Loss of separation

FACTUAL INFORMATION

The Australian-registered Boeing 767 (B767) had departed Brisbane on a flight to Christchurch, New Zealand and had passed the reporting point STUDA (30.18S 155.17E) at 1006 EST. The crew were maintaining the aircraft at flight level (FL) 370 on air route L503.

The foreign-registered B767 had departed Nadi, Fiji on a flight to Sydney and had passed Lord Howe Island at 1009 EST. The crew were maintaining the aircraft at FL390 on air route B450, which crossed the track of the Australian B767 approximately 90 NM south-west of Lord Howe Island.

Both aircraft were under the jurisdiction of Brisbane Air Traffic Control Sector 8. After receiving the foreign registered B767's position report at Lord Howe Island, the controller was required to forward the time estimate for the aircraft's next position report to Sydney approach control. This communication was to be carried out via a link that requires the receiving controller to depress a switch, indicated by a flashing light on the control console, in order for conversation to commence. On this occasion the Sydney controller was busy and it took almost seven minutes for the link to be opened.

There were five aircraft en-route from Australian airports to New Zealand that were under the control of the Brisbane controller. The flight times and disposition of these flights were such that several traffic separation conflictions would arise in Auckland's sector of responsibility unless corrective action was taken. At 1015, the Brisbane controller coordinated various matters with the Auckland controller and proposed some solutions which he could initiate to assist the Auckland controller in preventing the traffic conflicts. In particular, he suggested that the Australian B767 should climb to the non-standard FL390 and another aircraft climb to the non-standard FL350. The Auckland controller stated that he would consider these, and other, options before further coordination with the Brisbane controller.

At 1017, the crew of the Australian B767 requested a climb to FL390 due to turbulence. Although this was a non-standard level for eastbound flights, it did offer an immediate solution to four of the five prospective traffic conflictions. The Brisbane controller decided to approve the climb after discussing the issue briefly with the Auckland controller during a second coordination exchange, but without carrying out appropriate checks for lateral separation between the aircraft where air routes B450 and L503 intersect.

Just prior to approving the Australian B767's climb, the Sydney approach controller responded to the Brisbane controller's earlier attempt to coordinate details of the foreign B767. By this time the Brisbane controller could not recall the reason for initiating the call and the two controllers terminated the conversation without completing the intended task. The climb was approved at 1018.

At 1021, the Brisbane controller realised that he had not carried out all the required checks to ensure separation before approving the change in flight level. Although he did not make a specific scan of his flight progress strips, he was uneasy about the decision and elected to cancel the climb approval. He issued instructions for the crew of the Australian B767 to descend back to FL370.

The crew were passing FL385 on climb when they saw the other B767 some 25NM ahead and passing from left to right. They did not receive a warning from the traffic alert and collision avoidance system (TCAS).

The analysis of the radar recording was unable to establish the separation distance as both aircraft were outside radar coverage at the crossing point. Extrapolation of the last observed radar data for the Australian aircraft and the first observed radar data for the foreign aircraft, indicates that they passed with at least 25NM horizontal separation. However, as no procedural standard had been achieved, there was a breakdown of separation standards.

The Brisbane controller was working Sector 8 Radar and Sector 8 Ocean at the time of the occurrence. Together these two sectors form the Oceanic group. Workload was light to moderate during the period surrounding this occurrence. A team leader was rostered on duty but was conducting tasks outside the immediate work area at the time of the occurrence. Another controller was also rostered for duty on the Ocean group but was taking a rest break.

ANALYSIS

The Brisbane Sector 8 controller approved a change in flight level for the Australian B767 without carrying out the required checks for possible conflicts. This action may have been a result of the controller focussing his attention on resolving potential conflicts for the Auckland controller.

More specifically, the controller's omission occurred at a highly automised, skill-based level of performance. Following the Australian B767 crew's request to go to the non-standard FL390, a controller should normally undertake the following actions:

1. Check the flight strips and ensure there was no potential conflictions.

2. Communicate with relevant controllers to obtain approval for a non-standard flight level.

3. Approve or disapprove the change in flight level.

In this particular case, the controller had already discussed the possibility of a higher level for the B767 with the Auckland controller shortly before the flight crew requested the level change. When the Brisbane controller received the request, there would have been a strong, natural tendency to immediately provide this information to Auckland and therefore continue the previous conversation. Indeed, by continuing the conversation in a subsequent coordination call to Auckland just 2 minutes after the first contact, the controller had commenced his response to the B767 flight crew's request for a change in flight level. However, he had started the task at the second step in the sequence and omitted checking the other flight strips for potential conflictions.

As the request for the level change was due to turbulence, the controller may have felt some urgency to respond to the request. In addition, the Brisbane controller's awareness of the foreign B767 may have been reduced in the period prior to the occurrence. Firstly, the Sydney controller did not initially respond to the Brisbane controller's attempt to pass coordination for that aircraft. Secondly, the controller's attention was focussed on the other aircraft under his control during his discussions with the Auckland controller.

Skill-based errors, such as the one involved in this occurrence occur when a person performs a familiar task in an environment which is slightly different to that which is normal. In this case the difference was that the Brisbane and Auckland controllers were discussing a level change shortly before it was requested by the Australian B767 crew.

Skill based tasks are usually performed semi-automatically, with a low awareness of the actions taken by the individual. Reducing the incidence of such errors can be difficult due to this low level of awareness at which skill-based behaviour is performed. Airservices Australia will soon be introducing The Advanced Australian Air Traffic System (TAAATS). This new system will involve significant changes to the way many air traffic control tasks are performed. For procedural enroute controllers, a notable change will be the introduction of a display which gives a plan position indication for aircraft in their area of responsibility. This change will probably make the detection of potential traffic conflicts easier.

The likelihood of detecting and correcting such skill based errors before their consequences are significant could be improved through the introduction of an automatic conflict alert. Such an alert is currently being considered for radar tracks in TAAATS but not for other tracks. An alternative defence is the presence of other controllers to supervise or support a controller. Although there was provision for other controllers to be on duty, this defence was not present at the time of this occurrence.

SIGNIFICANT FACTORS

1. The Brisbane Sector 8 controller approved a change in flight level without carrying out the required separation calculations.

2. The Brisbane Sector 8 controller was attempting to solve future separation conflicts and may have been distracted from the immediate task.

SAFETY ACTION

As a result of this and several other occurrences, the Bureau of Air Safety Investigation (BASI) examined issues associated with Airservices Australia's operation of teams in air traffic services. This examination resulted in BASI issuing the following Safety Advisory Notice to Airservices Australia on 27 January 1998:

Safety Advisory Notice SAN 970137

Airservices Australia should take note of the safety deficiencies detailed by this document and take appropriate action.

The safety deficiencies referred to in the document were:

1. an undesirably low level of operational support provided by experienced controllers, including team leaders and other full performance controllers, to controllers working in operational positions.

2. an inappropriately low level of emphasis on team development activities, such as the provision of team leader training and support, and the regular provision of team days with structured learning content for team members.

3. performance evaluation systems for team leaders that do not ensure relevant team leader performance areas are measured, and also do not ensure that any degradation in a team leader's proficiency on operational positions will be detected.

4. an inappropriately low level of training and development for many controllers on human factors issues, particularly those associated with inter-controller coordination and communication.

A Piper Chieftain (PA31) departed Bankstown on a flight to Moorabbin in accordance with the Instrument Flight Rules. The Sydney Departures controller issued the pilot with radar vectors to intercept the Sydney-Cordo track, together with an instruction to climb to and maintain 5,000 ft. At about that time a Boeing 747 (B747) was approaching Sydney from the west, in instrument meteorological conditions, following a RIVET Standard Terminal Arrival Route. The crew had been issued with a clearance to descend to and maintain 6,000 ft. The flight paths of the two aircraft were to cross each other at approximately right angles, some 8 NM to the south-west of Sydney.

The crew of the B747 subsequently advised the Sydney Approach controller that they had received a Traffic Collision and Avoidance System Resolution Advisory (TCAS RA). The RA instruction to climb the aircraft had been followed by the crew and the aircraft reached a maximum altitude of 6,300 ft before returning to the assigned level. At that time the controller observed the radar return of the PA31 descending through 5,300 ft and queried the pilot as to his present level. The pilot replied that he was returning to 5,000 ft. Neither crew sighted the other aircraft.

Analysis of recorded radar data revealed there had been a breakdown in separation between the two aircraft. The minimum vertical separation between the B747 and the PA31 was 600 ft whilst the lateral separation was 1.7 NM. The required separation standards were 1,000 ft vertically or 3 NM laterally. The PA31 reached a maximum altitude of about 5,400 ft. The pilot of the PA31 later reported he had been distracted at the time his aircraft was approaching 5,000 ft and had subsequently climbed through his assigned level.

FACTUAL INFORMATION

The crew of a Fokker Fellowship (F28) aircraft had flight planned to conduct navigation aid calibration of the Sydney runway 16L instrument landing system (ILS). Runways 16L and 16R were nominated for arrivals and departures. The crew received a clearance for a radar departure from runway 16R. The departures controller's intention was to radar vector the F28 to the east and north of the aerodrome for an intercept of the 16L ILS from the north. The F28 departed from runway 16R, heading 170 degrees, on climb to 3,000 ft. When the F28 was 8 NM south of the aerodrome the departures controller instructed the crew to turn left onto a heading of 120 degrees, to parallel the RWY 16L departure track. The controller had six aircraft on frequency, with a number of pending departures for both runways. He planned to vector the F28 across the RWY 16L departure track between two B737s departing from runway 16L. The first B737 took off with an instruction to turn left onto a heading of 060 degrees. The F28 was also instructed to turn left heading 060 degrees. The controller assessed that the F28 could cross the RWY 16L departure track ahead of the second B737, which had also taken off, and instructed the F28 to turn onto a heading of 020 degrees.

The crew of the second B737 had earlier been issued with a West Maitland 7 SID, on climb to 5,000 ft. The SID required the aircraft to track 155 degrees until reaching 600 ft, and then to turn left to intercept the 126 degrees radial of the Sydney VHF omni-directional radio range (VOR) navigation aid. The B737 crew were subsequently re-cleared to climb to their planned level of FL210 immediately after departure. The controller observed the reducing distance between the F28 and the second B737, but believed the B737 would climb above the F28, and that the vertical separation standard of 1,000 ft would be achieved prior to the distance reducing to less than the required lateral standard of 3 NM. However, when the B737 reached 3,000 ft the crew levelled the aircraft to accelerate to 250 kts. As the nose of the B737 was lowered the pilot in command observed the F28 at the 11 o'clock position, at a distance of 1 to 2 NM and slightly below their level. Just prior to the distance between the aircraft reducing to less than 3 NM, when the vertical separation was 300 ft, the controller instructed the crew of the F28 to turn right onto a heading of 040 degrees. He then instructed the crew of the B737 to turn right onto a heading of 180 degrees. The aircraft passed with less than the minimum vertical and lateral separation standards. Aircraft departing to the north and east were normally instructed to to depart from runway 16L, if that was operationally acceptable. The F28 had been parked overnight at Sydney aerodrome on the tarmac adjacent to the threshold of runway 16R. There was no operational reason for the aircraft not to have used RWY 16L for departure.

ANALYSIS

The controller relied on his understanding of B737 performance to establish vertical separation between that aircraft and the F28. The lack of application of separation assurance techniques provided no alternative means to maintain separation when the B737 was unable to attain the expected altitude. The controller had a number of aircraft under his control and this aspect should have been a prompt for him to ensure separation was assured between aircraft. Had a clearance been issued for the F28 to depart from runway 16L it is unlikely that the incident would have occurred.

SIGNIFICANT FACTORS

1. The controller's expectation that the B737 would climb 1,000 ft above the level of the F28 before lateral separation reduced to less than 3 NM.

2. The controller's lack of application of separation assurance techniques.

3. The departure of the F28 from runway 16R when runway 16L was available meant that the F28 would have to cross the departure track of runway 16L in order to carry out its intended operation.

FACTUAL INFORMATION

NITE 01, a United States Navy F-14 aircraft, had departed from the Atsugi Naval Air Facility, Japan on an Instrument Flight Rules (IFR) plan that included an exercise within Restricted Area R116. The restricted airspace R116 was used for military exercises, the northern end of which was approximately 6NM south east of the track of the B767. The F14 pilot cancelled his IFR status during his initial climb, choosing to proceed under Visual Flight Rules (VFR) procedures.

The crew of the B767 were approaching flight level (FL) 250 while descending into Narita, Japan, when they received a Traffic Alert and Collision Avoidance System (TCAS) resolution advisory (RA) instruction to climb. During the transition from descent to climb, they saw a military aircraft passing in the opposite direction at high speed, approximately 500 ft below them.

At approximately the same time, the air traffic controller observed radar returns from a VFR aircraft departing R-116 at FL250 and passed this information to the crew of the B767. He also contacted the pilot of the F-14 to establish that pilot's intentions. The B767 was climbing through FL255 (approximately) when the military aircraft passed.

The rules for VFR flight in Japanese airspace were such that a pilot could choose to conduct a flight using a 500 ft separation standard up to FL290 without an airways clearance, provided a listening radio watch was maintained on air traffic control frequencies. These procedures allowed the pilot of the F-14 to leave R-116 under VFR and maintain his own separation, of at least 500 ft, from the B767. He stated that he had the B767 in sight and was listening on the control frequency. Therefore, he had complied with the 500 ft separation standard for VFR flight below FL290.

The aircraft passed with approximately 500 ft vertical separation and no appreciable horizontal separation.

ANALYSIS

The TCAS advice to the B767 crew was a genuine alert as the respective flight paths were within the envelope for a RA alert. In this case, the crew manoeuvred their aircraft to a comparatively safe altitude, allowing the military pilot to pass beneath their aircraft.

SAFETY ACTION

As a result of the investigation, the Japanese Civil Aviation Bureau has requested the United States Air Force (the body responsible for overall military operations in the area) to remind all pilots under their jurisdiction of the proximity of IFR air routes and of the general civil airspace structure, and also to remind their pilots of the requirement to maintain adequate separation from civil aircraft.

Additionally, the Japanese Bureau has asked for military training to be kept, as much as possible, within the specified training areas.

FACTUAL INFORMATION

The crew of an instrument flight rules (IFR) Saab 340 operating a flight from Sydney to Canberra had received an airways clearance for a Shelleys 5 standard instrument departure (SID) on climb to 3,000 ft. The SID required the crew to track on a heading of 335 degrees magnetic (M) and to turn on to a heading of 210 degrees M when they reached 600 ft on climb. The Saab taxied for an intersection departure for runway (RWY) 34L from taxiway B10 and stopped at the holding point awaiting departure approval. This taxiway was on the eastern side of the runway and approximately 1450m north of the threshold.

The traffic flow was busy when the aerodrome controller west (ADCW) received departure instructions from the departure south radar controller (DEPS) for a Bell 206 (B206) helicopter. The B206 was to depart from the helicopter area to the east of RWY 34/16 to Bankstown, located approximately 10 NM west of Sydney aerodrome. The planned altitude for the B206 was 1,500 ft. The ADCW cleared the pilot in command (PIC) of the B206 to take-off. The PIC of the B206 was approved to cross RWY 34L behind a landing Boeing 747 (B747). At the same time the ADCW approved two taxiing Boeing 737s (B737) to cross RWY 34L at taxiway J which was parallel to and south of B10. After departure the ADCW instructed the PIC of the B206 to change to the DEPS frequency.

The next aircraft in the landing sequence for RWY 34L was a B737. The ADCW estimated that there was sufficient time for the Saab to depart prior to the B737 reaching the runway. The ADCW requested and was granted departure instructions for the Saab by DEPS. As the approaching B737 passed a position approximately 2 NM from the threshold of RWY 34L the ADCW cleared the crew of the Saab for immediate take-off after confirming that they were ready for an immediate departure.

As the Saab accelerated the B737 was on a close final approach. The ADCW was required to provide a landing clearance to the crew of the B737 or instruct the crew to go around if the runway was obstructed. The ADCW cleared the crew of the B737 to land. As the B737 touched down the Saab was approximately 1,700 m further along the runway and travelling at a slightly lower groundspeed than the B737. At the time the Saab became airborne the distance between the aircraft was approximately 1500 m. The B737 landed while the Saab was on the runway.

As the Saab became airborne DEPS called ADCW to coordinate a change of track and level for the previously departed B206. The ADCW approved the changes. At the suggestion of DEPS the ADCW instructed the crew of the Saab to cancel the SID and to maintain runway heading. This was done to maintain separation between the B206 and the Saab. There had been a lack of provision of separation between the aircraft.

Runway separation standards

The ADCW was required to provide the crew of the B737 with landing or go-round instructions before that aircraft reached a height of 200 ft above the landing threshold. Runway separation standards required that landing aircraft should not be permitted to cross the runway threshold until a preceding departing aircraft (less than 136,000 kg maximum take-off weight) was airborne. Controllers were required to consider the effect of aircraft carrying out a go round and the implications for separation with other aircraft.

Technical crew

The B737 co-pilot was the handling pilot for the landing. The crew could not recall if the Saab was airborne or still on the runway when they landed. The provision of a landing clearance to the crew of an aircraft entitled the PIC to continue with the landing if it was deemed safe to do so, or to conduct a go round if the situation was not considered to be safe.

Separation responsibilities between ADCW and DEPS

The ADCW was responsible for controlling arriving and departing aircraft for RWY 34L and was jointly responsible in conjunction with DEPS for separating aircraft in the airspace to the west of RWY 34L.

The ADCW and DEPS did not establish which controller was to coordinate the separation between the B206 and Saab or the type of separation to be used. Both these aspects needed to be coordinated prior to departure instruction being issued and the crew receiving a take-off clearance.

When the ADCW requested departure instructions for the Saab, DEPS assumed that the aircraft would be cleared for take-off after the B737 landed. Consequently, DEPS did not query the ADCW regarding the separation of the B206 and the Saab.

Runway usage

The ADCW believed that there was an opportunity to utilise the northern portion of RWY 34L for the departure of the Saab while the two B737s crossed the runway. This required the ADCW to confirm with the crew of the Saab that they were ready for an immediate departure, to obtain departure instructions from DEPS and to issue the take-off clearance to the crew of Saab prior to the approaching B737 requiring a landing clearance.

As the ADCW issued the take-off clearance to the crew of the Saab the B737 was approximately 2 NM from the threshold of the runway. Aerodrome controllers generally accepted 2 - 3 NM as the point at which the runway should be vacated by other traffic to ensure that an approaching B737 or similar type aircraft could be assured of a landing.

The Saab accelerated slower than the ADCW expected. The ADCW appreciated that runway separation was unlikely to be maintained between the Saab and the B737. Faced with the decision to either approve the B737 to land or to instruct the crew to conduct a go around the ADCW believed that the better option was to clear the aircraft to land. He believed that this option was the safer alternative under the circumstances.

Air traffic service performance

The ADCW felt a degree of pride in his ability to perform tower control duties. He endeavoured to provide minimum disruptions or delays to aircraft.

ANALYSIS

The ADCW's desire to not unduly delay aircraft probably caused him to attempt to facilitate the departure of the Saab at a time when there was little or no margin to compensate for delays in crew reaction to instructions or differences in individual aircraft performance.

It was unlikely that there was sufficient time for the Saab to depart as the arriving B737 had passed the position on the approach used by aerodrome controllers as a guide to assist them in managing runway usage.

The ADCW was left with limited options to resolve the situation. Subsequently, he issued a landing clearance to the crew of the B737 and allowed the crew of the Saab to continue the take-off.

His desire to provide a service to aircraft may have caused him to act hastily and consequently overlook the need to coordinate the provision of separation between the B206 and the Saab after departure, and to miscalculate the runway separation between the Saab and the B737.

DEPS and the ADCW had a shared responsibility to ensure separation was maintained between departing aircraft. However, DEPS incorrectly assumed that the ADCW would not clear the Saab for take-off before the B737 landed. DEPS should have queried the ADCW as to his plan to maintain separation between the B206 and the Saab when the ADCW requested departure instructions for the Saab. Subsequently, it was only the action of the B206 PIC requesting an amended route and level that prompted DEPS to eventually query ADCW and for the potential conflict to be resolved.

SIGNIFICANT FACTORS

1. The ADCW did not coordinate with DEPS for the maintenance of separation between the B206 and the Saab.

2. The ADCW did not ensure that separation would be maintained between the B206 and the Saab prior to issuing the crew of that aircraft with a take-off clearance.

3. DEPS did not query the ADCW with regard to the position of the B206 when the latter requested departure instruction for the Saab.

4. The ADCW did not allow for a sufficient margin between the arriving B737 and the departing Saab to compensate for differences in aircraft performance.

VH-RJE was tracking inbound on a VFR flight from Rockhampton via Charon Point (CHP), on a bearing of 143 degrees from Mackay. When the aircraft was about 35 NM from Mackay, the Brisbane Sector 7 controller provided information on the flight to the Mackay tower co-ordinator. When the co-ordinator created a flight progress strip for the aircraft the tracking details were incorrectly inserted as being via Shute Harbour, a bearing of 328 degrees from Mackay. This information was available to the aerodrome controller when the aircraft reported at 33 NM from Mackay at 4,500 ft. No other position information was provided by the pilot, nor did the controller request any. A clearance to enter controlled airspace and to track direct to Mackay at 4,500 ft was issued.

VH-TNU taxied at Mackay for Rockhampton and was cleared to track direct to Rockhampton, on the 143 radial. VH-RJE requested descent and was cleared to 3,000 ft. VH-TNU reported having left 1,700 ft on climb to FL150 and was transferred to the sector 7 frequency. VH-RJE was then asked to report crossing the coast. (The aerodrome controller expected the aircraft to cross the coast about 12 NM from Mackay on the Shute Harbour track.) The pilot reported that he was over land and approaching Hay Point (about 9 NM SE of Mackay). After the controller confirmed this position he immediately informed the sector 7 controller of the confliction with VH-TNU.

In the meantime, the sector 7 controller had observed VH-RJE on radar and was seeking confirmation of that aircraft's altitude.

By the time VH-TNU had passed 4,000 ft on climb, lateral separation between it and VH-RJE was 4 NM. Although VH-RJE had been displayed on radar to the sector 7 controller prior to this time, it had not featured in the controller's planning as it was outside controlled airspace.

For aircraft flying between Rockhampton and Mackay, laterally separated tracks had been developed. VH-TNU had planned via the western route but was given the direct track. VH-RJE had planned and tracked via the direct track.

A Cessna 152, VH-XPG, was sequenced for landing on runway 12 at the same time as a Boeing 747, VH-EBY, was sequenced for runway 15. A separation breakdown occurred when both aircraft converged towards their respective runways and the Cessna 152 was instructed to go around.

The approach radar controller had previously co-ordinated the landing of XPG on the non-duty runway 12. The aircraft's position in the landing sequence had not been determined, but would be close to that of EBY. From the aerodrome controller (ADC) position, XPG was radar observed just inside 4 NM final for runway 12 as the pilot of EBY contacted the tower at 6 NM final for runway 15. XPG was not on tower frequency; the expectation being that the aircraft would sequenced (by approach) to land behind EBY.

With EBY at approximately 2 NM final, XPG was continuing the approach at approximately 1 NM final and the pilot was not yet in contact on the tower frequency. An attempt was made to establish whether the pilot of XPG was on the tower frequency, and this proved negative. Instructions were then issued to the approach controller to send XPG around immediately. Traffic advice was issued to the pilot of EBY as the pilot of XPG made the missed approach.

The approach controller did not ensure that separation was maintained between EBY and XPG when the latter was cleared to leave the western VFR route on a visual approach for runway 12.

The approach controller should have arranged for the provision of visual separation by the ADC or issued instructions to establish and maintain lateral separation between the two aircraft prior to radar separation reducing to less than the standard of 3 NM.

The controller did not appreciate the implications for maintenance of separation when he cleared the pilot of XPG to track for final for runway 12 and to make a visual approach. The controller became distracted with other traffic considerations and did not maintain an adequate scan of the radar display. The flow controller had been advised of the inclusion of XPG in the traffic sequence.

The flow controller was satisfied that XPG could be included in the traffic sequence without detriment to other aircraft; subject to the approach controller providing final sequencing. The approach controller did not ensure that adequate separation and sequencing was applied between the two aircraft.

Cairns ATS is developing amended flow/sequencing instructions which will include procedures for aircraft arriving to either runway 15 or12, or the runways concurrently.

FACTUAL INFORMATION

An instrument flight rules (IFR) Cessna 310 (C310) departed South Grafton for Kempsey on climb to 7,000 ft. The pilot in command (PIC) had originally planned to operate from South Grafton to Coffs Harbour and then to Kempsey. He had advised flight service (FS) of the amended plan prior to departure. FS had passed the amended flight plan details to Coffs Harbour tower. The operator at the FS position responsible for the area had recently conducted a handover/takeover. Two FS areas were combined on the console. This was normal practice when traffic numbers reduced to a level that could be managed by a single operator. Traffic was light to moderate across the combined areas. The PIC of the C310 reported a departure time of 20 (0820 UTC) and on climb to 7,000 ft to the FS operator. The departure report transmission was the first to be received by the FS operator on this shift and he was unable to clearly hear the departure report. He increased the air-ground volume and requested the PIC of the C310 to confirm the aircraft's planned level. The FS operator did not request the PIC to repeat the departure report. The FS operator believed the departure time was 12 after he checked the console clock to confirm the time. He then annotated the flight progress strip (FPS) departure box for the flight of the C310 with 12. (The console clock was adjusted and operating correctly and these transmissions were made at a time when the clock would have displayed 0821.)

The FS operator co-ordinated the departure time and level for the C310 with the aerodrome controller (ADC) at Coffs Harbour tower. Based on the departure time of 0812 and the time interval for the flight of the C310, the FS operator calculated that the aircraft's estimate for Kempsey was 0838. The ADC had the same estimate, based on the departure report from the FS operator. The aircraft's actual estimate, based on the correct departure time of 0820, was 0846. The ADC was responsible for providing separation between IFR aircraft in controlled airspace (CTA) from ground level to 10,000 ft. Coffs Harbour tower controllers used visual and procedural methods to separate aircraft in CTA. There was radar coverage down to approximately 6,000 ft in the vicinity of Coffs Harbour, but there was no radar display installed in the tower. Radar was used by controllers located in Brisbane for separation in the CTA above 10,000 ft in the Coffs Harbour area. The track of the C310 crossed the CTA steps to the south-west of Coffs Harbour and the PIC required a clearance from the ADC. While co-ordinating the departure from South Grafton, the FS operator asked the ADC if he required the PIC to transfer to the Coffs Harbour frequency immediately.

The ADC suggested that the PIC remain on the FS frequency. The Aeronautical Information Publication (AIP) states that "Except in special circumstances, pilots of aircraft are required to comply with the radio communication requirements appropriate for the "Classes of Airspace-Services and Requirements" table. The table indicates that the pilot of an IFR aircraft operating outside controlled airspace (OCTA) must report to air traffic control, prior to entering CTA, and request a clearance. The PIC had conducted similar flights and had transferred to the ADC's frequency to obtain a clearance through controlled airspace. Therefore, he was expecting to transfer to the ADC frequency when the aircraft was west of Coffs Harbour. There was no equipment limitation or other reason for the PIC of the C310 not communicating directly with the ADC. The ADC issued a clearance for the aircraft to track from Grafton to Kempsey at 7,000 ft and requested the FS operator to advise him when the PIC required descent. The FS operator issued the clearance to the PIC. The PIC readback the assigned level and queried the FS operator regarding when to transfer to the Coffs Harbour frequency.

The FS operator advised that there was no requirement to transfer frequency at this stage and requested the PIC to advise the aircraft's descent point. A short time later a new operator assumed responsibility for the FS position. The PIC of the C310 requested a change of level to 6,000 ft and the FS operator co-ordinated the change in level with the ADC. The ADC recleared the C310 at 6,000 ft and this clearance was issued by the FS operator. The PIC reported that the aircraft's descent point was 26 NM by distance measuring equipment (DME). The FS operator advised the ADC of the aircraft's descent point. The ADC was expecting a BAe146, operating a regular public transport flight, to taxi at Coffs Harbour for departure and assessed that the flight may conflict with the C310. The ADC asked the FS operator "Where is he now please" (meaning the C310). The FS operator, in turn, requested the PIC of the C310 to report his DME distance. The PIC advised that the aircraft was at 19 DME. This distance was consistent with the expected position of the C310 based on the incorrect departure time and estimate for Kempsey.

The ADC believed that the aircraft was to the south-west of Coffs Harbour. The ADC issued a clearance for the C310 to leave the CTA on descent, which was relayed by the FS operator to the PIC. The aircraft's actual position was to the north-west of the aerodrome, outside controlled airspace and approaching the CTA steps. The BAe146 had planned to Sydney and the intended track crossed the track of the C310 approximately 17 NM south-west of Coffs Harbour. The ADC co-ordinated a departure clearance for the BAe146 with Brisbane Sector 15 (SEC15) and advised the controller that the aircraft would depart at 36. The SEC15 controller issued departure instructions to the ADC and the crew of the BAe146 was subsequently issued a clearance to depart Coffs Harbour on climb to an amended level of FL160. Using procedural control, the ADC was required to issue instructions to the crews of aircraft to establish and maintain either a lateral, vertical or longitudinal separation standard. There were a number of procedures which could have been used by the controller to separate the C310 and the BAe146. The BAe146 departed and the crew reported their departure to the ADC. The SEC15 controller contacted the ADC and advised him that there was an aircraft on radar to the southwest of Coffs Harbour at 16 NM, that had just entered the CTA step. The radar display had displayed a secondary surveillance radar (SSR) code 2000 squawk indicating that the unknown aircraft was at 6,000 ft. The SEC15 controller asked the ADC whether he was aware of any other aircraft.

The ADC advised that he was aware of a C310 estimating Kempsey at 38, and as the time was then 38, the C310 should be OCTA. The ADC then requested the crew of the BAe146 to report their level. The crew reported that the aircraft had left 7,000 ft. There had been no instructions by the ADC to establish a lateral or time standard to separate the aircraft. The BAe146 had passed through the level of C310 while both aircraft were in the area of conflict. There had been a breakdown of separation. ANALYSIS It was probable that the FS operator did not hear the departure time and estimated the time incorrectly after checking the console clock. The operator's misreading of the clock may have been due to the similarity of the last two digits and the transposition of the "2" and "1". He only requested the PIC to repeat the aircraft's intended level and consequently missed an opportunity to confirm the departure report. Had the FS operator requested the PIC to repeat the entire departure report it was likely that the error would have been detected. The ADC sought to establish the position of the C310 through the FS operator. However, the ADC did not explicitly request "the pilot to report position". The ADC used imprecise and non-standard phraseology to the FS operator. Had the ADC used standard phraseology it was likely that the FS operator would have requested and obtained a position report from the pilot consisting of a distance and direction from Coffs Harbour. This information would have clarified the position of the C310 for the ADC. Consequently, he would have issued instructions to maintain separation. However, the report of "19 DME" from FS confirmed the ADC's expectation that the C310 was to the south-west of Coffs Harbour, approaching the descent point and would be shortly leaving CTA. The FS operator requested a DME distance from the PIC when the ADC asked where the aircraft was. By inference, the request was for a position report; yet the FS operator reduced the request to one element of a position report.

Consequently, another opportunity was lost to compare the actual and expected positions of the aircraft. The PIC was prepared for and expected to change frequency from FS to Coffs Harbour Tower frequency to obtain a clearance. Had the FS operator and the ADC operated in accordance with standard procedures; the PIC would have transferred to the tower and communicated directly with the ADC. This would have reduced the possibility of the misunderstanding of the position information requested by the ADC from the pilot. If the PIC had transferred to the tower frequency it is likely that the ADC would have requested the PIC to either report leaving CTA, or a level or a DME distance that would have established the aircraft OCTA, before clearing the crew of the BAe146 to depart. Alternatively, the ADC would have assumed that they were both in CTA and would have issued appropriate instructions to separate the aircraft. Either of these measures would have ensured the two aircraft remained separated. The operation of the SSR transponder in the C310, and the consequent display and the recognition of the symbol on the Brisbane sector radar display, by the controller, provided an increased level of safety for the air traffic system.

SIGNIFICANT FACTORS

1. The FS operator misheard the departure report and did not request the PIC of the C310 to repeat the report.

2. The FS operator misread the console clock.

3. The ADC did not use correct phraseology when requesting the position of the C310 from the FS operator.

4. The FS operator did not request the PIC to "Report position".

5. The FS operator and the ADC did not follow standard operating procedure when they agreed to leave the PIC of the C310 on the area frequency.

Circumstances

Both aircraft were outbound from Cairns on the same track and on climb to FL 330. VH-TJD was about 9 NM behind VH-CZI. When CZI was transferred to Cairns Arrivals frequency, the crew advised that the aircraft would be cruising at reduced Mach 0.65. The controller, who had not previously experienced such a situation, did not associate this information as having any influence on the climb performance of the aircraft. He believed that because the aircraft were approximately co-speed, separation was assured throughout the climb. As CZI climbed above about FL250, the Mach Number restriction to that aircraft began to take effect and a groundspeed differential developed between it and TJD. There was other traffic in the area at the time, with the labels for these aircraft reducing the information available to the controller concerning the separation of CZI and TJD.

The aircraft were transferred to the next sector (7V) when CZI was passing FL 280. By this time, the groundspeed of TJD was 425 kts, and of CZI, 368 kts. Horizontal separation was about 6 NM and reducing. The sector 7V controller instructed CZI to maintain FL280. The crew advised that they had passed that level but would return to it. TJD then reported leaving FL297.

Examination of the recorded radar data revealed that radar separation reduced to a minimum of 4.8 NM. At the time, CZI was at FL287 and TJD at FL297. The required separation standard was 5 NM laterally and 1,000 ft vertically.

Information from the Cairns Arrivals controller, and other experienced controllers, indicated that the effect of reduced Mach No climbs on aircraft performance was not fully appreciated. Local management reported that controllers had been rebriefed on this issue.

FACTUAL INFORMATION

A Piper Chieftain registered as VH-HVA (HVA) had been flight planned to operate a flight from Maitland to Sydney at 6,000 ft. Another Chieftain registered VH-TXK from the same company was planned to conduct a flight from Gunnedah to Sydney at 7,000 ft. There was approximately 15 degrees between the inbound tracks of the two flights and their respective flight times and estimated time of departures indicated that they would arrive at Sydney at about the same time.

The two aircraft departed and were approaching Sydney when the pilot of HVA reported his position to the Departures North controller (DEPN). The pilot advised that the aircraft was 44 NM north of Sydney, and he was requesting an airways clearance. The secondary surveillance radar (SSR) transponder replies for HVA were not being received and that aircraft was not displayed on the DEPN radar display. DEPN misheard the transmission and assumed that the clearance request was from the pilot of TXK, which was displayed on the controller's radar display. The radar display indicated that this aircraft was 60 NM to the north-west of Sydney. This was a difference of 16 NM from the distance reported. DEPN issued a clearance for TXK to enter controlled airspace at 7,000 ft. The pilot of HVA believed this clearance was in response to his request and acknowledged the clearance but incorrectly read back the level as 6,000 ft. DEPN did not challenge the read back by the pilot of the incorrect level.

Approximately two minutes later, the pilot of TXK requested from DEPN a clearance to enter controlled airspace. DEPN re-issued the clearance at 7,000 ft. The pilot of that aircraft correctly read back the clearance.

The flow controller was concerned that HVA was not being displayed on the radar and requested the DEPN controller to attempt to contact that aircraft. DEPN transmitted to HVA and after receiving a reply from the pilot, requested the latter to change the aircraft's transponder code. This new code was observed on the display approximately 13 NM north of Sydney and 2.2 NM from the symbol for another aircraft at 6,000 ft. The required horizontal separation standard was 3 NM. There was a breakdown of separation.

The Sydney terminal radar consists of two radar systems; a primary radar with a range of 50 NM and an SSR which has a range of 250 NM. Consequently, aircraft with an inactive or unserviceable SSR transponder more than 50 NM from Sydney airport were not displayed. Pilots were required to check that an aircraft transponder was receiving and replying to an SSR. The pilot of HVA checked the transponder in flight and believed that the system was operating as he approached Sydney controlled airspace.

The callsigns of the two aircraft were distinctly different but some transmissions were truncated or clipped which made reception of the broadcasts difficult.

One of the methods available to a controller to identify an aircraft on radar was to correlate the observed and reported positions. When using this method a controller was required to ensure that the observed position was within the navigation tolerance of the reported position. The DEPN controller had other means available to him to identify an aircraft on radar. The investigation was unable to identify the radar identification method used by the controller.

ANALYSIS

The DEPN controller missed an opportunity to confirm the identification of the aircraft requesting a clearance when he did not correlate the observed radar position, of what he believed was TXK, with the actual position provided by the pilot of HVA. The difference between the positions was approximately 16 NM. This disparity in the positions could have alerted the controller to the possibility of a misidentification. However, the controller did not use this information to assist in the identification of the aircraft.

The pilot of HVA had an expectation of receiving a clearance from DEPN following his request. This expectation led him to believe that the clearance issued was for his aircraft, despite the clearance being prefixed with a different callsign and not at his planned level.

The pilot's subsequent read back of the incorrect level was not recognised by DEPN and the misidentification of the aircraft remained undetected.

The reason for DEPN not observing and querying the primary radar symbol from HVA was not ascertained. Similarly, the reason for the eventual operation of HVA's transponder was not ascertained.

SIGNIFICANT FACTORS

1. DEPN did not observe the primary radar symbol from HVA while the aircraft was within 50 NM of Sydney.

2. The SSR label for the HVA was not displayed on the controller's radar.

3. The controller did not correlate the pilot position report of HVA with the observed radar position on the display.

4. The pilot of HVA acknowledged and read back the clearance incorrectly.

5. DEPN did not challenge the incorrect level read back from the pilot of HVA.