Loss of separation

Pitch Black 96 operating procedures included a general exclusion of military activities in R244 above FL 290 unless acting in accordance with specific air traffic control instructions.  This exclusion was designed, amongst other things, to protect transiting civil air traffic.  DOGSTAR formation had no such air traffic clearance or instruction.

At 1535 CST and when approximately 32 NM south-east of Tindal aerodrome, the crew of the A340 reported a TCAS traffic advisory on unidentified aircraft crossing from left to right about 3 NM ahead and descending from a level approximately 800 ft above them.

Tindal centre were unable to immediately determine the callsign and flight details of the unidentified aircraft and coordinated with the Control and Reporting Unit (CRU) which would have had prior information on exercise aircraft.  The CRU were also unable to immediately identify the aircraft.

The crew of the A340 then saw the other aircraft and reported that they were twin tailed fighters.  They watched as the military aircraft passed in front of their aircraft at approximately the same level. No evasive action was required as they were able to monitor the progress of the formation clear of their projected flight path.  Shortly after, Tindal centre confirmed that the formation had been identified as DOGSTAR and that they were now under Tindal control and clear of the A340.

Radar analysis indicated that DOGSTAR formation passed at a distance of 4.9 NM in front of the A340 and had descended from approximately FL 363 to a level below the A340 during the period of the TCAS alert.  It also established that the occurrence happened in airspace between 25 and 33 NM from Tindal.

The appropriate separation standard in this airspace was either 3 NM horizontally or 2,000 ft vertically. This standard can only be provided when certain pre-conditions are met.  Some of these requirements were that both aircraft are radar identified, and both aircraft shall be on radio frequencies currently in use for radar control. These pre-conditions were not met in this case.  There was also a procedure where the CRU is allowed to provide a separation service in conjunction with the military air traffic controller in military restricted airspace, however, the pre-conditions for this procedure were not met.

Whereas the proximity did not reduce below the 3 NM criteria, a breakdown of separation did occur because the military aircraft were not operating under air traffic control instructions and were not in contact with either air traffic control or the CRU at the time of the occurrence.  Therefore, the terms and conditions set out in the Manual of Air Traffic Services for such a separation standard had not been met.

The crews of the F-15 aircraft had chosen to maintain a higher-than-normal altitude for their initial recovery track because of other exercise traffic involved in air-to-air refuelling in the vicinity of their formation.  They then obtained a radar "lock-on" on the A340 and, believing it to be another military aircraft returning for a recovery, positioned their aircraft to be number one in the recovery sequence.

ANALYSIS

The procedures set down for military exercise "Pitch Black 96" contained restrictions and requirements designed to ensure the protection of transiting civil aircraft. On this occasion, a pair of fighter aircraft contravened the procedures by maintaining an altitude above that approved, without informing either air traffic control or the CRU. This resulted in the aircraft flying in controlled airspace for approximately 60 track miles without an airways clearance and without being subject to a positive separation service.  It also resulted in a civilian aircraft not receiving a guaranteed separation service from the military formation.

SIGNIFICANT FACTOR

The crews of the military formation contravened the published procedures for military exercise "Pitch Black 96".

SAFETY ACTION

The military authorities immediately suspended the exercise and reviewed the safety procedures.  Local amendments were instigated before the exercise was allowed to continue.

FACTUAL INFORMATION

Sequence of events

An Aerospatiale AS350B (AS50) helicopter had been hired by the Civil Aviation Safety Authority (CASA) to perform a flight test of a recently installed precision approach path indicators (PAPI) system. The airport owners, the Cairns Port Authority, had asked CASA to conduct the tests as part of the acceptance procedure prior to the commissioning of the pilot-interpreted approach aid. The PAPI site was located clear of the sealed runway surface but within the runway strip.

A CASA pilot had submitted the flight plan to air traffic control (ATC) via a phone call direct to the Cairns ATC Centre using a number that was provided for the notification of local flights. This procedure did not require flight planning via the regional briefing office in Brisbane.

The helicopter had been hired on the morning of the occurrence and there was insufficient time for the CASA pilot to be rated for solo flight in accordance with company procedures. Therefore the helicopter was operated by a company pilot as pilot in command with the CASA pilot as co-pilot. The CASA pilot briefed the company pilot as to the requirements as each test run transpired.

Runway 15 was the duty runway, and the crew of the helicopter commenced operations by testing the runway 15 PAPI system, conducting several runs to the runway centreline. On each occasion the helicopter landed on the runway, even though some parts of the approach were conducted off the centreline. After landing, the crew air-taxied the helicopter to a position near the PAPI site and conducted briefings with the ground party to ascertain their requirements for future runs. These manoeuvres sometimes resulted in the helicopter being held clear of the runway strip, but on occasions it remained within the strip boundaries. Other runway movements took place during this time, including periods when the AS50 was within the runway strip.

After completing the runway 15 tests, the crew were asked to hold away from the aerodrome while a B727 departed. They were then cleared by ATC to land on runway 33 to initialise the global positioning system (GPS) equipment with the ground party prior to commencing the runway-33 PAPI flight tests. The brief to ATC had indicated that the crew would require an approach to the centreline and then position the helicopter abeam the PAPI site, but remaining on the centreline, for initialisation. The crew entered a hover in this position, approximately 2 ft above the runway.

A Cessna 182 (C182) had just completed a parachute drop and the pilot had been instructed to make a visual approach to runway 15. He had continued this approach until over the runway threshold when, as no landing clearance had been issued by ATC, he reported short final. The aerodrome controller (ADC) then gave a landing clearance. The pilot then requested permission to "land long" to facilitate taxi to his company apron. This request was approved by the ADC. The crew of the helicopter heard these transmissions but elected not to question the ADC as they were unsure of the runway being used by the C182.

As the pilot of the C182 was about 20 ft above the runway surface and about to flare, he noticed the helicopter approximately 100 - 150 ft in front of him and commenced a go-around. The C182 passed immediately above the AS35 and came within 15 ft of that helicopter.

Both aircraft subsequently completed their operations without further incident.

Flight test requirements

The Cairns Port Authority had conducted several meetings with CASA's Cairns District Office in the months preceding the test flight regarding the requirements for a flight test of the PAPI systems. On 21 June 1996, the Cairns Port Authority had written to the Cairns District Office requesting the flight test be conducted on Monday 22 July 1996 and specified the personnel and equipment that they would provide. This date was agreed by the Cairns District Office.

At 1000 EST on the morning of the flight, the Cairns Port Authority contacted the Cairns District Office to inquire about the final arrangements. None had been made. A Canberra based CASA pilot was in Cairns on unrelated CASA business and, at approximately 1130, was asked to conduct the test flight. Shortly after, arrangements were made for the CASA pilot and a member of the CASA ground party to provide a general briefing prior to a scheduled departure of 1500. No ATC representatives were asked to attend this briefing.

Flight planning

The team briefing was given at about 1500, after which the CASA pilot phoned Cairns ATC and submitted a verbal flight plan for a local flight. This included information of a generally non-precise nature such as the requirement to make several runs from 2,000 ft and approximately 4 NM, and the need to initialise the GPS while hovering on the runway next to the PAPI sites. The pilot stated that he informed ATC of the need to make each approach to the runway centreline and of the possible requirement to use the runway strip after landing. Although all parties agreed that such a conversation did take place, the investigation was unable to obtain evidence of the exact details contained in the flight plan notification.

A CASA ground party member had, in the month preceding the flight test, obtained a sample flight plan from the Melbourne-based flying unit. This plan detailed the procedures and requirements to conduct such a flight test.

No written flight plan was submitted.

Air traffic control

There were five controllers in the tower at the time of the occurrence. A rated ADC had controlled the initial runway-15 PAPI checks and had instructed the crew of the helicopter to track towards runway 33 and then handed over to a rated ADC who was undergoing familiarisation following a period of leave. The current ADC remained at the console supervising the familiarising ADC and, although feeling a little tired, considered himself fit to undertake the task.

The familiarising ADC issued a clearance for a B727 to depart and then cleared the helicopter to land. In doing so, he wanted to refer to the PAPI site in his transmissions but became confused as to the name of the PAPI during his instructions to the helicopter crew. Consequently the supervising ADC moved away from the console and picked up the instructional material on the equipment for the familiarising ADC to read. The helicopter then landed on the centreline, next to the runway 33 PAPI site, and commenced initialisation. Both ADCs were then of the opinion that the helicopter had manoeuvred to a position outside the runway strip markers, even though the clearance to land authorised the crew to use the runway and runway strip. No transmission clarifying this situation was made.

As the familiarising ADC was reading the PAPI documentation, the pilot of the C182 reported short final. The ADC looked up, saw the C182 over the threshold, made a quick scan of the runway and, believing the helicopter to be clear of the runway strip, issued a landing clearance. He then approved the long-landing request because there were no other aircraft needing to use the runway.

The pilot of the C182 then reported that he was going around due to a helicopter on the runway.

Neither ADC saw the C182 until the pilot reported short final because its approach had been across the setting sun, which severely restricted their observations in that sector. They had used the radar to monitor its position relative to the aerodrome. All the controllers thought that the helicopter had operated outside the runway strip markers during its work on the runway-15 PAPI site, even though the initial approach was on the centreline.

Although the two ADCs believed that the helicopter was hovering outside the markers, some of the other controllers believed that the helicopter was within the runway strip. They were each attending to their own tasks at the time and did not look specifically at the runway until after the clearance for the C182 to land long was given. Although two of the controllers saw what they considered to be a conflict, they had insufficient time to speak before the pilot of the C182 had commenced his go-around.

The flight progress strip for the helicopter was in the sequence bay at the ADC console, a position that indicated authorisation for the use of the runway.

Meteorological information and tower location

The incident occurred at approximately 1730, when the sun was low on the horizon and the sun shields in the tower were deployed to minimise the effect of the brightness. This situation made it difficult to see the C182 as it made its turn onto final and the controllers did not see the aircraft at all until short final.

There were many areas of shade and sun covering various parts of the runway, but the position of the helicopter was such that it was in one of the better situations for sighting purposes. However, the comparatively low aspect of the control tower cabin, when combined with the hover height of 2 ft, enabled the ADCs to see grass from the far side of the runway strip under the helicopter skids. The controllers stated that this caused a visual perception of the helicopter being beyond the grass and therefore clear of the runway strip.

Helicopter crew

The helicopter was equipped with a communications system that allowed only the pilot in command to use the radio and consequently, all communications with ATC were performed by the company pilot. However, the flight-test requirements were being specified by the CASA pilot who was the flying pilot for the majority of the tasks. This system therefore required a relaying of requests through both pilots with a resultant increase in workload.

Even though a flight plan had been notified, each test run was slightly different, and the company pilot was unaware of the changes until briefed by the CASA pilot immediately before the run commenced. These briefings included requests from the ground party prior to each run.

During the runway-15 PAPI tests, the crew had made their approaches to the runway centreline and had remained on the runway for most of the time between runs. They had received a landing clearance in each case and that entitled them to remain on the runway until commencing the departure phase of each run. They usually hovered over the grass area when co-ordinating with the ground party. During these manoeuvres, the helicopter hovered both inside and outside the runway strip markers while runway operations continued.

Pilot of the C182

The pilot had received a clearance to make a visual approach and considered it normal to call short final over the threshold and with the speed of the aircraft approximately 130 kts. It was also normal to ask for a long landing in order to minimise taxiing distances to the company dispersal area.

After receiving a clearance to land, he scanned the runway twice but did not see the helicopter. As he was about to touch down, he did see the helicopter and commenced a go-around.

ANALYSIS

Flight planning

Despite agreeing to a date for the flight test a month earlier, the Cairns District Office did not organise the operation until the morning of the test. The CASA pilot just happened to be available at short notice and was not briefed on the requirements until approximately 4-5 hours before the flight.

The verbal pre-brief was not sufficiently adequate for the complexity of the task and did not specify the particular and unusual requirements of the test flight.

The phone facility to ATC was designed for general operations of local flights and not for "one-off" specific tasks of this nature. The complexity of the test was such that it required a specific pre-brief of ATC and a full flight plan, so that all parties were aware of the requirements. The phone plan left the controllers unsure of exactly what was going to happen. This situation resulted in control being based on individual descriptive requests from the helicopter crew as they happened and the belief that the runway was not going to be used after the initial approach.

Aircrew

While both aircrews complied with their respective clearances, each could have been more proactive in putting into place some form of safety net.

The pilot of the C182, by not reporting short final until over the threshold, did not give the ADC time to compensate for any error that may have been made.

The crew of the AS50 heard a landing clearance being given to the C182 but were unsure which runway was being used. They elected not to question the ADC as to the status of the runway.

Aircraft markings

The AS50 helicopter was painted in generally dark colours which made it difficult to see from above, especially above and behind. The lack of contrast between the grey blur effect of rotating rotor blades and the grey of the runway surface gave few visual cues to the pilot of the C182 as he approached to land.

Air traffic control

The controllers believed that the helicopter was operating clear of the runway strip most of the time and considered that the runway-15 PAPI tests were conducted on this basis. While it was unclear how many runs were made to the runway-15 PAPI site, there were in fact, several. However, each one resulted in a landing on the runway centreline and subsequent taxi to the grass areas inside the strip markers. That situation meant that during these runs, ATC were not providing a positive runway separation service between the helicopter and other runway users. However, due to the airborne phase of the test runs involving the centreline, airborne separation was provided at all times. No controller sought clarification of the status of the helicopter following its approach to the runway-33 PAPI site, nor during the previous manoeuvres involving the runway-15 PAPI site.

The belief that the helicopter was operating clear of the runway strip was reinforced by the sighting of grass below the skids and the fact that helicopters rarely use the runways at Cairns. It is normal for helicopters to arrive and depart via a taxiway or helipad and remain clear of the runway at all times.

Because of the late call on final from the pilot of the C182, the ADC had insufficient time to adequately scan the runway for any unexpected obstructions. The fact that he was reading at the time, albeit about the PAPI approach aid, further diminished the amount of time available to perform this duty. It may have also led to a short-term loss of situational awareness.

The supervising ADC had been lulled into a false sense of security by the fact that the familiarising ADC was a rated controller who had been away for only 18 days. He was a bit tired and may have allowed himself to relax more than the circumstances warranted. He had also just left the console momentarily to find the PAPI information, and he thought that this action may have led to some loss of situational awareness.

SIGNIFICANT FACTORS

1. The preparation by the Cairns District Office did not contain an adequate plan for the flight test.

2. The CASA representatives did not adequately brief ATC.

3. Neither ADC maintained an adequate situational awareness.

4. The ADCs did not ensure that the runway was clear prior to issuing a landing clearance; contributing to this situation was the late "short final" call by the pilot of the C182.

SAFETY ACTION

As a result of the investigation:

1. The operator of the AS50 has painted white markings on the rotor blades to improve sighting opportunities from above.

2. The operator of the C182 has issued instructions for pilots to initiate a "final" call at least 300 m prior to the threshold.

3. Airservices Australia has replaced the tower blinds with a better quality product that reduces glare effect.

A Boeing 737 (B737) aircraft was being radar vectored onto final approach to runway 16R at Sydney from a right base, whilst another B737 aircraft was already established on a straight-in approach from 4,000 ft to runway 16L. The aircraft being radar vectored was given an initial instruction to turn right onto 060 degrees and descend to 3,000 ft, followed by a further instruction to turn right onto 130 degrees to intercept the 16R localiser.

However, this instruction was given late, resulting in the aircraft passing through the runway 16R extended centreline at 3,500 ft, conflicting with the leading B737, already established on final to runway 16L. The crew of the following aircraft had the other aircraft in sight at all times. At their closest point, separation was reduced to 1.2 NM laterally and 700 ft vertically. Instructions were then issued to both aircraft to resolve the confliction.

The pilot of VH-CVG contacted Darwin Approach for an Airways Clearance, but due to other traffic in the CTA the clearance was not issued at that time.

A short time later the pilot again contacted approach for a clearance, and the aircraft was then identified at 5,500 ft within the CTA causing a procedural breakdown in separation with the other aircraft. The pilot was not aware that he had entered the CTA steps.

Two foreign military F18 aircraft entered the Darwin CTA without prior warning, or an airways clearance, 57 km south of Darwin and were observed on radar climbing to 9,000 ft.

A Beech Baron aircraft, in the exact same locality, had just been cleared to descend from 8,500 ft to 3,000 ft. A breakdown in separation occurred as the aircraft passed.

The aircrews of the foreign aircraft were rebriefed on Australian ATC procedures and requirements.

FACTUAL INFORMATION

Two international B767 aircraft were tracking northbound on air route B220 at Flight Level (FL) 350, the second approximately 20 minutes behind. All separation in regard to these two aircraft was correctly established and maintained. The aircraft were under the control of Brisbane Sector 10 and were due to cross into the Papua New Guinea flight information region (FIR) at VIPAM, the mandatory reporting position at the FIR boundary. The controller had co-ordinated the pilot estimates for VIPAM with Port Moresby Control.

Subsequently, an A310 aircraft taxied at Port Moresby for a flight to Cairns via air route B220 and the crew had been cleared to climb to FL370 by Port Moresby Control. The Sector 10 controller agreed to this flight level as initial separation responsibility was with Port Moresby Control.

The A310 departed at 1316 EST and was estimating VIPAM at 1341 tracking southbound. As the first B767 was estimating VIPAM northbound at 1346, there was insufficient time to allow an unrestricted climb to FL370 for the A310. The crew were therefore instructed by Port Moresby control to maintain FL330.

During the subsequent co-ordination between Port Moresby control and Sector 10, it was agreed that Sector 10 would accept responsibility for providing separation between all three aircraft and initiating a climb for the A310 when available. During this co-ordination the Port Moresby controller offered the use of Port Moresby distance measuring equipment (DME) to assist Sector 10 in this separation function. The Sector 10 controller was unsure of the process for using such equipment in Australian airspace and decided not to use the DME standard.

Having accepted responsibility for separation, the Sector 10 controller correctly calculated, using mental processes only, a time of passing for the A310 and the leading B767. The estimated time of passing was 1343.30 (transmitted to the aircrews as 1343) and the aircraft sighted each other at that time. However, further climb for the A310 was still dependent on separation being provided with the second B767, which was initially estimating VIPAM at 1416.

While the Sector 10 controller was waiting for confirmation that the first B767 had passed the A310, she commenced the calculation for the time of passing for the A310 with the second B767. The controller's mental calculation was based on a 27-minute time difference derived from the revised VIPAM estimates of the A310 (1341) and the second B767 (1408). The controller calculated this time of passing as 1404 (this was erroneous as the correct time was 1353.30). The required standard was for the climbing aircraft (A310) to reach FL370 by a time 10 minutes before the time of passing. Based on the controller's calculated time of 1404, this requirement would have been 1354. However, because half-minutes are not normally used in these calculations, the controller rounded out on the side of safety and issued an instruction for the crew of the A310 to climb to FL370 with a requirement to reach FL370 by 1353.

At 1347, the crew of the B767 reported their position at DOTOD (a position on air route B220 south of the FIR boundary) and gave an updated estimate for VIPAM that was 2 minutes early. This new estimate had the effect of bringing the time of passing forward by 1 minute and the Sector 10 controller issued a new requirement for the crew of the A310 to reach FL370 by 1352. This requirement was correctly acknowledged.

At 1348, the crew of the A310 reported maintaining FL370. The aircraft passed at 1353. The Sector 10 controller had made a 10-minute error in the time of passing calculation and the separation standard had been breached.

Communication with the three aircraft in the relevant portion of air route B220 was through flight service HF channels. All transmissions and co-ordination procedures in regard to flight service requirements were adequate and in accordance with the appropriate instructions.

The Australian Manual of Air Traffic Services suggests that where separation is based on mathematical calculation, a cross-check of the results should be undertaken. On this occasion, the controller had intended to make such a cross-check using a navigation computer and had prepared the flight progress strip for the northbound B767 in readiness to carry out the second calculation. However, no such check was made. She had only checked her original calculation using the same mental method.

The workload on the Sector 10 controller had been high but most of the traffic separation conflictions had been completed, with co-ordination representing the bulk of the outstanding tasks at the time of the occurrence. However, the sector was still considered to be busier than normal.

ANALYSIS

Examination of the time of passing calculation indicated that using the 27-minute difference and the time of 1341 at VIPAM for the A310 (the point at which the controller based her separation calculation), the calculation should have resulted in a time of passing of 1354.30. This time would have then been rounded out to 1354 and then further amended to 1353 when the crew of the A310 reported at VIPAM at 1339. The difference of 1 minute in this time of passing calculation as compared to the controller's calculation (after subtracting the 10 minutes required by the separation standard and correcting the controller's 10-minute error), could not be adequately explained but was probably a safety net used by the controller when a half-minute was involved in the calculation. Having made the original 10-minute error, the controller made amendments in the single minute column and, because a cross-check was not carried out, the opportunity to remedy the mistake was lost.

The Sector 10 controller knew that a cross-check was required and had intended to carry out such a check for the time of passing involving the second B767. She could not say why this was not done but she was busy and had several items on her mind at the time. One such item was the option to use Port Moresby DME to establish a definite passing. She was unsure of being able to use a foreign navigation aid in Australian airspace and was discussing this option with other controllers.

Having made an error of 10 minutes in the time of passing calculation, certain factors may have reinforced the controller's perception that all was well. Firstly, the time of passing for the A310 and the first B767 had been correctly calculated and had worked as planned. Secondly, the initial estimated times at VIPAM between the A310 and the second B767, indicated that there was enough time for the change of level while maintaining separation standards provided that the crews of the A310 and the preceding B767 saw each other, and that the instruction for the climb was given as soon as those sighting reports were made. This situation would have provided 10 minutes for the crew of the A310 to complete their climb.

Additionally, the controller wanted to provide a good service and give the crew of the A310 the least possible delay for their climb.

However, irrespective of the times involving the A310, there was only a period of 20 minutes between the two northbound aircraft. This period was insufficient for the crew of the A310 to obtain a sighting and positive passing of the first B767, and then to climb to reach FL370 at least 10 minutes prior to passing the second B767.

The position reports that were subsequently made by the three crews indicated that all aircraft reached VIPAM earlier than initial estimates. This situation reduced the time available for the A310 to safely climb when using the controller's incorrect calculations. The aircraft actually passed at 1353.30.

SIGNIFICANT FACTOR

The Sector 10 controller did not carry out a cross-check of the time of passing as suggested by the Australian Manual of Air Traffic Services.

SAFETY ACTION

As a result of the investigation, Airservices Australia issued an instruction to draw the attention of controllers to the common error of carrying the "one" in any 10-minute calculation. They also introduced an additional tool for controller reference in the form of a Time of Passing Graph.

Vertical separation diminished to about 500 feet between two aircraft in controlled airspace. VH-STC was on climb from Essendon, and VH-TWC was ex Geelong and cruising at 6,000 feet.

Initially VH-STJ was cleared to climb to 6,000 feet, but when the departures controller realised that VH-STJ's groundspeed was too slow for it to remain ahead of VH-TWC, he cleared VH-STJ on climb to 5,000 feet and wrote the amended altitude on VH-STJ's flight strip.

To resolve potential conflict with other traffic in the Melbourne area, both VH-STJ and VH-TWC were issued with an amended route clearance, Melbourne - Fenton's Hill - Mangalore. When issuing this amended route clearance, the controller followed the normal practice of including the cleared level. However, he inadvertently cleared VH-STJ to the original flight planned altitude of 6,000 feet instead of the amended altitude of 5,000.

When the controller noticed by radar that VH-STJ continued to climb through 5,000 feet he queried the pilot who discontinued the climb.

Significant Factor

The following factor was considered relevant to the development of the incident:

1. The air traffic controller inadvertently cleared VH-STJ to the wrong altitude.

At 1025 the pilot of VH-NJY contacted Mackay Tower at 30 NM inbound on the 155-degree radial on descent to 6,000 ft. VH-NJY was then cleared to descend to 4,600ft and track via a 5 NM arc to the west of track and then to track overhead for a NDB approach. At 1027, VH-EWS departed Mackay for Brisbane tracking on the 137-degree radial on climb to 10,000 ft. Mackay tower controllers commenced trying to visually observe VH-NJY inbound. This was done by the use of standard issue binoculars. The inbound track of the aircraft is situated over a prominent topographical feature known by tower staff, however, VH-NJY could not be visually acquired at this stage. At 1029, VH-NJY was observed visually at approximately 12 NM and 12-13 degrees east of track. VH-EWS was 6 NM on the 137-degree radial. VH-NJY was instructed to turn left to commence the diversion for the NDB approach.

A traffic alert was not issued to the aircraft, as it was the judgement of both controllers on duty that although the aircraft were found to be closer than normal, a collision risk did not exist. They believed there was approximately a mile laterally between both aircraft, and they were diverging. Subsequent replay of the radar tape indicated that VH-NJY and VH-EWS passed each other within approximately 0.7 NM laterally and 800 ft vertically. The Aeronautical Information Publication Australia (AIP) Air Traffic Rules and Services (RAC) 44.4.3 requires aircraft to be navigated by reference to the aid which provides the most precise track guidance, which in Mackay is the Mackay VHF Omni Range (VOR). The pilot in command is required at all times to take positive action to regain track as soon as a deviation from the correct track is recognised. The VOR tracking tolerance at 10 NM is approximately plus or minus 0.9 NM VH-NJY indicated on radar as being approximately 2.6 NM off track at 10 NM which is 1.7 NM outside the approved tolerances. Had this fact been known to air traffic controllers, then corrective action to ensure separation could have been taken. Mackay tower is not equipped with radar. Radar data from Swampy Ridge radar sensor is processed through the technical facilities at Mackay, enroute to Brisbane centre, but no radar display is provided for tower controllers. VH-NJY was under radar control during the flight until the aircraft was transferred to Mackay tower at 30 NM when radar services were terminated. The separation technique being used by tower controllers was one of visually monitoring the outbound aircraft on a track that was plotted on a map to be clear of the procedural tolerance, (in this case 5.2 degrees off the VOR radial, plus an additional 1 NM lateral separation buffer), of the inbound aircraft. No documentary evidence could be found to permit the application of this standard.

The pilot in command (PIC) of VH-NJY was a check captain and the copilot (CP), a first officer, was undergoing command training. The PIC had requested an NDB approach as a training exercise and had selected the VOR selectors off to simulate their failure. He was aware of VH-EWS departing on the 137 radial and tracking to Gladstone. At 10 NM he noted that the trainee had allowed the aircraft to diverge to the right of the 155 radial. The PIC did not bring this to the attention of the trainee, in order to see if he was going to fly outside tracking tolerances. The PIC said that at no time did the ADF needles indicate the aircraft was any further east than the 150 radial. He was satisfied that the aircraft was well clear of the Hay Point helicopter pad which is located near the 137 radial. He also had VH-EWS in sight passing to the right and was satisfied he was well clear. In summary, the PIC of VH-NJY was operating outside tracking tolerances and outside the terms of his airways clearance. This was due to deselection of the most accurate navigation aid (the Mackay VOR) to simulate its failure for training purposes. A non documented separation standard was used by the tower controllers. An instruction has been issued to all Northern District Towers that until a separation standard is developed and approved, outstation staff are to apply only those separation standards that are included in the Manual of Air Traffic Services (MATS).

The radar sector providing enroute control to VH-NJY did not advise the pilot that radar services were terminated when he was handed off to Mackay tower. The District Safety and Quality Management Branch has recommended that radar controllers advise pilots proceeding into procedural tower environments within radar coverage, when radar services are terminated. Weather conditions were fine, with Mackay under the influence of a high-pressure system, QNH 1023, nil cloud, visibility in excess of 10 km, and a light south-easterly wind.

FACTUAL INFORMATION

A British Aerospace 146 (BA146) had departed Brisbane for Proserpine on climb to FL260. Four minutes later a Boeing 747-Special Performance (B747SP) departed Brisbane en route to Taipei on climb to FL350. The initial departure track was the same for both aircraft and was to the northwest of Brisbane. The Brisbane Sector 3B controller believed from past experience, that the rate of climb of the B747SP would far exceed that of the BA146. Consequently, he decided to monitor the horizontal separation on the radar display until vertical separation was achieved.

Approximately ten minutes after departure, the crew of the B747SP observed on the aircraft collision avoidance system (ACAS) display an aircraft ahead and at the same level. From the high rate of closure, the crew estimated that there would be a breakdown in separation very shortly unless action was taken to avoid the aircraft. They requested the Sector 3B controller advise them of the traffic. At the time, the horizontal separation between the aircraft was just over 5 NM and the groundspeed of the B747SP was 100 kts faster than that of the BA146.

The Sector 3B controller had been operating the position for the previous two and a half hours. He had been busy, but the number of aircraft had reduced in the last 15 minutes. During the last 30 minutes he had answered a number of radio calls from the pilot of a Visual Flight Rules (VFR) flight which was operating outside controlled airspace but in his area of responsibility for a radar advisory service (RAS). RAS had been introduced one month previously, and the sector had almost full radar coverage in non-controlled airspace. Consequently, the sector controllers often had pilots operating on the frequency using RAS procedures. The pilot of the VFR aircraft was incorrectly pre-fixing his radio transmissions with "Brisbane Centre" which required an acknowledgement from the Sector 3B controller. This had been annoying and was frustrating the controller. He had felt relieved when the pilot of the VFR aircraft transferred to an adjacent control position; Sector 3L.

When the crew of the B747SP transmitted to the controller requesting advice of the traffic ahead, the Sector 3B controller had been discussing aspects of the VFR flight with the Sector 3L controller. The Sector 3L controller was providing a RAS in his sector and had queried the Sector 3B controller with respect to the previous transmissions from the pilot of the VFR aircraft. The controllers had not utilised the intercom communications system to discuss the flight but had talked between the two consoles. Consequently, the Sector 3B controller's attention was diverted from his display as the horizontal separation between the B747SP and BA146 approached the minimum required.

After returning his attention to the display, the controller observed that the 5 NM radar separation standard was about to be infringed as the B747SP approached the BA146. The crew of the BA146 were unaware that the B747SP was approaching their aircraft from behind. The Sector 3B controller immediately instructed the crew of the B747SP to turn right in an endeavour to maintain separation between the two aircraft and then advised the crew that the traffic was a BA146. The crew of the B747SP complied with the Sector controller's instructions. The Sector 3B controller instructed the crew of the BA146 to maintain FL230 and then requested the crew of the B747SP to expedite climb until passing FL240. The horizontal separation reduced to 2.7 NM before vertical separation of 1,000 ft was established. There was a breakdown of separation.

ANALYSIS

The Sector 3B controller was relying on maintaining horizontal separation until vertical separation was achieved. The maintenance of adequate horizontal separation was conditional upon the regular scanning of the radar display by the controller. This was especially so because of the significant overtaking groundspeed of the B747SP.

Once the controller elected to monitor the situation instead of using a method of separation assurance, he needed to concentrate more on the radar display. However, he allowed himself to be distracted, firstly by the radio transmissions from the pilot of the VFR aircraft and secondly, by conversing with the adjacent sector controller. His concentration may also have lapsed to some degree because of the reduction in the number of aircraft on frequency in the previous 15 minutes.

Had the aircraft not been fitted with an ACAS, or had the crew not queried the controller, there was the possibility of a collision. Without an ACAS the crew may have observed the BA146 through the aircraft's windscreen; however, this would have been subject to the crew's cockpit workload. Their attention may have been inside the aircraft and consequently they would not have seen the BA146. The operation of the ACAS in the B747SP and the crew's request for traffic information to the controller were active defences in the situation.

SIGNIFICANT FACTORS

1. The Sector 3B controller did not utilise separation assurance techniques.
2. The Sector 3B controller's attention was diverted from monitoring the radar display during a critical phase.
3. The B747SP crew's use of the ACAS and subsequent request for traffic information alerted the controller to the possibility of a breakdown in separation.

A military Hercules (C130) aircraft had departed Richmond, NSW for Canberra, ACT and was initially assigned climb to 6,000 ft by Departures South control (DepS). The intention of the controller was to climb the C130 to be at a level above that required for arriving aircraft to have vacated on descent, by the crossing point of the tracks. Such a climb would have required the C130 to reach 9,000 ft before the respective tracks came into conflict.

A Boeing 747 (B747) was inbound to Sydney, NSW on a flight from Melbourne, Vic. and had been assigned descent to 6,000 ft, via an appropriate standard arrival route, by Approach South control (AppS).

As the two controllers radar vectored their respective aircraft, the Departures North controller (DepN) observed that the aircraft were coming into conflict and alerted both the AppS and DepS controllers. Radar vectors and traffic information were given to the crews of both aircraft, and they passed within 2 NM of each other at the same height. The separation standard is 3 NM in this situation and, therefore, a breakdown of separation occurred.

Sydney airspace is divided into various areas of jurisdiction, and, in this case, AppS had descended the B747 in accordance with this airspace management agreement. However, the controller did not notice that the C130 was at an inappropriate altitude and in his area of responsibility.

The DepS controller had a choice of methods that he could use to separate the C130 from arriving traffic. He could have instructed the C130 to maintain 5,000 ft, i.e. 1,000 ft beneath the allocated arrival altitude, or, as he chose in this case, he could have directed the C130 to climb to an altitude above that required by the arrival procedure.

The workload and complexity of the traffic situation for the DepS controller was high, and although his plan of action was sound, he forgot to instruct the C130 to climb.

SIGNIFICANT FACTORS

1. The workload and complexity of the task of the DepS controller were high.
2. The DepS controller forgot to take the action which would have guaranteed the separation between the B747 and the C130.
3. The AppS controller did not notice that the C130 was at an inappropriate altitude for its track.