Separation issue

Throughout this analysis it should be noted that the pilots of both aircraft and the ATS controller involved in the occurrence complied with the rules and procedures for operation in Class E airspace associated with the NAS phase 2b, implemented on 27 November 2003.

The regulations, procedures and educational material associated with that implementation stated that there was a shared responsibility by pilots of IFR and VFR flights to see-and-avoid each other in Class E airspace.

Prior to the implementation of NAS phase 2b on 27 November 2003, both aircraft involved in this occurrence would have been operating in Class C airspace. As such, they would have been subject to an ATS airways clearance and would have been provided with separation in accordance with Class C airspace rules and procedures. In order for two aircraft to pass in close proximity at these flight levels in Class C airspace, those rules and procedures would need to have been compromised. As the pilots of both aircraft and the ATS controller complied with the rules and procedures for Class E airspace under NAS, those rules and procedures do not preclude an IFR high performance, high-capacity regular public transport aircraft from passing within such close proximity as to generate a TCAS RA on either known or unknown VFR traffic.

The controller's relatively low workload and other factors, such as the Lancair pilot submitting flight notification details, and broadcasting his departure from Maroochydore, assisted the ATS controller to detect a possible conflict. Although there was no requirement for the controller to pass traffic information to the pilot of the Lancair about the location of the 737 under NAS Class E airspace procedures, the controller provided traffic information to both aircraft with respect to each other.

Part 5 of MATS also stated that controllers shall issue a safety alert when, in the consideration of the controller, such an advice was warranted to avoid conflict. In the circumstances of this occurrence, the controller had provided traffic information to the crews of both aircraft, and the Lancair pilot had broadcast that he had the 737 in sight. Accordingly, the onus was then on the Lancair pilot to avoid the 737. In those circumstances, the provision of a safety alert, which may have included a suggested course of action, may also have complicated the situation, if that suggestion was contrary to what the pilots of each aircraft considered necessary.

Provision of a safety alert, in the circumstances of this occurrence, was not required. However, MATS did not provide any guidance to controllers on the circumstances under which the provision of a safety alert would be appropriate. Publication of those guidelines may assist controllers to determine when a safety alert should be issued.

In Class E airspace, the provisions of CAR 163A required the crews of both aircraft to 'see and avoid' each other. The 737 crew were unable to see the Lancair despite their attempts to do so. The Lancair pilot reported that he had the 737 in sight. When the 737 crew observed the position of the Lancair on the TCAS navigation display, they commenced action to avoid a confliction prior to receipt of both the TCAS TA and RA. In concert with that action, they continued in their attempts to visually acquire the Lancair, in accordance with Class E airspace see-and-avoid requirements.

In the circumstances of this occurrence:

• the ATS controller took more actions than those required by the published requirements for Class E airspace and MATS;
• the Lancair pilot took more actions than those required by the published procedures for Class E airspace under NAS;
• the early action taken by the 737 crew to avoid the conflict was not contrary to the published procedures for Class E airspace under NAS.

Despite those actions, the two aircraft came into such proximity that a TCAS RA was generated in the 737.

Both aircraft were operating in Class E airspace that was introduced as part of the National Airspace System (NAS) phase 2b on 27 November 2003. (An ATSB research report titled National Airspace System Stage 2b: Analysis of Available Data was released in July 2004.) As no prescribed separation standards are applicable in these circumstances, there was no infringement of separation standards. However, ATS audio tapes, radar and TCAS data, and information obtained from the air traffic controller and the pilots of both aircraft were consistent and indicate that the aircraft came into such close proximity that a threat to the safety of the aircraft may have existed. Therefore, the incident has been classified by the ATSB as an airprox event.

The incident at Canty IFR reporting point, on 3 December 2003 (ATSB report 200304963) was also classified as an airprox event.

Unlike this incident north of Brisbane on 7 April 2004 and the Canty incident, the occurrence near Launceston on 24 December 2003 (ATSB report 200305235) was classified as a serious incident due to the lack of radar coverage in the Launceston area and the absence of radio broadcasts from the pilot of the Tobago, which created an unalerted see-and-avoid environment for the crew of the Boeing 737. The air traffic controller also was unaware of the Tobago.

On 7 April 2004, a Boeing 737-7BX (737) aircraft registered VH-VBT, operating under the instrument flight rules (IFR), was en route from Townsville and descending for a landing at Brisbane. A Neico Lancair IV-P aircraft registered VH-LDJ, operating under the visual flight rules (VFR), was en route from Maroochydore to St George, on climb to flight level (FL) 165¹. Both aircraft were operating in radar Class E airspace at the time of the occurrence.

The Lancair pilot reported to the Air Traffic Services (ATS) controller that he had departed Maroochydore at 0718 Eastern Standard Time², although in accordance with the National Airspace System (NAS) procedures, there was no requirement for him to do so³. The controller issued the Lancair pilot with a discrete transponder code to assist with his situational awareness. Published NAS procedures stated that:

In Class E airspace, IFR and VFR flights are permitted. IFR flights are provided with an air traffic control service, are separated from other IFR flights, and receive traffic information on VFR flights as far as is practicable. VFR flights receive a Radar Information Service (RIS)⁴ on request.⁵

Those procedures also stated that, for VFR aircraft operating in Class E airspace, '…no flight notification was required…' and pilots of aircraft conducting operations under the VFR were required to monitor the appropriate radio frequency. The Lancair pilot submitted flight notification details to ATS prior to departure from Maroochydore, and reported that departure to ATS.

In accordance with those procedures, the controller was not providing traffic separation⁶ to either aircraft, and advised the 737 crew accordingly. Recorded ATS audio information showed that the controller provided traffic information about the Lancair to the 737 crew on three occasions between 0721:58 and 0725:08. At 0722:17, and again at 0725:38, the controller provided the Lancair pilot with traffic information about the 737, although there was no requirement for him to do so in Class E airspace. During the first transmission at 0722:17, the controller advised the Lancair pilot that the 737 was crossing traffic which would pass in about 15 NM and was on descent into Brisbane. During the second transmission at 0725:38, the controller advised the Lancair pilot that the 737 was 'in your 2 o'clock at 8 miles now'. ATS radar data showed that, at 0725:38, the 737 was 8.8 NM from the Lancair. At 0725:47, in response to that broadcast, the Lancair pilot advised the controller that he had the 737 in sight.

As the 737 was passing through about FL157 at 0726:01, the crew reported that they observed a traffic alert and collision avoidance system (TCAS)⁷ traffic symbol on the aircraft's navigation display, about the Lancair. They attempted to visually acquire the Lancair, but were unable to see that aircraft. Recorded data from the 737's flight data recorder (FDR) showed that, at that point, the crew commenced manoeuvring the aircraft by reducing the rate of descent. At about 0726:18, the crew received a TCAS traffic advisory (TA)⁸. The crew reported that they were still unable to visually acquire the Lancair and were uncertain of its relative position. Recorded FDR data indicated that at 0726:34, the crew disengaged the autopilot and commenced a right turn away from the Lancair. They subsequently levelled the 737 at FL153 and then climbed to FL154. At 0726:40 and at 15,420 ft the 737 received a TCAS resolution advisory (RA)⁹ aural warning instructing them to climb, in response to the proximity of the Lancair. They subsequently climbed the 737 to FL166 and continued the turn to about 15 degrees right of track. The duration of the RA was 10 seconds and commenced when the Lancair was about 650 ft vertically lower and about 0.7 NM to the left of the 737.¹⁰ Recorded ATS radar data showed that, at about 0726:45, the Lancair altered track 8 degrees to the right away from the 737, just before passing behind and below the 737. The Lancair pilot reported that he did not experience the effect of wake turbulence from the 737. The minimum distance between the two aircraft was about 600 ft vertically at about 0.3 NM laterally.¹¹

The Class E airspace in which the 737 and the Lancair were operating at the time of the occurrence was introduced as part of NAS phase 2b on 27 November 2003. Prior to NAS phase 2b, that volume of airspace was classified as Class C airspace. In Class C airspace, both aircraft would have been subject to an ATS airways clearance and would have been separated in accordance with prescribed standards.

In Class E airspace, the pilots of aircraft operating under the IFR and VFR were required to:

…maintain vigilance so as to see, and avoid other aircraft.¹²

The NAS Implementation Group reference guide, distributed as part of the NAS phase 2b implementation, stated that:

The other important change is that the pilot of a VFR flight should not make broadcasts on ATC frequencies.¹³

It also stated that:

Pilots of VFR flights may monitor the ATC frequency to enhance situational awareness.

Please do not make broadcast transmissions or engage in chatter on an ATC frequency. The safety of others depends on you not doing this.

Pilots are not precluded from responding to any ATC or pilot transmission when they believe their safety is at risk from another aircraft.

Part 2, Section 2, paragraph 2.2.4.1 of the Manual of Air Traffic Services (MATS) stated that:

Before providing a radar service to an aircraft, radar identification shall be established.

Although the controller did not advise the Lancair pilot that the Lancair was radar identified, the controller issued a discrete transponder code to the Lancair pilot and radar-identified the aircraft before providing a Radar Information Service to the pilot.

Part 4, Section 1, paragraph 4.1.1.1 of MATS contained information regarding ATS controller responsibilities for providing aircraft separation. The manual stated that:

Separation shall be provided by ATC using approved separation standards and procedures.

In the circumstances of this occurrence, the ATS controller was not required to provide separation to either aircraft in respect of the other and there were no separation standards applicable in these circumstances in Class E airspace.

Part 4, Section 1, paragraph 4.1.1.3 of MATS stated that:

Nothing in this chapter precludes a controller from using discretion and initiative in any particular circumstance where these procedures appear to be in conflict with the requirement to promote the safe conduct of flight.

In the circumstances of this occurrence, the ATS controller provided traffic information to the crews of both aircraft in respect of the other, although under NAS procedures there was no requirement for him to provide traffic information to the pilot of the Lancair on the location of the 737.

Part 5, Section 1, paragraph 5.1.13 of MATS provided information regarding provision of safety alerts. Paragraph 5.1.13.1 stated that:

A safety alert shall be issued to an aircraft when a controller is aware the aircraft is in a situation which is considered to place it in unsafe proximity to terrain, obstructions, or other aircraft.

The controller reported that, once the Lancair pilot broadcast that he had the 737 in sight, there was no necessity to broadcast a safety alert to either the Lancair pilot or the 737 crew. The controller also reported that if that pilot had not broadcast that he had the 737 in sight, his next option was to issue a safety alert. MATS did not provide any guidance to controllers on what might be considered '…unsafe proximity…', or when to issue a safety alert.

The NAS Implementation Group reference guide contained information for VFR pilots regarding separation from other aircraft when operating in Class E airspace. Page 16 of that guide stated that:

When you are flying in Class E airspace you are responsible for separation from other aircraft. The onus is on you to look out and see and avoid other aircraft.

Part 12, The Rules of the Air, Division 1, of the Civil Aviation Regulations (CAR) 1988, contained information regarding right of way, prevention of collision, operating near other aircraft and responsibilities of flight crew to see and avoid aircraft. More specifically, CAR 161 contained information regarding right of way and stated that:

(1) An aircraft that is required by the rules in this Division to keep out of the way of another aircraft shall avoid passing over or under the other, or crossing ahead of it, unless passing well clear.¹⁴

(2) The pilot in command of an aircraft that has the right of way must maintain its heading and speed, but nothing in the rules in this Division shall relieve the pilot in command of an aircraft from the responsibility of taking such action as will best avert collision.

CAR 162 (1) contained information regarding prevention of collision and stated that:

When 2 aircraft are on converging headings at approximately the same height, the aircraft that has the other on its right shall give way…

Although not specifically referring to converging aircraft, CAR 162 also stated that '…each shall alter its heading to the right…', and when referring to the aircraft other than the aircraft having right of way, '…shall keep out of the way of the other aircraft by altering its heading to the right…'.

CAR 163 (1) contained information regarding operating near other aircraft and stated that:

The pilot in command of an aircraft must not fly the aircraft so close to another aircraft as to create a collision hazard.

The 737 was on the Lancair's right and, in accordance with CAR 161 and CAR 162 (1), had right of way. The Lancair pilot reported that he had the 737 in sight. While the crew of the 737 had observed a traffic symbol on the TCAS display, they reported that they did not see the Lancair, despite attempts to do so.

Information obtained from the crews of both aircraft, the ATS controller, recorded flight data from the 737, ATS audio recordings and radar data, was consistent and indicated that the crews of both aircraft and the ATS controller complied with the published procedures for Class E airspace under NAS.

Based on the factual data, and the definition contained in Regulation 2.2 of the Transport Safety Investigation Regulations 2003, the incident was classified as an airprox event.¹⁵

¹ 16,500 ft with an altimeter pressure sub-scale setting (QNH) of 1013.2 hPa.
² The 24-hour clock is used in this report to describe the local time of day, Eastern Standard Time (EST), as particular events occurred. Eastern Standard Time was Coordinated Universal Time (UTC) + 10 hours.
³ Aeronautical Information Publication (AIP), ENR 1.1, Sections 3.4 and 18.3.2.
⁴ Radar Information Service (RIS) is defined in Part 10, Section 1 of the Manual of Air Traffic Services as:

An add-on ATC service within radar coverage, which provides information to flights, not otherwise receiving a separation service, in order to improve situational awareness, and assist pilots in avoiding collisions with other aircraft.

⁵ AIP, ENR 1.4, Section 2.1.4 and pages 12-13 and 40 of the NAS Implementation Group Reference Guide - How to Operate in the National Airspace System, effective from 27 Nov 2003.
⁶ Separation is defined in Part 10, Section 1 of the Manual of Air Traffic Services as:

A controlled condition using defined standards to prevent collisions between aircraft.

⁷ The Boeing 737-NG Operations Manual, Volume 2, states that:
 

TCAS alerts the crew to possible conflicting traffic. TCAS interrogates operating transponders in other airplanes, tracks the other airplanes by analysing the transponder replies, and predicts the flight paths and positions. TCAS provides advisory, flight path guidance, and traffic displays of the other airplanes to the flight crew. Neither advisory, guidance, nor traffic display is provided for other airplanes which do not have operating transponders. TCAS operation is independent of ground-based air traffic control.

⁸ A traffic advisory (TA) is generated when the other aircraft is approximately 40 seconds from the point of closest approach, dependent upon aircraft altitude.
⁹ If the other aircraft continues to close, a resolution advisory (RA) is generated when the other aircraft is approximately 25 seconds from the point of closest approach, dependent upon aircraft altitude. The RA provides aural warning and guidance as well as manoeuvre guidance to maintain or increase separation from the traffic.
¹⁰ The recorded ATS radar data and the 737 flight recorder data was consistent. However, the accuracy of that information is dependent upon the tolerances associated with both aircraft altimeters and the ATS radar equipment.
¹¹ The horizontal distance was determined using the radar positions that were recorded every 5 seconds. By interpolating between those points to derive a position every second, the minimum horizontal separation was 0.3 NM, dependent upon the tolerances previously mentioned.
¹² Civil Aviation Regulations 1988, 163A - Responsibility of flight crew to see and avoid aircraft.
¹³ Page 8 of the NAS Implementation Group Reference Guide - How to Operate in the National Airspace System, effective from 27 Nov 2003.
¹⁴ The investigation was unable to locate a CAR definition of '…well clear…'.
¹⁵ An airprox event is defined in Regulation 2.2 of the Transport Safety Investigation Regulations 2003, as:

…an occurrence in which 2 or more aircraft come into such close proximity that a threat to the safety of the aircraft exists or may exist, in airspace where the aircraft are not subject to an air traffic separation standard or where separation is a pilot responsibility.

1. The flight crew and air traffic control staff did not brief effectively before the calibration flight.
2. The Astra crew was unaware that Brisbane Centre was responsible for management of a portion of R577.
3. The Astra crew was unable to maintain continuous two-way communications with flight service international.
4. The provision of radar coverage and use of secondary surveillance radar transponders in oceanic airspace assisted in the resolution of the conflict.

The briefing planned between the Astra crew and Williamtown Air Traffic Control staff did not occur and as a result, the air traffic control staff were not fully conversant with the Astra crew's intentions. Also, the Astra crew were unaware of the unique delineation in airspace management responsibilities for the area where they intended to operate. These aspects made it difficult for the crew to adequately prepare for contingencies and for air traffic controllers to understand the complex nature of the calibration task.

The Astra crew complied with the clearance issued by Williamtown Air Traffic Control. However, the clearance was issued without air traffic control being fully conversant with the flight profile. The misunderstanding was compounded by the Astra crew believing that their flight would be managed by Williamtown Air Traffic Control. If the crew had been aware of the ramifications of the Jordy Release, it was likely that they would have appreciated that the initial stages of the flight would pass back and forth between R577 and non-controlled airspace. Had they been aware of this fact and that consequently, they were responsible for their own traffic avoidance, the Astra crew may have ensured that air traffic services were advised of the intention to change level well in advance of commencing the climb to FL200. If the crew had been able notify flight service international of their intention to climb from 10,000 ft to FL200 it was probable that they would have been issued with traffic information on the Dash 8 and the conflict may not have occurred.

The operation of the Astra's transponder on the assigned code assisted in the resolution of the situation. An alternative for the crew was to select the transponder to the radio failure code of 7600, which was part of the aviation safety net. Given the complex nature of the task and the communication difficulties being experienced by them at the time, this action may have provided a more timely alert to air traffic agencies. Had air traffic agencies been alerted by the change in code to 7600, it is likely that air traffic control or flight service international officers would have either provided traffic information or initiated action to separate other aircraft in the vicinity of the Astra.

The Brisbane Ocean sector controller saw on radar an unidentified aircraft climbing through flight level (FL)180. The controller issued traffic information to the crew of a Dash 8 operating an instrument flight rules (IFR) flight from Lord Howe Island to Sydney at FL200. The crew of the Dash 8 sighted the unidentified aircraft at an approximate distance of 5 NM and 1,500 ft below them. The two aircraft passed with 3 NM lateral separation at the same level. The unidentified aircraft was subsequently identified as an Astra conducting an IFR calibration flight. It appeared that the crew of the Astra had not complied with Aeronautical Information Publication (AIP) procedures for changing levels in non-controlled airspace. These procedures require pilots of IFR category aircraft operating in non-controlled airspace to notify the relevant air traffic agencies of any changes in altitude/level. Investigation of the occurrence revealed that the Astra crew were not notified of a change in airspace management for their area of operations.

The Astra crew was conducting a calibration of a new radar that had been installed at Williamtown aerodrome. This required the aircraft to track outbound from Williamtown at 1,500 ft, in a direction clear of local operating areas and air routes, until radar coverage was lost and then return on the reciprocal track while climbing. Once the next altitude or level was reached the crew would immediately turn the aircraft to track outbound again. The manoeuvre was to be repeated at 10,000 ft, FL200, FL300 and FL400 and would conclude with the aircraft completing the task at approximately 220 NM from Williamtown.

The Astra crew had prepared and dispatched written briefs on the task to Williamtown and Brisbane Air Traffic Control (ATC) agencies. However, the calibration task schedule was amended and subsequently conducted 24 hours earlier than originally notified. The brief depicted the calibration flight as being a series of steps with an increase in altitude/level as the distance from Williamtown increased but did not depict that the aircraft would fly the reciprocal track at any stage. After the Astra had departed Williamtown to commence the calibration, the Williamtown approach coordinator briefed the Brisbane Flight Service International officer on the task, based on the briefing and other details as subsequently advised by the crew.

The general practice of the Astra crew was to conduct personal briefings with the responsible air traffic control staff on the day of a calibration task and this was their intention on the day of the occurrence. However, when the Astra arrived at Williamtown, the senior air traffic control officer who had planned to attend the briefing was not available. Consequently, the crew only briefed a technical ground party.

The Astra crew was issued a clearance by Williamtown Air Traffic Control to track via the 100 tactical air navigation aid radial on climb to FL210. On this track the Astra would transit Williamtown restricted area R577 which was promulgated as continuously active, 24 hours a day. The intended track of the Astra entered and exited R577 respectively at 25 NM and 130 NM east of Williamtown. The vertical limits for the area are from sea level to FL600. When not required for military operations a notice to airman (NOTAM) deactivating R577 for specific periods was normally issued by Williamtown Air Traffic Control. A deactivation NOTAM was not issued for the period of the calibration flight.

As an aid to airspace management, Brisbane and Williamtown Air Traffic Control agencies had agreed to automatically release portions of R577 and other restricted areas to Brisbane when the restricted areas were active. This agreement was published in the Northern New South Wales Manual of Air Traffic Services Supplement (MATS SUPP) which in turn was part of both Williamtown and Brisbane operating procedures. The agreement effectively transferred airspace management responsibility for the south-east portion of R577, known as the Jordy Release, from Williamtown Air Traffic Control to Brisbane Centre. The planned track of the Dash 8 passed through the Jordy Release.

The lateral and vertical limits for Australian airspace were published in the Airservices Australia Designated Airspace Handbook (DAH) and depicted on AIP charts. The DAH, charts or a NOTAM can be used for flight crew pre-flight briefing. None of the documents included the MATS SUPP provisions.

A letter of agreement between Brisbane Ocean sector, Brisbane Flight Service International and Sydney Flight Service 4 detailed the airspace management responsibilities for the Jordy Release when transferred to Brisbane Centre. The division of responsibilities was:

• Ocean sector
  That portion of the release above FL200 between 90 NM and 150 NM from Sydney and above FL245 outside of 150 NM Sydney,
• Flight Service International
  That portion of the release at FL200 and below that level outside of 90 NM from Sydney, and
• Sydney Flight Service 4
  That portion of the release below the control area steps inside 90 NM from Sydney.

The Ocean sector controller was required to separate IFR aircraft as if they were in controlled airspace. The officers of both flight service units were required to issue traffic information to pilots of IFR category flights, just as they would have for pilots of IFR flights in non-controlled airspace, in accordance with the Manual of Air Traffic Services (MATS) criteria. Part of the MATS criteria required traffic information to be issued when aircraft were climbing or descending through the level of another aircraft when these aircraft were within 15 NM or 10 minutes longitudinally or laterally. Ocean sector uses radar and procedural control methods to separate aircraft. Radar coverage extends to beyond the eastern limit of R577. Neither of the flight service units had access to radar services.

Because of the flexible airspace management arrangements for the Jordy Release, flight service international officers usually pre-empted requests for confirmation of the availability of planned routes for aircraft inbound to Sydney. Normal practice was to advise crews as early as possible when the area was active with military operations to enable them to commence tracking via alternative routes. The crew of the Dash 8 was not advised that their planned route was unavailable. The crew was subsequently advised to contact the Ocean controller at 140 NM from Sydney for a clearance.

The Astra crew reported that due to R577 being active, they believed that, their flight would be managed by Williamtown air traffic control. The Williamtown coordinator advised flight service international that the crew had been cleared to FL210 but that initially they would maintain 1,500 ft. The coordinator subsequently advised flight service international that the Astra had climbed to 10,000 ft. The Astra crew was instructed that they were leaving the Williamtown restricted area and to transfer to flight service international on high frequency (HF) radio. This was required as they were operating in that portion of R577 being managed by flight service international.

After several attempts, the Astra crew contacted flight service international on HF radio and was advised of another HF frequency to use if they were having communication difficulties. There was no further contact with the crew on HF radio. The flight service international officer attempted unsuccessfully to contact the crew. The problems with the HF radio communication were believed to be the result of propagation difficulties. Once it was apparent to the crew that HF communication was not viable they tried to establish communications with Brisbane Centre via VHF. The crew reported after the occurrence that because they were unable to advise any air traffic service agency of the next climb, from 10,000 ft to FL200, they broadcasted their intention on the VHF emergency frequency, 121.5 MHz. The investigation could not establish whether other crews heard the transmission.

The crew contacted the Nambucca Sector Controller and reported that their position was 120 NM east of Williamtown on the 100 radial and that the aircraft had left 10,000 ft on climb to FL200. The Nambucca controller confirmed that the Astra was tracking west and that at 110 NM from Williamtown the crew would commence a turn to track outbound. The Nambucca controller contacted the Ocean controller to report the Astra's position. At approximately the same time the Ocean controller was issuing a clearance to the crew of EA261 and shortly after noticed an unidentified aircraft approaching the Dash 8. The Nambucca controller issued traffic information to the crew of the Astra, who arrested the climb of their aircraft and then descended to FL185.

The Astra crew did not select the radio failure code of the aircraft's secondary surveillance radar transponder. The investigation did not establish why the crew did not change the transponder code.

FNB should have been reported as potential traffic to the crew of FNA since its track was planned to be within 15 NM laterally of FNA's route and because it was climbing through FNA's level.

The flight service officer reported that he would have normally passed traffic information to the pilots when FNB taxied at Carnarvon. However, on this occasion, he did not recognise that the two aircraft were potentially conflicting traffic. Having calculated a release time of 0225 when he expected FNB to be above FL200, in controlled airspace and therefore clear of FNA, he may have assumed that the traffic had no potential for conflict. An indication of his assumption was that he filed the flight strip for FNB soon after the release time; therefore, the potential for conflict of these two aircraft was never recognised by the flight service officer.

The flight service officer did not have a history of inadequately passing appropriate traffic information although he had, on occasion, used inappropriate air traffic control procedures.

The incident probably occurred as a result of a combination of factors. Firstly, the flight service officer reported that he was pre-occupied with his personal situation and was tired. As a result, he probably did not adequately monitor the progress of his routine actions. Secondly, he reported that he might have used a presumed rate of climb for the Fokker 50 as a basis for determining whether the traffic was potentially conflicting. Such a calculation was erroneous and irrelevant because the traffic assessment criteria in the Manual of Air Traffic Services required the traffic information to be passed. The use of this calculation may have been a manifestation of the flight service officer's occasional use of inappropriate procedures. His pre-occupation, tiredness and deviation from standard operating procedures may have contributed to the flight service officer losing situational awareness and as a result, he did not recognise that the flight paths of FNB and FNA were potentially conflicting.

Once the flight service officer had committed to not advising the crews of FNB and FNA of each other's presence, there were no organisational defences available, such as active supervision, to preclude the mistake going unnoticed. As a result, once the flight service officer had made the error, there was no backup.

Because the pilot in command of FNB did not need to take any avoiding action, it is unlikely that the provision of TCAS stopped an accident from occurring. However, the fact that TCAS had alerted the crew of FNB to the close proximity of traffic unknown to them indicated that it would have been the only defence available had the two aircraft been on a collision course. The effectiveness of TCAS in alerting and directing the crew of FNB to proximal traffic also illustrated the weakness of the principle of see-and-avoid.

CONCLUSION

The flight service officer was fatigued and distracted, probably as a result of stress and inadequate rest before commencing his shift. Consequently, he did not adequately monitor the progress of his routine actions and he did not notice that the two aircraft were potentially conflicting traffic. He did not provide traffic information to the pilots of the two aircraft as required by Manual of Air Traffic Services.

Sequence of events

At 0208 coordinated universal time (UTC) VH-FNB, a Fokker 50, departed Carnarvon for Perth southbound via air route B469 and was climbing to FL210. The two-way air route was a direct track between Carnarvon and Geraldton . VH-FNA, also a Fokker 50, had departed Geraldton for Learmonth and was tracking via the B469 northbound. The crew of FNA had reported to Perth Flight Service at 0201 that the aircraft was on descent to FL180 from FL200. At 0213, they reported at position HAMEL and were estimating overhead Carnarvon at 0246. HAMEL was a reporting point located 120 NM south-south-east of Carnarvon. FNB's estimated time of arrival at HAMEL was 0242.

About 65 NM south-south-east of Carnarvon and approaching FL180, the co-pilot of FNB glanced down at the traffic alert and collision avoidance system (TCAS) display and noticed a return in the 11-o'clock position at about 7 NM at the same level. The pilot in command of FNB, aware that FNA was likely to be in the area, communicated with the crew of FNA and requested their position. At 0226, as the pilot in command of FNA replied, the pilot in command of FNB saw FNA pass approximately 400 ft below his aircraft on a reciprocal track. FNA was not fitted with a TCAS and the crew of FNA did not see FNB. Flight service had not directed traffic information to either crew.

Flight Service procedures

Both aircraft were outside controlled airspace and operating in a directed traffic information environment in which air traffic control does not provide positive separation between air traffic. However, flight service was required to provide aircraft operating under instrument flight rules information on other possibly conflicting military or instrument flight rule traffic. The requirements and parameters for issuing traffic advice by flight service are in the Manual of Air Traffic Services. The procedures in the manual required the flight service officer to provide traffic information to the crews of both FNA and FNB about each other's flight routes because both aircraft were going to be within 15 NM of each other laterally and FNB was climbing through FNA's level.

When aircraft are planned to depart non-controlled airspace and enter controlled airspace, the flight service officer calculates a release time, which is the time at which the flight service officer expects the pilot of the aircraft to be communicating with air traffic control. When air traffic control receives notification from flight service that an aircraft will be entering controlled airspace, the controller calculates a time of acceptance when the aircraft is expected to be on frequency. Neither the release nor acceptance times are coordinated between flight service and air traffic control.

Flight Service Officer actions

The flight service officer was managing the combined sectors of Flight Service 1 and 8 at the time of the incident. Flight service team leaders were responsible for the administration of shifts. They did not provide active supervision of flight service officers at their work positions.

At the time of the incident, the flight service officer was responsible for monitoring 13 VHF and 8 HF frequencies, and 15 aircraft. Of the 15 aircraft, approximately 10 were active and the remainder were pending. Consequently, the flight service officer and his supervisor reported that the workload was considered light to moderate.

The flight service officer reported that he had assessed that after departure it would take FNB 15 minutes to climb through FL200 into controlled airspace. He therefore calculated that FNB would be in controlled airspace at about 0223 and he rounded up his expected release time to 0225. Air traffic control reported that they added a standard 15 minutes to the departure time advised unless the aircraft was known to have a low performance climb, such as the Fokker 50. In this case, 20 minutes was added. Therefore, the expected on-frequency time for FNB would have been 0228 and in accordance with standard practice, communications checks would have commenced by 0231.

The flight service officer reported that he would have normally passed traffic information to the pilots of both aircraft when FNB taxied at Carnarvon. The flight service officer was unable to explain why he did not believe the two aircraft were potentially conflicting. Following the incident, the flight service officer reported that he thought the Fokker 50 would have climbed at about 1,500 ft/min, a figure he reportedly derived from a previous conversation with one of the operator's pilots. Advice from the operator indicated that it was highly unlikely that a Fokker 50 could achieve such a rate-of-climb, particularly at the flight levels at which FNB was operating. The local flight service management reported that flight service did not advocate calculations based on rate of climb as a traffic assessment method.

The flight service officer reported that he filed the flight strip for FNB soon after the release time of 0225, believing the aircraft to be clear of non-controlled airspace.

Human factors

The flight service officer had received some air traffic control training and reported that he had previously used air traffic control techniques to determine whether traffic was in potential conflict. The use of air traffic control techniques was not required or advocated in flight service procedures. The flight service officer had passed a performance check the day before, when the checking officer noted him using some air traffic control procedures to decide what traffic information should be provided. The supervisor counselled him at the time not to use such procedures. The flight service officer reported that he had been using air traffic control techniques for some time to determine what information needed to be passed to aircraft operating outside controlled airspace in an attempt to reduce the amount of, what he considered, unnecessary radio calls. Although the flight service officer had used unapproved procedures in the past, he did not have any history of providing inadequate or inappropriate traffic information. During the investigation, it was reported that other flight service officers who had undergone some air traffic control training were also known to have applied air traffic control procedures in the flight service environment.

The flight service officer reported that Airservices Australia had managed his career within the previous 2 years in such a manner that caused him concern because there was substantial uncertainty related to his future employment. The flight service officer also reported that as a result of this uncertainty, he was facing significant personal issues and was probably pre-occupied by these issues when he started the shift on the day of the incident. He had approached his local management prior to the incident for leave and the request was being processed at the time of the incident.

The flight service officer reported that he was uncertain about his future employment and as a result of this uncertainty he had only a small amount of sleep the night before his shift and was feeling tired at the time of the incident. The flight service officer's immediate supervisor reported that he was unaware that the flight service officer may have been experiencing significant personal stress or that the flight service officer was fatigued when he commenced duty.

Traffic alert and collision avoidance system

Both aircraft belonged to the same operator. The operator was introducing TCAS as each aircraft underwent a major servicing. FNB was the only aircraft in the operator's fleet that had been fitted with TCAS and not all of the operator's pilots had been trained in the use of TCAS. The operator's policy was that unless both pilots in a crew were qualified to use TCAS, then the equipment was only to be used in the traffic advisory (TA) mode. A TA is indicated on the equipment display to the crew when the aircraft are within about 48 seconds of their closest passing, based on projections derived from current flight path and speed.

The pilot of the Chipmunk did not see the Metroliner. It is likely that the pilot commenced his take-off roll when the Metroliner was at least 3 NM from touchdown. At that distance, the Metroliner may not have been readily detectable by the Chipmunk pilot. His lookout for possible traffic would most likely have been directed towards the circuit and approach of runway 03 rather than towards runway 21 and he would not have been expecting to see traffic approaching from the opposite direction. With the aircraft in the level attitude during take-off, he would have been looking along the runway and his attention would have been focused on maintaining directional control. The Metroliner would most likely have been obscured from the Chipmunk pilot's view by the nose of his aircraft when he subsequently rotated to the climb attitude.

The crew of the Metroliner did not see the Chipmunk until that aircraft was almost overhead theirs. As they had not received any response to their broadcasts on the CTAF, they were relying on visual acquisition of any unalerted traffic as their only defence against a conflict. However, the Chipmunk was a small visual target with little relative movement. In addition, it had no anti-collision lighting and would initially have been below the Metroliner crew's horizon. The contrast between the background and the colour of the Chipmunk was minimal and would have made the aircraft difficult to discern.

The straight-in approach procedure at CTAF aerodromes did not appear to adequately address the limitations of unalerted "see and avoid" principles. The assumption of two pairs of eyes being more likely to detect unalerted aircraft than one pair of eyes, did not prove to be an adequate defence in this incident.

In this instance, the crew of the Metroliner elected to make a straight-in approach in wind conditions that most probably favoured a reciprocal runway direction. Without any response to their broadcast intentions, the crew probably assumed that there was no traffic and believed it was safe to use runway 21. As regulations in force at the time of the occurrence did not include a requirement for an airline operator to assess the circumstances and the likelihood of encountering non-radio traffic at individual locations, it was likely that many crews were conducting straight-in approaches as an expected routine. Had the crew been aware, for example, of the potential for greater numbers of recreational movements at weekends and on public holidays, they may have decided not to conduct the straight-in approach.

Although the company had provided a radiocommunication service to comply with the requirements for this procedure, its effectiveness to alert the crew to other aircraft was restricted by company procedures and by the physical location of the radio operator. The radio operator was not familiar with aircraft movements and had never been instructed to provide runway-in-use information. Had the radio operator been afforded a full view of the entire runway and the approach path of the Metroliner and permitted to issue traffic information, a timely warning may have been broadcast to the crew of the Metroliner about the presence of the Chipmunk.

The pilot of the Chipmunk chose to continue his flight without radio communication and without knowledge of a procedure that could place him in potential conflict with a passenger-carrying aircraft. Knowledge of scheduled aircraft movements at that location may have influenced the pilot to avoid commencing a non-radio flight when the arrival of a scheduled service was imminent.

Sequence of events

The crew of a Metroliner, conducting a scheduled passenger service from Sydney, reported that at 30 NM from Latrobe Valley, they obtained weather information from their ground agent on the common traffic advisory frequency (CTAF). They recorded the wind as light and variable. At approximately 17 NM, the co-pilot broadcast on the CTAF advising their intention to join for a 5 NM straight-in approach to runway 21. Two similar broadcasts were made, one at 10 NM and the other at 5 NM. At approximately 1 NM from touchdown, the crew saw a Chipmunk aircraft a short distance to their left and about 400 ft above them, travelling in the opposite direction. The crew continued their approach and landing as they considered that there was no further risk of collision.

The Chipmunk pilot was conducting a private flight. He reported that the aircraft radio had undergone maintenance prior to the incident flight and that he was unsure if a functional check of the radio had been made. He determined that the wind was a light north-easterly and elected to use runway 03. He broadcast on the CTAF that he was taxiing, and made a further transmission advising that he was backtracking along runway 03. He did not hear any response to either broadcast and had not heard the aerodrome frequency response unit. He assumed that his aircraft radio was not operating and proceeded with the flight without making any further radio broadcasts.

The pilot of the Chipmunk reported that he did not see any aircraft either when entering the runway or when lining up for takeoff. He departed and climbed away, unaware that the landing Metroliner had passed below him. Although he was aware that scheduled flights operated into the aerodrome, he was not familiar with those schedules. He was also unaware that such aircraft could conduct straight-in approaches to CTAF aerodromes. He reported that although his aircraft was equipped with a landing light, he was not in the habit of using it in daylight conditions.

Witness information

An instructor at the aerodrome reported that, at the time of the occurrence, the Chipmunk and the Metroliner were the only aircraft in the circuit. He added that other aircraft movements that day had been made from runway 03.

Following this incident, another instructor observed the straight-in approach procedure under similar conditions. He stationed himself at a position similar to that of the Chipmunk pilot at takeoff in order to determine the visibility of the approaching Metroliner. He reported that when the crew broadcast their 5 NM position, he was only able to see the aircraft after several seconds of looking. However, at an estimated 3 NM, with the landing gear extended and the taxi light illuminated, it was much easier to see the aircraft.

Weather

Weather conditions at the time of the occurrence were described as fine and clear with good visibility. Witnesses on the ground reported the wind as 5-8 kt from the north-east. Data recorded from the automatic weather station (AWS), indicated that a north-east wind had prevailed from 1100 Eastern Standard Time (EST) onwards. The Latrobe Valley METAR (meteorological observation) at 1304 EST indicated that the wind direction was 070 degrees magnetic and the windspeed was 7-10 kt. Those conditions favoured the use of runway 03.

Straight-in approach procedures

On 26 March 1997, the Civil Aviation Safety Authority permitted multi-crew regular public transport aircraft to conduct straight-in approaches to non-controlled aerodromes other than those within a mandatory broadcast zone. Effective from 1 May 1999, amendment 35 to the Civil Aviation Orders (CAO) part 82.3 incorporated a new sub-section 5A that required the provision of a ground-based radiocommunication service at aerodromes where straight-in approach procedures were conducted. However, following industry concerns about the operator's liability in relation to the provision of traffic information and the cost to airlines of providing such a service, that section was amended. CAO amendment 41 was issued with a new sub-section 5B that restricted the information to be given by the radiocommunication service to wind direction and runways in use at the aerodrome.

The company operating the Metroliner contracted the services of a ground-handling and booking agent to perform the required radiocommunication service, and personnel were trained and approved to provide that service. The procedure required the agent's staff to obtain weather information from the AWS and, when requested, broadcast this information to company pilots on the CTAF. Information about other traffic or the runway in use was not transmitted.

The agent advised that crews could obtain traffic and runway information from other aircraft on the CTAF. Other duties performed by the agent's staff precluded them from continuously monitoring the CTAF for information about other traffic. Additionally, the company radio was situated in the airport terminal and only a limited view of the airfield was afforded through the windows. Visual observation of aerodrome traffic from this location was not possible. The Chipmunk would not have been visible from this vantage point at any time it was taxiing or airborne.

There were no specific company instructions for crews making straight-in approaches at CTAF aerodromes. Company management personnel were satisfied that the procedures contained in the Aeronautical Information Publication were adequate. Company standard operating procedures required the landing and recognition lights to be turned on as aircraft were approaching 10,000 ft when transition checks were being completed. The taxi light was not to be turned on until after the landing gear was extended. The crew reported that that procedure had been followed.

The pilot in command advised that the crew's preferred choice of runway direction at Latrobe Valley on the flight from Sydney was runway 21. This not only reduced flying time but also allowed crews the 3-minute cooldown period for the engines while backtracking to the terminal. It also avoided running the engines near the terminal and creating unnecessary noise.

Determination of the runway in use, as required by the Aeronautical Information Publication (AIP) procedure, was assumed by crews to be either the reported runway being used by other traffic in the circuit or, in the absence of other traffic, runway 21, provided that wind conditions were favourable. The view expressed by the pilot in command was that the straight-in approach procedure offered a better level of safety than that provided by the normal circuit entry and that it was more expedient. He believed that the procedure resulted in less circuit manoeuvring and a reduced risk of traffic conflicts.

Aerodrome traffic

This incident occurred on a Sunday afternoon. The airline operated six services per week into Latrobe Valley but only one of these flights was conducted on a weekend. The pattern of activity at the aerodrome was not recorded however, staff at the Aero Club were able to confirm that most recreational flying activity took place at weekends and on public holidays. Only a small number of aircraft operating from the aerodrome were not radio-equipped. The scheduled movements at Latrobe Valley were not published in any of the aeronautical publications.

1. The crew of the Jetstream did not hear the King Air crew's inbound broadcast on the mandatory broadcast zone frequency.
2. The crew of the King Air did not hear the Jetstream crew's taxi broadcast on the mandatory broadcast zone frequency; nor did they hear the transmissions made on the Brisbane control frequency by the air traffic controller that provided essential traffic information regarding the Jetstream, and instructed them to maintain 6,000 ft.
3. The air traffic controller had insufficient time to establish communications with both crews and provide them with sufficient information to enable them to take action to prevent a near collision.
4. The crews had not been alerted to the presence of each other's aircraft.
5. The procedures used in the Demonstration Class G Airspace Trial, which encompassed the Williamtown MBZ and MTA, did not fully consider the impact of radio congestion.

The incident occurred because the crew of the King Air had not been alerted to the possibility of conflicting traffic and continued their descent for Williamtown in the Class G demonstration airspace. The crew had been alerted about another aircraft, a Beech 1900, which was to the north of Williamtown. The air traffic controller believed that the crew of the King Air had been alerted regarding the Jetstream. The controller assumed that he had heard a read back of the level requirement, when in all probability, the controller heard the "two in together" transmission. He also assumed that the King Air would stop descending and maintain 6,000ft. These assumptions were unfounded.

Analysis of the incident highlights problems involving radio communications, attentional focus, workload, and Class G Airspace training and procedures.

Radio communications

The crew of the King Air did not hear the taxi transmission broadcast by the Jetstream crew on the mandatory broadcast zone frequency; nor did they hear the transmissions made on the Brisbane control frequency by the air traffic controller that provided essential traffic information regarding the Jetstream and instructed them to maintain 6,000 ft.

When the crew of the Jetstream made their first "all stations" broadcasts on the national advisory frequency and the mandatory broadcast zone frequency, the King Air was in Class C airspace and its crew were communicating with air traffic control. The crew of the King Air had no reason to be on the national advisory frequency or the mandatory broadcast zone frequency and could not hear the Jetstream's transmissions.

The crew of the Jetstream reported that they were not aware that communication between themselves and the air traffic control agency could be established while on the ground at Williamtown. The establishment of such communication may have alerted the controller to the potential conflict between the two aircraft much earlier than was the case.

Attentional focus

Throughout the sequence of events for this particular occurrence, when monitoring more than one frequency, the crews had to decide upon which frequency to maintain their primary focus in the face of competing cognitive demands.

The crew of the King Air selected and monitored the mandatory broadcast zone frequency at approximately 31 NM south-west of Williamtown, when the aircraft was passing approximately FL 150. This was entirely reasonable, and accorded with the requirements of AIP. (Annex B to AIP Supplement H48/98, paragraph 5.1, and AIP Supplement H66/98 required crews to monitor the mandatory broadcast zone frequency when below the 8,500 ft upper limit of the mandatory transponder area, except when receiving a radar information service.) However, the focus of the crew's attention would have been centred on the transmissions made on the Brisbane Control frequency.

When the crew of the King Air were cleared by Brisbane to leave the control area on descent, their attention would have been focussed on receiving their clearance and providing an accurate readback to air traffic control. Their focus would not have been on monitoring the mandatory broadcast zone frequency. Accordingly, the crew of the King Air did not hear the Jetstream's departure report, which was being broadcast on the mandatory broadcast zone frequency at that time. Moreover, the Brisbane controller's transmission on the control frequency of 126.9 MHz was the only transmission that linked the King Air with the Williamtown mandatory broadcast zone.

The crew of the Jetstream were broadcasting their departure report on the mandatory broadcast zone frequency using their VHF 1 radio. Their attention would have been focussed on their transmission and on handling the aircraft. They had the Brisbane Control frequency of 126.9 MHz selected on their VHF 2 radio, but their focus would have been on their transmission on the mandatory broadcast zone frequency on VHF 1. The crew of the Jetstream did not hear the transmission that "linked" the King Air with the Williamtown mandatory broadcast zone. Such a link may have assisted the crew of the Jetstream to develop a better mental model of the air traffic situation.

Although the crew of the Jetstream were monitoring the Brisbane Control frequency of 126.9 MHz for over 4 minutes prior to their departure from Williamtown, insufficient information was broadcast on that frequency for the crew to develop an accurate picture of the air traffic situation. Notwithstanding the monitoring of the control frequency, the crew's attentional focus during their taxi and departure would have been on any transmissions made on the mandatory broadcast zone frequency.

When the King Air crew confirmed that they were still on the control frequency, the controller gave them traffic information on a Beech 1900. The King Air was passing 8,700 ft on descent when this traffic information was received and focus of their attention was shifting towards the establishment of mutual separation with other aircraft in the mandatory broadcast zone.

The crew of the Jetstream reported their position to Brisbane Centre passing 4,000 ft on climb. During the period of the Jetstream's transmission, the crew of the King Air was making an "all stations" broadcast on the Williamtown MBZ frequency. The crew of the Jetstream did not hear this broadcast because their attention was focussed upon making their report, and reading back the clearance. The crew of the King Air did not hear the Jetstream's transmission because they were concentrating on arranging mutual separation in the mandatory broadcast zone with the Beech 1900.

Weather

The meteorological area forecast for Williamtown and the trend type forecast were not favourable and indicated that an instrument approach would be necessary for aircraft inbound to Williamtown. The actual weather was consistent with the forecast.

Class G airspace

Contributing to the incident was the confusion on the part of aircrew concerning the requirements of the Demonstration Class G Airspace trial. Also contributing, was the fact that the design of the Class G procedures encompassing the Williamtown mandatory broadcast zone and mandatory transponder area did not fully consider the impact of radio congestion.

During the Class G airspace trial, there was some confusion within the aviation community regarding the termination of radar services. The Civil Aviation Safety Authority reviewed the first fortnight of the trial and as a result clarified some of the procedures in "Aiming Higher", vol. 1 no. 8, October-November 1998. In the section "Termination of radar services by Air Traffic Control (ATC)", the article explained that when an aircraft receiving a radar control service leaves controlled airspace and the radar service continued as a radar information service, ATC would advise "Control service terminated". Further, ATC would advise "Radar service terminated" when a radar information service was terminated.

The air traffic controller's transmissions reflected this aircrew confusion. Indeed, his workload was increased because of deficiencies in the education program provided to the aviation community prior to the introduction of the Demonstration Class G airspace. Also, although the crew of the King Air complied with all of the provisions of the AIP, they did not fully understand the procedures to be used when operating in the Demonstration Class G airspace.

The design of the procedures used in the Demonstration Class G airspace did not fully consider the impact of radio congestion. Even though the controller attempted to separate the two aircraft, he was not required to do so in Class G airspace.