.

VH-SMH was on a positioning flight from Camden to Sydney at the conclusion of an instrument rating flight check. The aircraft was instructed to contact Sydney Approach on departure for airways clearance into controlled airspace but was subsequently observed on radar tracking towards Sydney, approximately one mile north of the 062 localiser, climbing through 3000 feet. VH-SMH continued to track parallel to the localiser, reaching 4200 feet by 18 miles from Sydney before contact was established with Sydney Approach. Conflicting traffic was VH-TJN, also inbound to Sydney on the 062 localiser, on descent to 3000 feet. VH-TJN was passing 5000 feet and was about 2 miles ahead of VH-SMH, as it reached 4200 feet.

The pilot of VH-SMH later said that, as with other departures from Camden that day, he had called Camden Ground prior to engine start to advise that he would be taxiing shortly and requested airways clearance. He did not recall what altitude this flight was planned at but said that he would have set 4000 feet on the assigned altitude indicator as this was the lower limit of controlled airspace overhead Camden. Once airborne from runway 26 a simulated engine failure was initiated by the check pilot. Recovery time was minimal, and Camden Tower advised the pilot to call 123.4 (Sydney Approach) for airways clearance. This was accomplished but the pilot said he could not now recall the actual clearance instructions. The controller then asked the pilot if Camden Tower had asked him to call Sydney Approach for a clearance, and did the pilot recall what Camden Tower had said. The pilot advised that Camden Tower had told him to expect clearance at 4000 feet and to call Approach.

Air Traffic Control were expecting VH-SMH to call Sydney Approach and had planned to hold the aircraft for traffic sequencing.

Arrivals radar was being operated by a trainee controller under the supervision of a rated controller. VH-ANJ and VH-FKI were both tracking to Perth via Clackline. The trainee controller had given both heading and altitude instructions to the aircraft in an attempt to manage their separation. A breakdown in separation standards occurred when the aircraft approached to within 3 nautical miles and 500 feet vertically before the instructions took effect. The supervising controller took over and provided VH-FKI with traffic information on VH-ANJ which allowed visual separation to be maintained.

Although the trainee controller recognised that there would be a separation problem the instructions given to the aircraft were not given in time nor were they sufficient to separate the aircraft under all possible conditions.

The supervising controller was slow to take control of the situation because he wished to give the trainee, who was at an advanced stage of training, the opportunity of recognising the situation and making the necessary corrections.

The trainee's task was made more difficult when VH-FKI did not descend as early as anticipated and drifted to the right of the runway 24 localiser, and towards VH-ANJ, after the pilot had reported established.

The following factors led to the development of this occurrence.

1. The trainee controller did not have sufficient expertise to be able to recognise and allow for all possible variables in the traffic conflict situation.

2. The supervising controller made an error of judgement when he delayed his intervention and was unable to prevent the breakdown in separation standards.

3. Whilst not a direct factor, the flight path of VH-FKI complicated the situation.

VH-HYB, on track between Mildura and Griffith, en route to Sydney, was maintaining non-standard Flight Level 380. The non-standard level was approved by air traffic control to help the aircraft avoid turbulence. UTA 147, flying on the same track in the opposite direction was maintaining Flight Level 350 but requested a climb to Flight Level 370. This request was immediately approved by air traffic control Sector 4. An adjacent controller noticed the altitude readout on UTA 147 as Flight Level 363 when both aircraft were about 10 nautical miles apart nose to nose.

He immediately called out to the Sector 4 controller who was engaged in coordination. Before the UTA 147's altitude clearance could be amended to Flight Level 360, to achieve the required 2000 feet vertical separation, the pilot of UTA 147 read back "maintaining Flight Level 370". The controller immediately attempted to pass traffic information to UTA 147 but because of language difficulties, the information was not understood before both aircraft had passed with the reduced separation of 1000 feet.

VH-NID [DHC8] had departed Sydney for Port Macquarie and was maintaining Flight Level [FL]170 and passed Williamtown at 2139 estimating Port Macquarie at 2202 hours [All times are UTC].

VH-RUI [PA31] taxied at Port Macquarie for Williamtown at 2149 hours and was passed traffic on VH-NID by Sydney Flight Service [FS]. At 2150 hours VH-NID called on area frequency and reported leaving FL150 on descent with a circuit estimate for Port Macquarie of 2159 hours. FS passed traffic on VH-RUI to VH-NID informing the crew that VH-RUI was taxiing and would climb to 6000ft.

At 2151 hours VH-RUI gave his departure call on area frequency as time 50 and climbing to 6000ft.

No further calls were made by either crew until 2157.30 hours when VH-NID advised on area frequency that he was changing to MTAF and asked Sydney to confirm the altitude of VH-RUI as 2000ft. VH-RUI advised that he was maintaining 6000ft. Interviews confirm that the incident occurred approximately one minute prior to this transmission.

Both crews agree that the occurrence was approximately 15-20nm south of Port Macquarie and the Automatic Voice Recorder [AVR] analysis, when combined with pilot reports, put the time of passing at between 2156.30 and 2157.00 hours.

The pilot of VH-RUI stated that he first saw VH-NID descending in front of him and about 300ft above, causing him to take violent evasive action.

The crew of VH-NID stated that they saw VH-RUI about 1000m to their left when approaching 7000ft and therefore had no need to limit their descent.

Both crews were given traffic information on each other in a correct and timely manner and stated that they were on track.

The weather was fine with no cloud.

The aircraft was given a requirement to reach FL310 by a specified time (43) in order to gain separation from opposite direction traffic at FL290. After the specified time (at 44) the pilot reported that he was unable to reach FL310 and was unable to maintain FL300. The aircraft was given immediate descent to FL270. Shortly afterwards the pilot advised that he was able to climb to FL310. A procedural breakdown in separation with the opposite direction traffic occurred.

The crew reported that they had maintained the climb rate using the vertical speed of the aircraft autopilot. This had caused the airspeed to decay because the climb performance of the aircraft was unable to sustain the climb rate demanded. It then became necessary for the aircraft to descend in order to regain its speed and performance.

The pilot of VH-LQA was conducting a practice ILS approach for runway 23 at Adelaide Airport. Approaching the localizer (LLZ) at 3000ft air traffic control (ATC) instructed him to enter a holding pattern between 28 and 34 km north-east of Adelaide to maintain horizontal separation standards with VH-YMJ, which had been cleared by ATC to intercept the 23 LLZ at 3000ft, from the east, for its arrival to Adelaide.

After completion of the holding pattern, and not having received any further instructions from ATC, the pilot of VH-LQA believed he could continue the practice ILS without any further clearance and intercepted the LLZ.

He was instructed three times in quick succession to turn right onto a heading of 310 degrees, and the pilot of VH-YMJ was instructed to continue turning left. The two aircraft passed at the same height with less than 5km horizontal separation.