Circumstances:

Before the flight and in the presence of the only passenger, the pilot of the Chieftain asked the pilot of the Cessna whether he had been "dumped" yet. The Cessna pilot did not know what was meant by the term and his colleague would not elaborate. The Cessna departed, followed by the Chieftain about one minute later. The flight planned heights for each aircraft for entry into the Mackay Control Zone were 3000 feet (Cessna) and 2500 feet (Chieftain). The pilot of the Chieftain reported that he climbed to 3000 feet outside controlled airspace, maintaining visual contact with the other aircraft and pointing it out to the passenger, who occupied the front right seat of the aircraft. The Chieftain was closing with the Cessna at a rate of about 20 knots when the pilot lost sight of the other aircraft. Impact occurred when the Chieftain struck the Cessna from above, the right wing tip of the Chieftain striking the right aileron of the Cessna. At about the same time, the right tailplane of the Chieftain struck the fin and rudder of the Cessna. As the Chieftain continued its passage over the other aircraft its tail cone contacted the outboard leading edge of the right wing of the Cessna. Both aircraft remained flyable and landed at the nearest aerodrome. Neither pilot declared an emergency. Later, the pilot of the Chieftain said that he meant to overfly the Cessna and descend ahead of it to give the other pilot "a big scare" as part of his initiation into bush flying.

Significant Factors:

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

1. The pilot of the Chieftain conducted an unnecessary hazardous operation.

2. The pilot of the Chieftain misjudged the closing speed, distance, and relative height between the two aircraft.

When the pilot of VH-MXL lodged his flight plan, relevant details were inadvertently not transmitted to all necessary recipients by the AFTN system. As a result, Melbourne Approach was unaware of the planned track of the aircraft. The flight evidently proceeded normally until the pilot had reported his position at Port Phillip Heads to Melbourne Flight Service, and had requested an airways clearance. Essendon aerodrome was closed to Visual Flight Rules operations, and Melbourne Approach, after receiving details from Flight Service, cleared the aircraft to enter controlled airspace at 4000 feet on track from Port Phillip Heads to Essendon. This clearance was passed to the aircraft 11 minutes after the initial request. The Approach controller had not been informed that the aircraft was tracking via Frankston, a track which crossed the NDB instrument letdown pattern for Moorabbin. Shortly afterwards the aircraft was identified on radar by the Approach controller, and it became evident that the aircraft was in conflict with VH-TKM, which was conducting an instrument approach to Moorabbin. The airways clearance for VH-MXL was cancelled, but before positive action could be taken the aircraft passed within about half a kilometre of each other. It was considered that a number of communication breakdowns contributed to this incident. (a) The flight plan was incorrectly addressed. (b) The relevant Flight Service officer did not inform Melbourne Approach of the tracking details of the aircraft. (c) The Flight Service officer did not query the clearance as issued, although he was aware of the tracking details. (d) The pilot did not query the clearance, although it would have been virtually impossible for him to comply with the tracking instructions from his present position.

Circumstances:

The pilot of VH-BFT, who had limited experience in General Aviation Airport Procedures (GAAP), had completed a successful period, of dual instruction, immediately prior to the accident flight and was on a solo circuit when the accident occurred. The pilot of VH-TNO was completing the first circuit following a solo period in the training area. As VH-TNO rejoined the circuit via the crosswind leg, a route which placed VH-TNO in front of VH-BFT on downwind, VH-BFT was turning downwind from its first take off. The pilot of VH-BFT gave a downwind call, in the early downwind position, and was told by the Aerodrome Controller to follow the Cessna entering mid downwind in the 10 o'clock position (VH-TNO). VH-BFT's pilot acknowledged the instruction. The pilot of VH TNO then gave a mid to late downwind call and was told to follow the twin (VH-DEP a Piper Navajo) on late downwind. The sequence VH-DEP, on late downwind, VH-TNO, mid to late downwind, and VH-BFT, early to mid downwind was then established. The pilot of VH-BFT did not sight VH-TNO at any stage, on downwind, and instead identified the twin on late downwind as the aircraft to follow. The pilot of VH-TNO sighted and followed the twin, as instructed. VH-TNO's pilot also sighted VH-BFT behind and to the right and assessed that VH-BFT was clear of VH-TNO. The two aircraft proceeded to carry out normal circuits. During their independent turns onto final approach, for runway 06, VH-BFT, which turned base leg inside VH-TNO, descended onto VH-TNO from above, behind, and slightly to VH-TNO's left. VH-BFT's right wing tip leading edge contacted the top of VH-TNO's vertical stabilizer bending the top one third of the rudder, causing it to jam, and denting and dislodging the fairing at the top of the tail fin. The relative positions of the two aircraft during the base leg and turn onto final approach prevented either pilot from seeing the other aircraft until after the collision. Following the collision the pilot of VH TNO realised that something had happened, that the aircraft rudder was jammed and that an immediate landing was necessary. The pilot of VH-TNO continued straight ahead and landed on runway 06. The aircraft ran off the runway onto the grass. The pilot of VH-BFT sighted VH-TNO shortly after the collision, diverted to the left and below VH- TNO and initiated a go-around. VH-BFT eventually landed safely. Three controllers were on duty in the Jandakot control tower at the time of the accident. One controller occupied the Aerodrome Controllers (ADC) position and a second controller the combined position of Surface Movement Controller (SMC) and Coordinator (Coord). A third controller, occupying the Senior Tower Controller's position (Snr Twr), had completed a handover/takeover after coming on duty and was occupied at the rear of the tower. Circuit traffic at the time of the accident was moderate although traffic during the period immediately before the collision was heavy. In the hour before the collision, 98 movements were recorded with a further 66 during the hour of the accident. In the 12 minutes prior to the accident a disproportionate number of 44 movements were recorded. There were seven other aircraft in the circuit when VH TNO joined downwind, with six remaining at the time of the collision. Radio traffic was also very heavy during the period immediately prior to the collision. The ADC made and received 125 two-way radio transmissions during the 12 minutes preceding the accident. Having allocated a downwind sequence to the two aircraft and believing that VH-BFT's pilot's acknowledgement of sequencing instructions meant that VH-TNO had been sighted, the ADC's attention was concentrated on the other circuit traffic. During the 2 minutes 40 seconds between the ADC's last downwind call to VH-TNO and the collision there were 14 two-way transmissions. The workload and practices were such that the ADC did not observe either VH-TNO or VH-BFT again until immediately prior to the collision. The ADC had checked the runway was clear of traffic, was moving VH-TNO's flight strip and was giving its pilot a clearance to land when the impending collision was first noticed. As both aircraft were head on to the tower and the aircraft were approximately the same distance from the threshold it was not possible for the ADC to determine which call-sign belonged to which aircraft. The ADC was unable to give any collision avoidance instructions as they could have made the situation worse. Responsibility for separation in the circuit area at Jandakot rests with the Pilot's in Command of circuit aircraft. Assistance is provided by the air traffic controllers by issuing instructions for rejoining, downwind sequencing, and landing clearances. Safe separation in the circuit depends on a good lookout and on the pilot understanding controller's instructions, following those instructions and advising the controller if the instructions have not been understood or can not be complied with. In this accident the pilot of VH-BFT and the ADC, thought that the downwind sequence instruction had been understood and was being followed. The pilot's inexperience led to the misidentification of conflicting traffic, whilst a combination of workload and aircraft positions probably led to a less than adequate lookout and a failure to sight the real conflicting traffic. Although there were three controllers in the tower, circumstances, workload and the belief that the pilot of VH-BFT had sighted the conflicting traffic, prevented the developing collision from being observed, by the Tower Controllers, until it was too late.

Significant Factors:

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

1. Pilot Inexperience The pilot of VH-BFT was inexperienced in aviation and particularly in GAAP. Although instructed to follow the Cessna entering mid downwind, in front, at the 10 o'clock position the pilot identified a different aircraft, a twin of different make, in the 12 0'clock position which was on late downwind. A more experienced pilot would be expected to look for the aircraft at 10 o'clock, to know the difference between that aircraft and another on late downwind and, if it was not identified, indicate that fact to the Tower by radio. The pilot had completed a dual trip immediately prior to the accident flight and although difficulties were initially encountered with Jandakot circuit procedures the instructor's final assessment was that the pilot's procedures were satisfactory.

2. Distraction by Other Procedures and/or Cockpit Visibility Problems. An experienced pilot would be expected to sight another aircraft in front and to the left at the same height on downwind. Although the reason why the pilot of VH-BFT did not sight VH-TNO during the downwind leg could not be determined, there were three main possibilities;

(a) The pilot was concentrating on the downwind spacing from the runway, and manipulation of the aircraft controls and/or downwind checks caused a distraction which prevented a good lookout.

(b) The position of VH-TNO in relation to VH-BFT was such that the lefthand windscreen pillar prevented the pilot of VH-BFT from sighting VH-TNO.

(c) A combination of both the above.

3. Task Saturation The radio transmission traffic during the period preceding the collision was very heavy. An experienced pilot would be expected to listen to the radio transmissions to help determine the position of the traffic in the circuit. The pilot of VH-BFT had the opportunity to recognise a mistake when the pilot of VH-TNO was given downwind sequencing. Inexperienced pilots, attempting to cope with the other tasks associated with circuit flying may mentally tune out the radio traffic that does not refer to their aircraft.

4. Failure of the Safety Net The safety net, an overall safety concept, which is provided by the Tower Controllers, is dependent on the controllers having the time to carry out their sequencing, landing clearance and other tasks as well as being able to inspect the circuit for possible developing unsafe situations. The ADC, having given the pilot of VH-BFT sequence instructions and believing that they were understood and followed, was then engaged on other tasks and did not check the late downwind to final legs of the circuit again until immediately prior to the collision. The SMC/Coord and Snr Twr controllers were engaged in their own tasks and did not observe the developing confliction. Consequently, the safety net did not work.

5. Aircraft Identification Problems

(a) The position of the aircraft, in relation to the ADC prevented the ADC from being able to differentiate between the conflicting aircraft and issue collision avoidance instructions.

(b) The use of the words Cessna and twin may not have provided sufficient identification information. A Cessna can also be a twin.

Recommendations:

1. All pilot's and operators, at GAAP aerodromes, should be reminded, through the publication of this incident in either the BASI Journal or the Civil Aviation Authority (CAA) Safety Digest, of their obligations to ensure that they and/or their pilots and students understand and comply with circuit radio and operational procedures. In particular student pilots should not be permitted to operate solo in a GAAP circuit unless they are fully conversant with all the required procedures.

2. The Civil Aviation Authority should carry out a review of the operational and administrative procedures used in the Control Towers at GAAP airports with a view to improving the safety net provided by the Tower Controllers. In particular the CAA should consider the allocation of a specific task, traffic spotting, to one of the Tower Controllers. At airports where there are high traffic densities and/or there is a significant pilot training component this task may need to be allocated to an additional tower position. Subsequent to the accident a parallel runway has been built at Jandakot to relieve traffic congestion. Tower staffing and procedures have been changed to provide better ATS coverage both for the new parallel runway system and in general.

Circumstances:

Both VH-RQQ and VH-TKR reported taxying for circuits at 1500 hours. VH-RQQ was subsequently cleared for take-off from Runway 10 Left (10L) at 1508 hours. During the first circuit by VH-RQQ, a Beechcraft Skipper, VH-HBI, was cleared for take-off. VH-TKR was then cleared for take-off and instructed by the Control Tower to follow the Skipper. VH-RQQ was then cleared to carry out a touch and go landing. The pilot of VH-HBI flew a wide circuit and VH-TKR, because of the instruction to follow VH-HBI, did not turn onto the crosswind leg of the circuit until reaching 1000 ft. VH-TKR was then flown downwind at a wider spacing than normal but inside the circuit flown by VH-HBI. VH-RQQ entered downwind close behind but inside the track flown by VH-TKR. At this stage, the Tower Controller asked the pilot of VH-RQQ "confirm you're following that Cessna I think he might be out to your half right now he's fairly wide". VH-RQQ responded "yes I got him in sight".

The Tower Controller then asked, "are you going to cut inside of him or are you following him?". VH-RQQ answered "I'm trying to follow him but he's getting a bit out of oh he's turning now I'll follow him". At about this time, VH-HBI turned from the downwind leg onto the base leg of the circuit and VH-TKR reported "downwind touch and go". The controller then provided VH-TKR with sequencing instructions in relation to VH-HBI turning base. Immediately following this instruction, the pilot of VH-RQQ initiated a radio transmission which was cut short by the collision between VH-RQQ and VH-TKR. The instructor in VH-TKR said that he first saw VH-RQQ positioned behind and to the left of his aircraft at what he estimated to have been about 200 m. He looked ahead to check the position of VH-HBI and when he looked back again to check VH-RQQ, he had insufficient time to take avoiding action before the aircraft collided. The instructor took control of VH-TKR from the student pilot immediately after the collision and was able to conduct a successful landing. The right wing of VH-RQQ was severed in the collision and the aircraft fell to the ground out of control. Examination of both aircraft showed that the collision occurred while VH-RQQ was converging at an angle of about five degrees with VH-TKR and overtaking at about 15 kts. The outer portion of the right wing of VH-RQQ struck the rear of the left-wing root of VH-TKR. At the time of the accident, the wind was from the north-east at 10 kts with scattered strato-cumulus cloud at 2500 ft. There were showers well to the west and south of the airfield. Visibility was estimated to be 40 km. The position of the sun was 17 degrees to the right of the circuit downwind track and 27 degrees above the horizon. While the climb and downwind speeds of the three aircraft were of the same order, VH-RQQ had the better performance, followed by VH-TKR and then VH-HBI. Two of the aircraft (VH-HBI and VH-TKR) were flying rectangular circuits, i.e. crosswind and base legs at right angles to the runway direction. VH-RQQ, on the other hand, was flying an oval circuit in which the crosswind and base legs were flown as continuous turns, and which was shorter than a rectangular circuit. The nett effect of this was to accentuate the performance difference between VH-RQQ and the other two aircraft.

It is possible that the pilot of VH-RQQ might have assumed that VH-TKR was departing the circuit area when that aircraft climbed straight ahead after take-off to, eventually, 1000 ft. At the same time, he may have observed VH-HBI on the downwind leg and set himself to follow that aircraft. After turning downwind and seeing VH-HBI well wide on downwind, he may have had some concern over his ability to follow that aircraft. This concern could have been reinforced by the controller's transmissions relating to the "Cessna I think he might out to your half right now he's fairly wide". Analysis of the probable flight paths flown by each aircraft indicated that VH-TKR was in the region of abeam VH-RQQ when VH-RQQ began its downwind leg. It is possible that the pilot of VH-RQQ did not look in this direction when attempting to sight the "Cessna I think he might be out to your half right now he's fairly wide". Just prior to the collision, the student pilot in VH-TKR transmitted a downwind call. This call was late because of the interchange between the Tower and VH-RQQ. As a result of the downwind call by the VH-TKR, the Tower Controller sequenced VH-TKR to follow VH-HBI on base. The subsequent transmission from VH-RQQ which was interrupted by the collision could have at least two explanations. The pilot may have intended reporting mid-downwind, or he might have been seeking clarification as to the sequencing instruction just given to VH-TKR.

There was no apparent attempt by the pilot of VH-RQQ to avoid colliding with VH-TKR. He was part way through a radio transmission at the moment of collision. His voice tone at that time was normal. It is possible to conclude, therefore, that the pilot of VH-RQQ did not see VH-TKR. However, he did indicate to the Tower Controller that he had sighted and would follow "that Cessna". (VH-TKR was a Cessna, a high winged configuration aircraft while VH-HBI was low winged.) On the basis of this positive response from the pilot of VH-RQQ, the Tower Controller was entitled to conclude that VH-RQQ had sighted and would follow VH-TKR. For the pilot of VH-RQQ not to have seen VH-TKR, he must have misidentified VH-HBI as a high winged Cessna. A number of aspects could have contributed to this. Firstly, the distance between VH-RQQ and VH-HBI was calculated to have been at least two kilometres at the time the pilot of VH-RQQ reported that he would follow "that Cessna". At the same time, the sun was within a cone of about 30 degrees of the line of sight from VH-RQQ to VH-HBI.

The resulting glare could have caused reduced visual effectiveness for the pilot of VH-RQQ. Such other aspects as the contrast of VH-HBI against its background, and the complexity of the background itself, could also have limited the ability of the pilot to distinguish between a high winged and a low winged aircraft. The pilot of VH-HBI reported that he had just rolled out of the turn from downwind on to the base leg of the circuit when he heard the mayday call from VH-TKR. This indicates that VH-HBI could have entered the turn at about the time the pilot of VH-RQQ said "he's turning now I'll follow him". There were two other aircraft in the Archerfield circuit at the time of the accident which were not directly related to the incident.

These aircraft were in the final approach path to the runway when the collision occurred. It was to these aircraft that the controller's attention was directed following the response from the pilot of VH-RQQ that they had sighted and would follow the "Cessna".

General Aviation Airport Procedures (GAAP) were in operation at Archerfield at the time of the accident. Under these procedures, the Air Traffic Control responsibilities were to

1. apply runway separation standards,

2. issue instructions and/or traffic information to regulate traffic,

3. provide traffic information relating to possible conflictions inside the control zone in order to alert pilots that avoiding action may be necessary, and

4. where practicable, maintain surveillance of aircraft activity within the control zone and on the aerodrome to endure a safe, orderly flow of traffic.

Aircraft separation, other than on the runway, was not provided by Air Traffic Control. The pilot-in-command was primarily responsible for ensuring separation from other aircraft within a General Aviation Control Zone. The reason VH-TKR was instructed to follow VH-HBI was that the minimum runway separation standard (600 m) was being applied. No such direction was necessary with respect to VH-RQQ following VH-TKR as sufficient distance existed at the runway on DEPARTURE for VH-RQQ to remain separated from VH-TKR provided similar circuits were flown. Later, traffic information was provided to VH-RQQ concerning the possible confliction of that aircraft with VH-TKR and resolved to the controller's satisfaction.

In hindsight, however, the information given to VH-RQQ about the position of VH-TKR ("half right fairly wide") was possibly ambiguous and open to misinterpretation by the pilot of VH-RQQ.

Significant Factors:

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

1. Of the three aircraft directly involved in the accident sequence, two flew rectangular circuit patterns while the third, VH-RQQ, flew an oval circuit.

2. It is possible that the pilot of VH-RQQ misinterpreted the information from the Tower Controller concerning the position of VH-TKR relative to his aircraft.

3. It is possible that because of the distance between VH-RQQ and VH-HBI, the position of the sun, and the visual contrast between VH-HBI and its background, that the pilot of VH-RQQ misidentified the (low winged) VH-HBI as (high winged Cessna) VH-TKR.

4. The pilot of VH-RQQ probably did not see VH-TKR before the collision.

5. The pilot of VH-TKR did not correctly assess the threat posed by VH-RQQ when he saw that aircraft behind and to his left.

Circumstances:

VH-CZN was tracking Albury direct to the Bindook VOR at FL 350. At 0928 UTC Sydney Sector 3 Controller issued the aircraft with clearance to descend to FL190 with a requirement to reach that level by 80 DME Sydney. At 0933 UTC, the Sector 3 Controller cleared VH-TAV, which was tracking to Bindook VOR via Rugby NDB at FL330, to descend to FL200 with a requirement to reach that level by 70 DME Sydney. Because VH-CZN was about 10 miles ahead of VH-TAV, on converging tracks for Bindook, VH-CZN was No 1 in the approach sequence, VH-TAV was No 2, and a Thai B747 on the Parkes - Bindook track was No 3. At this time, Sector 3 Radar and Procedural positions were combined due to a relatively light workload. The controller who occupied the position was inexperienced. He had completed 11 shifts following training and initial rating on the Sector 3 position. VH1] CZN had an operational restriction not to exceed 250 knots IAS below 10,000 feet which was noted on its flight plan message. At 0935 UTC, VH-CZN was 130 miles from Sydney and VH-TAV was approximately 140 miles from Sydney and laterally displaced about 20 miles to the left of VH-CZN. The Flow Controller decided to reverse the arrival sequence, with VH-TAV to become No 1 and VH-CZN No 2 because of the speed restriction on VH1] CZN below 10,000 feet. The Flow Controller asked the Sector Three Controller to position VH-CZN behind VH [[1] TAV and request VH-TAV to maintain maximum speed. At 0936 UTC the Sector Three Controller instructed VH1] CZN to turn left onto heading 350 and requested VH-TAV to maintain maximum speed for as long as possible. At 0938 08 VH-TAV reported leaving FL330. Thirty-two seconds later, VH-CZN reported leaving FL350. The controller acknowledged the descent and turned VH-CZN further left onto 340. This was followed by another heading change onto 330 twenty-nine seconds later, at 0939 12. At 0939 27 VH-CZN was instructed to maintain FL 330, but the aircraft reported having left FL320. The aircraft was re assigned FL310. VH-TAV reported leaving FL315 at 0939 48. VH-CZN requested the distance from the other aircraft at 0940 21. The controller advised it was 5 miles north (of VH-CZN's position). A breakdown in the separation standards occurred. The radar recording indicated VH-CZN had passed behind and above VH-TAV. The minimum distance/height between the aircraft was two miles and 600 feet. An experienced controller was seated beside the sector Three Controller during the incident, but he did not have his headset plugged into the circuit. He suggested vertical separation be re-applied by restricting VH-CZN to FL330. This advice was misconstrued by the Sector 3 Controller as a heading change onto 330.

Significant Factors:

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

1. The Controller made an error of judgement in the assessment of an initial heading for VH-CZN to be positioned behind VH-TAV.

2. Attempts to radar vector VH-CZN to maintain lateral separation after the initial heading change were ineffective due to further poor judgement.

3. The controller did not apply procedures in a timely manner, to maintain vertical separation between the two aircraft, until after the initial vertical separation was lost.

4. The controller did not warn the crew of VH-CZN of the loss of separation standards.

5. The poor judgement by the controller indicated inadequate training and checking of the controller in radar vectoring techniques.

6. The controller was inexperienced.

7. An experienced controller seated at the Sector Three console, was unable to offer timely advice as he was not plugged into the intercom/radio circuit.

Recommendations:

The circumstances of this occurrence have been referred to the Civil Aviation Authority (Air Traffic Services) with recommendations concerning the training and checking of trainee and newly rated ATS officers.

Circumstances:

The Sydney Approach North controller was radar vectoring MAC 60193, a USAF military transport aircraft, to intercept the flight planned track to Christchurch after departing from RAAF Richmond. VH-CZC was being radar vectored by the Sydney DEPARTUREs North controller to intercept the 002 radial to West Maitland after taking off from runway 25. When it became apparent that the flight paths would conflict, the DEPARTUREs North controller was assigned the task of maintaining adequate separation between both aircraft. The minimum separation required was 1000 ft vertically, or 3 nautical miles laterally. A climb restriction was applied to VH-CZC, limiting that aircraft to an altitude of 6000 ft. This restriction was applied in anticipation of MAC 60193 reaching 7000 ft or higher before lateral spacing was less than 3 nautical miles. However, for a period of about 3 minutes, the C141 failed to climb as rapidly as the DEPARTUREs controller had anticipated, and it became apparent a traffic confliction could not be averted. Both crews were notified of the conflicting traffic and given heading changes. Visual contact was established and the aircraft passed safely clear of each other at less than the minimum required separation standard.

Significant Factors:

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

1. The DEPARTUREs North Controller attempted to provide the required separation based on an assumed rate of climb by Mac 6019 3.

2. The actual climb performance of MAC 60193 was less than anticipated.

Circumstances:

VH-HYF departed Adelaide Airport on an 'Adelaide East 2 Mildura' Standard Instrument Departure (SID), with an unrestricted climb to its cruising level of Flight Level (FL) 370, then via the 'Tango 77' route to Brisbane. Because a Boeing 747 from Melbourne would be overflying Mildura at FL 310, Melbourne had co-ordinated with Adelaide a requirement for VH-HYF to reach FL 330 by 37 km south-west of Mildura. VH-EAK was flying from Sydney to Adelaide via Mildura, cruising at FL 310. It was on the reciprocal heading to VH-HYF and appeared on the Adelaide Control radar display at 235 km from Adelaide. When VH-HYF was transferred to Adelaide Control, the controller requested that the aircraft maintain its best rate of climb to FL 330. His objective was to climb VH-HYF above VH-EAK, using radar to maintain separation instead of procedural control. This would allow VH-EAK to follow its preferred descent profile to Adelaide, and for VH-HYF not to be held at a lower level until procedurally separated with the overflying Boeing 747. Approaching FL 310, VH-HYF experienced an increase in ground speed due to a strong westerly windshear increasing the closing speed between the aircraft. While maintaining maximum rate of climb, the air speed of VH-HYF fell below the minimum manoeuvring speed. With the airspeed trend indicator fluctuating due to turbulence, the Captain reduced the climb angle to accelerate the aircraft without advising the controller of the reduction in climb performance. VH-HYF passed VH-EAK 200 km north-east of Adelaide, with 800 ft vertical and 0.4 nm horizontal separation with less than the required standard of 2000 ft vertical or 7 nm horizontal separation. VH-HYF had regained its normal rate of climb as the aircraft passed. The controller had been operating two sectors on combine, with a subsequent increase in co-ordination workload. He had monitored VH-HYF during its climb to FL 310, at which time it was 76 km to the west of VH-EAK. At its initial climb rate he expected VH-HYF should have passed FL 340 by the estimated time of passing. The controller continued his scan of the radar display. When his gaze returned to these aircraft, the noticed that the radar returns were merged, which would be normal as they passed. When the radar returns separated, the controller noted that the altitude indication for VH-HYF was showing the aircraft to be at FL 330. He therefore had no reason to believe that a breakdown in separation had occurred. A discussion had also been in progress during this period with other controllers regarding industrial matters. This situation was causing the controller considerable amount of anxiety and may have been a factor in this occurrence.

Significant Factors:

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

1. The controller applied inadequate separation standards so as not to cause inconvenience to the aircraft.

2. The controller expected that VH-HYF would maintain the same rate of climb to FL 330.

3. The controller was operating two positions on combine.

4. VH-HYF experienced windshear increasing the tailwind component and closing speed with VH-EAK.

5. In turbulent conditions the air speed of VH-HYF fell below its minimum manoeuvring speed. The Captain accelerated the aircraft, reducing its rate of climb without advising the Controller.

6. The controller's attention may have been affected by anxiety concerning industrial matters. This incident was not the subject of an on-scene investigation.

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.

Shortly after 1000 hours, VH-ANE taxiied for departure from runway 03. Prior to the aircraft being given a takeoff clearance another aircraft departed from the same runway. As a result it was necessary to turn that aircraft, to provide the required separation, prior to VH-ANE being cleared for takeoff. When the tower controller had established separation, VH-ANE was given a clearance to commence an immediate takeoff. By this time VH-RME was established on final approach for runway 03. The pilot of VH-RME then became concerned that the runway might not be available for him to carry out a landing and he commenced a go-around. The tower controller was advised immediately and he instructed VH-ANE to abandon the takeoff. VH-RME subsequently completed a circuit and landed, and VH-ANE then departed for Melbourne. The investigation revealed that at the time VH-RME commenced to go around the aircraft was about 400 feet above ground level. The tower controller responsible for the separation of landing and departing aircraft was of the opinion that the required runway separation would have been achieved had VH-RME continued with the landing.