Loss of separation

Three aircraft were scheduled to depart Melbourne via the 150 radial. VH-KDK and VH-WZI were vectored left of track to allow the faster aircraft, VH-EWL, to safely overtake both of them. A small closing speed existed between VH-KDK and VH-WZI but normal climb performance was such that vertical separation could be expected before radar separation approached minima. The Departures controller in training decided to place VH-KDK back on pilot navigation by instructing the pilot to track direct to Cowes. This resulted in VH-KDK and VH-EWL now being on gradual converging tracks. The trainee thought that VH-EWL would have drawn in front before both aircraft were back on track. In this configuration the aircraft were handed off to the receiving Inner Sector radar controller who was made aware of the converging aircraft and the possible need to alter one of the aircrafts tracks at a later stage. The Inner Sector controller knew that while the separation minima inside 30 miles was three miles, this increased to 5 miles further out. His judgement was that immediate action was not required but that separation needed to be monitored. The Inner Sector controller became distracted when VH-WZI had not made a radio call when transferred from Departures as well as being distracted by other traffic in the Ballarat/Yarrowee area. When he returned his attention to the convergence of VH-KDK and VH-EWL these aircraft were beyond 30 miles from Melbourne but with only three miles lateral separation. A turn was initiated and the required five miles separation was established. Significant Factors The following factors were considered relevant ot the development of the incident: 1. The Inner Sector radar controller was distracted by other aircraft. 2. The Inner Sector radar controllers scanning of the traffic under his control was inadequate. 3. The Inner Sector radar controller did not ensure that the aircraft remained adequately separated.

The B747 VH-OJD departed runway 34 on runway heading and was cleared to 3000 feet. On contact with Sydney Departures VH-OJD was given a left turn heading 240 and was instructed on two occasions to maintain 3000 feet. The aircraft was observed to climb to 3400 feet, and this was confirmed by the pilot. VH-MZX, a PA31 had departed from runway 07 and had been cleared to 4000 feet on a heading of 030. Horizontal and vertical separation standards were infringed as there was only two miles lateral separation by radar between VH-OJD and VH-MZX. The required separation standards was 1000 feet vertically or three miles horizontally.

PK-GIB was tracking from Taroom to Udiko. JA8182 was tracking from Rockhampton to Armidale. Both aircraft were cruising at flight level 370 (F370). The tracks cross at approximately 60 nautical miles (nm) east of Taroom. PK-GIB was instructed to descend to F350 and to be established at that level by 20nm east of Taroom.

Due to language problems between the controller and the Indonesian crew, the controller was later not certain whether the crew had understood the clearance to be level at F350 by 20nm (the lateral separation point) or 30nm east of Taroom. After some further discussion, the controller finally established that the aircraft had not levelled at F350 until 41nm east of Taroom thereby compromising procedural separation standards.

Circumstances

The Canberra air traffic control approach and departures functions were being performed by one controller because of the low traffic density. VH-ILL departed Canberra for the local training areas and intended to transit at 4,000 feet which was the normal altitude for such transit. The approach/departures controller had a flight progress strip and notated this altitude on the strip in the normal manner.

The pilot of VH-ILL then requested a climb to 5,000 feet which was approved as there was no conflicting traffic. The flight progress strip was annotated correctly with this change.

At this time air traffic levels were increasing and it was decided to separate the approach and departures functions. During this transition, control of VH-ILL was taken over by the oncoming departures controller who was given the flight progress strip. The approach controller then replaced this conflict alert tool with another, a red plastic rectangle referred to as a "shrimp boat", which was placed on the radar screen to indicate that there was traffic en route to the training areas. However the controller did not notate an altitude on this shrimp boat.

VH-TAH was arriving at Canberra from Sydney and the approach controller was radar vectoring that aircraft for an approach to runway 35. During this vectoring process the controller descended VH-TAH to 5,000 feet without providing horizontal separation with VH-ILL. The radar screens at Canberra do not show Secondary Surveillance Radar [SSR] Mode C altitude readout, and the controller evidently forgot the height of VH-ILL.

The aircraft came within half a nautical mile and 300 feet of each other. The required separation standard is five nautical miles or 1,000 feet.

Significant Factors

1.The approach controller gave up his main conflict alert reminder when he passed the flight progress strip to the oncoming departures controller.

2.The approach controller did not notate the altitude assigned to VH-ILL on the red shrimp boat.

3. SSR Mode C altitude information is not available at Canberra.

Safety Action

Deficiencies were identified during this investigation and appropriate safety recommendations are being formulated.

The incident occurred just prior to official first light, during a shift change in both the control tower and the departure/arrivals centre and during a busy period.

During multiple departurers in suitable weather conditions, the aerodrome controller is required to retain the aircraft on tower frequency and provide positive visual separation (diverging tracks) until the aircraft are handed off to the departure controller.

VH-FWJ and VH-MLX were departing, in turn, from runway 21 on the Perth to Ballidu track. Departure instructions were given to the aircraft which would allow them an unrestricted climb on headings 30 degrees apart (VH-FWJ on 360 degrees and VH-MLX on 030 degrees). When the departure controller passed the instructions to the aerodrome controller for relay to the aircraft, the aerodrome controller was reminded that he would be responsible for visual separation. However, the controller forgot to instruct the aircraft to remain on the tower frequency.

Both aircraft transferred to departure frequency shortly after take-off. VH-FWJ commenced its turn on to 360 degrees as it passed through 1000 feet, 4 nautical miles from take-off. VH-MLX (with a better climb performance than VH-FWJ) commenced its turn on to 030 degrees as it passed through 1000 feet 2 nautical miles from take-off. The resultant tracks placed the aircraft in potential conflict.

Although the potential conflict was recognised by both the aerodrome controller and the departure controller, corrective instructions had to be passed to the aircraft by the departure controller, resulting in a short delay between when the potential conflict was identified and the aircraft were able to respond. As a result the radar returns came within half a nautical mile horizontally and less than 200 feet vertically. Although the two radar returns appeared to be very close together, the aircraft were observed to be visually apart at all times.

The investigation disclosed that although the traffic load was normal for that time of the day it was significant enough to prevent a comprehensive shift change briefing from being carried out in the tower. Evidence also indicated that the aerodrome controller was distracted by the activity associated with the shift change and this plus the combination of low external light conditions and high workload led to temporary task saturation. Consequently the aerodrome controller did not complete his assigned tasks nor did he register the reminder given by the departure controller.

SIGNIFICANT FACTORS

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

1. The aerodrome controller was distracted from his assigned tasks by the shift change which occurred during a time of high workload and less than optimum light conditions.

2. The aircraft had significantly different climb performance, with the climb profile of VH-FWJ being about half that of VH-MLX.

3. The provision of positive separation instructions from the tower was made difficult because the aircraft were not on the tower frequency. The delay associated with the provision of this information by the departure controller, although not excessive, was sufficient for the conflict to occur.

SAFETY ACTION

The following safety enhancement action was taken after the occurrence.

1. The Civil Aviation Authority reminded relevant Perth staff of the requirements for the application of visual separation during departure.

2. The Civil Aviation Authority took action to rearrange the tower shift change over so that it occurs prior to the known busy period which starts around 0600.

VH-KPY had been cleared to operate on a photographic survey near Perth. VH-HYI was inbound to Perth from the south-east and was tracking via a five nautical mile final for runway 03 when the radar return indicated that the aircraft were approaching the minimum separation standard. The duty Air Traffic Controller recognised the situation and gave avoidance instructions, however they were too late to prevent separation between the aircraft reducing to less than the minimum standard of five nautical miles.

The Air Traffic Controller had poorly planned the arrival of VH-HYI and had allowed himself to become annoyed at a separate co-ordination problem that he had partially created. The annoyance contributed to the reduction in separation standards in as much as it reduced his concentration on the task of maintaining separation between the two aircraft whose closing speed was of the order of 500 knots.

VH-LBA was maintaining FL 270 and northbound from Meekatharra. VH-FKI was southbound to Meekatharra and was cleared to descend from FL 310 to FL 260 through the level assigned to VH-LBA. The duty air traffic controller was advised of this error by the pilot of VH-LBA and VH-FKI was assigned a new clearance which should have provided lateral separation for the descent. However, the controller's calculations were in error and the distance between the aircraft was reduced below the minimum separation standard.

The controller had just completed a hand-over/take-over when he was presented with this slightly more complicated separation problem. Coupled with this was a reduction in currency due to administrative tasks associated with being a team leader. Flight progress strip management practices at Perth may have contributed to the occurrence. Strip procedures have since been modified to be consistent with an apparent national standard developed from discussions with other check control staff.

Circumstances

Canberra approach/departures control was being operated on combine due to training requirements. The training officer had confidence in the trainee's ability to handle the situation as the traffic level was light and the trainee was in his final two weeks of training prior to a rating proficiency check.

VH-WNK [Cessna 210] was maintaining 9,000ft on a flight from King Island to Bankstown and was established on the 210 radial of the Canberra VOR.

VH-EWF [Fokker F28] departed Canberra for Melbourne at 0906 hours and was instructed to maintain 8,000ft due to an expected confliction with VH-WNK.

When the trainee controller identified VH-EWF he expected that the aircraft would climb sufficiently quickly to be able to reach a level above VH-WNK before the radar separation standard of 5nm was infringed. On this basis he climbed VH-EWF to Flight Level 190 with a requirement to report leaving 10,000ft.

As the distance between the two aircraft reduced, the training officer asked the trainee what action he intended to take. The trainee was considering his reply when the training officer instructed him to turn VH-EWF so that radar separation would be maintained. At that precise moment the trainee commenced a transmission to another aircraft on an unrelated matter and a few seconds delay occurred before a radar vector was issued to VH-EWF. The training officer elected not to use the override system as he judged that the time taken to activate the system would be similar to that taken by the trainee to complete the transmission. As the crew of VH-EWF were complying with the instruction the separation reduced to 3nm before the flight paths diverged. As vertical separation had not been established, a breakdown in separation occurred.

Significant Factors

1. The trainee approach/departures controller misjudged the climb performance of VH-EWF.

2. The rated approach/departures controller allowed the situation to develop to the stage where there was insufficient time to guarantee that separation standards would be maintained.

3. The training officer's override facilities were not conducive to immediate correction of a trainee's error.

At 0758 EST, VH-OUD contacted Brisbane Approach 28km north of Brisbane at 3,000 feet requesting an airways clearance. Approach answered that a clearance was not available and that the aircraft was required to remain outside controlled airspace. Approach also told the aircraft to contact the Redcliffe common traffic advisory frequency (CTAF) and to call Approach again at 0805 EST.

Another aircraft, VH-HEI, was on descent inbound to Brisbane and had been assigned 3000 feet. As the progress of this aircraft was being monitored on radar, the Approach Controller realised that VH-OUD had penetrated the control area. Attempts to contact VH-OUD were unsuccessful so VH-HEI was vectored clear of VH-OUD. The separation standard of 5 miles was infringed during this sequence.

The pilot of VH-OUD contacted Approach again about 5 miles north of Brisbane Airport and was processed for landing. The pilot later said that he heard the instruction to remain outside controlled airspace. A short time later, however, he had been told to squawk ident on the aircraft transponder and was informed that VH-OUD had been radar identified. He interpreted this to mean that he could continue into controlled airspace at 3,000 feet.

The pilot of VH-MGW requested taxi clearance for take-off and reported in receipt of automatic terminal information service (ATIS) "Echo". The runway nominated by the ATIS was runway 35. The aircraft was cleared to taxi, but shortly after, the pilot requested runway 30 for departure. The Surface Movement Controller (SMC) then issued the following instruction: - "Mike Golf Whisky taxi for change of runway 30, hold short of runway 35." A Boeing 737 VH-CZD had been cleared to land on runway 35 and was beginning to flare for landing. VH-MGW was then observed to cross the holding point for runway 35. After repeated calls from the SMC the pilot of VH-MGW finally stopped his aircraft close to the edge of the flight strip. The Boeing was not instructed to go-around as it was at the point of touchdown and considered by ATC to be committed to landing.

The pilot of VH-MGW stated he did not see the holding point markings until he had been instructed to stop by the SMC. He said the holding point markings had been changed and was planning to stop at the "old" holding point position. He also stated that he was aware of the landing Boeing 737.