Breakdown of co-ordination

At 1550 VH-RUH, enroute Broken Hill to Moorabbin, reported overhead Natya at 7,000 ft. At 1552 VH-LJR, enroute White Cliffs to Essendon, reported overhead Natya, also at 7,000 ft. The Flight Service (FS) 14 operator was expecting LJR to be at its planned level of 5,000 ft. Neither aircraft was aware of the other and traffic information was immediately passed.

Investigation revealed that the pilot of LJR requested traffic for a climb to 7000 ft 16 minutes after departure from White Cliffs. That request was to the FS15 operator. Nine minutes after that request the pilot of LJR reported maintaining 7,000 ft. Departure co-ordination from FS15 to FS14 was done manually because the operators were too busy on their frequencies to do it by intercom. The investigation was unable to determine whether the level change was co-ordinated as part of the departure co-ordination.

The pilot of LJR called FS14 at 1510 (42 minutes before he reported over Natya) and reported maintaining 7,000 ft and an amended estimate for Natya. The FS14 operator did not realise that LJR was no longer at its planned level and the FS14 flight strip still indicated 5,000 ft. When the aircraft later reported at Natya, there was a different operator working the FS14 position. He immediately noticed the aircraft was not at its planned level of 5,000 ft which was still annotated on the flight strip.

Both FS15 and FS14 were very busy at the time. FS15 was dual manned and in addition to normal traffic was handling a difficult distress phase which extended over a protracted period.

FACTUAL INFORMATION

A formation of four Skyhawk A4 aircraft had been flight planned to depart from Nowra on a low-level jet route flight over central New South Wales and then return to Nowra. The flight was notified in accordance with the Manual of Air Traffic Services (MATS) procedures and included a Notice To Airmen (NOTAM) which had been issued the day prior to the flight. The initial track of the flight was from Nowra, direct to Cowra at flight level (FL) 220, after which the formation would descend to low level, outside controlled airspace. The initial segment of the flight was to be conducted in controlled airspace which was the responsibility of a Melbourne based sector controller. The Melbourne sector controller was required to coordinate the flight with Sydney arrivals and another Melbourne sector.

The formation was to be intercepted by another Skyhawk immediately after departure from Nowra. The intention was for this Skyhawk to depart prior to the formation and to hold overhead Nowra. The pilot of this fifth aircraft would then intercept the formation as it departed Nowra. The intercept was planned to be completed by the time the formation reached a point 20 NM north-west of Nowra. This was just inside the area of responsibility of the Melbourne sector controller. The limit of Nowra military controlled airspace, on the planned track, was 15 NM northwest of Nowra. After the intercept, the fifth Skyhawk would continue on the same route planned for the formation.

Notification of the flight of the fifth Skyhawk was included as a note on the flight plan for the formation. The note advised that an aircraft with a callsign "TBA" (to be advised), would operate within 20 NM of the formation and would conduct an intercept of the formation. The flight plan did not state that there would be five Skyhawks or that the intercept would be conducted in the area between Nowra and 20 NM to the north-west. One hour prior to the Skyhawks' departure, Nowra air traffic control (ATC) contacted Melbourne ATC and co-ordinated the expected use of a block level of airspace from FL180 to FL250 for all five Skyhawks during the intercept. The actual levels requested would be co-ordinated when the aircraft taxied.

This was the first time the Melbourne sector controller had experienced an intercept situation and the degree of co-ordination necessary was significantly different to that which he had previously conducted for flights from Nowra. Another controller offered to assist the sector controller, but the offer was declined. The fifth Skyhawk taxied first and was cleared in accordance with the flight plan at FL220. The Melbourne sector controller co-ordinated this clearance with Sydney arrivals.

When the fifth Skyhawk was ready to depart Nowra, ATC co-ordinated the use of a block level. The block level requested was from FL180 to FL250. Nowra ATC advised that the pilot would remain on Nowra's frequency until the intercept was completed. The Melbourne sector controller requested confirmation of the extent of the area required for the intercept and was advised by Nowra ATC that the Skyhawk may require operations between 20 NM and 30 NM from Nowra. The Melbourne sector controller concurred with the use of the block levels. The sector controller did not issue a clearance limit for the aircraft or co-ordinate the use of the block levels with Sydney arrivals.

The Skyhawk formation taxied shortly after and was cleared via the flight planned route at FL220. The Melbourne sector controller co-ordinated the clearance with Sydney arrivals. The fifth Skyhawk became airborne at Nowra and climbed overhead the airfield. Nowra ATC passed radar identification on the fifth Skyhawk to the Melbourne sector controller. Prior to the formation departing, the Melbourne sector controller twice queried Nowra ATC with respect to the actual levels to be used by the two elements of Skyhawks. On both occasions Nowra ATC confirmed that both the formation and the fifth Skyhawk would be operating in the block level from FL180 to FL250 during the intercept.

The Melbourne sector controller advised both the Sydney arrivals controller and the other sector controller that the aircraft would be conducting an intercept and operating in the block level in his sector before transferring to their sectors. The two other controllers requested confirmation that all the Skyhawks would be maintaining FL220 on entering their airspace. The Melbourne sector controller confirmed that the Skyhawks would be at FL220.

The formation of Skyhawks departed Nowra and was transferred from Nowra ATC to the Melbourne sector controller 10 NM north-west of Nowra. The fifth Skyhawk was 8 NM behind the formation and Nowra ATC requested approval to maintain the aircraft on their frequency as the pilot was taking longer than expected to intercept the formation. This was not in accordance with radar control procedures in MATS which require all aircraft being radar separated to be operating on the same frequency. The Melbourne sector controller approved the fifth Skyhawk to remain on Nowra's ATC frequency after confirming that the aircraft was on descent to FL220. Shortly after, the fifth Skyhawk entered the Melbourne sector controller's area of responsibility but remained on a Nowra ATC frequency.

The Melbourne sector controller passed the radar identification of the fifth Skyhawk to the Sydney arrivals controller and advised that the aircraft was on descent to FL220. The Sydney arrivals controller accepted control of the fifth Skyhawk at FL220 and indicated that he was concerned because of a northbound B737 at FL230 that would be crossing the track of the Skyhawks. Traffic information on the B737 was passed to both elements of Skyhawks by the Melbourne sector controller and Nowra ATC. At no stage was the clearance for either Skyhawk element amended to restrict operations, in the block level, to a level that would ensure vertical separation from the B737.

The Skyhawk formation leader sighted the B737, and the pilot of the fifth Skyhawk advised Nowra ATC that he would not climb above FL220. Nowra ATC advised the Melbourne sector controller that the aircraft would not be above FL220. All five Skyhawks then transferred to the Sydney arrivals frequency. The Skyhawks were approximately 50 NM north-west of Nowra.

The pilot of the fifth Skyhawk reported to the Sydney arrivals controller that he was maintaining FL190. This was not the level that had not been co-ordinated by the Melbourne sector controller. The Sydney controller had based vertical separation with other aircraft in his sector on the previously co-ordinated level, FL220. The Sydney arrivals controller instructed the pilot of the fifth Skyhawk to descend to FL180 due to a Saab 340 at FL190. The pilot of the Skyhawk requested FL220 and was subsequently instructed to climb to FL220 by the Sydney arrivals controller. There was no breakdown in separation but there was breakdown in procedures.

ANALYSIS

More specific explanation of the special requirements for the formation flight would have assisted the sector controller to better appreciate the potential separation and co-ordination problems with the flight. This lack of information and the sector controller's lack of experience with this type of operation did not assist in his management of the task. The sector controller compounded the situation by declining the offer of assistance from another controller. This was a further sign of his inexperience.

The expectation by Nowra ATC and the Melbourne sector controller was that the intercept would be completed prior to the Skyhawks leaving the sector controller's area of responsibility. Because of this expectation, the sector controller did not co-ordinate the use of the block levels with Sydney arrivals or the other sector controller. Consequently, as a result of the intercept not being completed at 20 NM from Nowra, the Skyhawk continuing the intercept while remaining on the Nowra ATC frequency and the controller's own co-ordination workload, he was unable to appreciate the developing situation or eventual consequences.

The operation of the two elements of Skyhawks on different frequencies compounded the situation and caused a delay when the Melbourne sector controller attempted to confirm the aircraft were vertically separated from the B737. Retention of all aircraft operating within the particular block of airspace on a single frequency would have provided an improved level of safety for all the aircraft involved.

The lack of specific limits on the airspace to be used for the intercept pre-disposed the controller to losing control of the situation. Despite his obvious apprehension with respect to what was actually planned to occur, he did not impose any limits on the activity. The use of a suitable separation assurance technique or the co-ordination of the use of the block levels with subsequent sector controllers would probably have prevented the occurrence.

SIGNIFICANT FACTORS

1. The Melbourne sector controller lacked experience of this type of operation.
2. There were limited details of the special requirements for the military flight on the flight plan.
3. The sector controller did not co-ordinate the use of block levels with subsequent control agencies.
4. Aircraft did not operate on the appropriate air traffic control frequency.
5. Adequate separation assurance techniques were not used.

SAFETY ACTION

Local Safety Action

The commanding officer of the Skyhawk squadron agreed to issue two flight plans for similar flights in the future and to ensure that more explicit details of the military requirements are provided on the plans.

ACTUAL INFORMATION

The B747 flight was enroute from Sydney to Kansai, via overhead Cairns then A216. The aircraft had been processed by Sydney and Brisbane ATC sectors and transferred to Cairns area. Cairns area radar position was manned by a trainee controller under supervision. This was the first occasion the trainee had manned the console.

The Cairns planner, who prepares flight strips for use by area radar controllers, did not include coordination annotations on the strip. Prior to handing the flight strip to the radar controller the planner should have annotated the strip with a 'B'. The radar controller places ticks alongside the 'B to indicate completed coordination actions. Later, as the aircraft passed overhead Cairns, the training officer and trainee were so engrossed in training aspects that they failed to update the estimate to the next control agency (Brisbane Sector 10).

Overhead Cairns the aircraft was approximately ten minutes earlier than estimated. Consequently, the aircraft transferred to Brisbane sector earlier than expected. Brisbane sector was unable to provide Port Moresby air traffic service with the 30 minutes notice required by international agreement.

There was no breakdown in separation.

ANALYSIS

Brisbane Sector 10 uses procedural control methods and does not have access to radar information. Consequently, if estimates for aircraft transiting the sector are not notified or amended by adjacent sectors, there is no other means for air traffic controllers to maintain the disposition of air traffic.

Aircraft overflying Cairns northbound have approximately 35 minutes flying time before they enter the Papua New Guinea flight information region. The need to provide 30 minutes notice to the PNG air traffic service allows only a short period for coordination to be implemented. In turn, this limits opportunities to alleviate errors should coordination be delayed or fail to be implemented.

The Cairns planner controller was required to annotate each flight strip with a 'B' to indicate a requirement to coordinate with Brisbane Control. Normally, the 'B' would have reminded the radar controller (and trainee) to notify the estimate to Brisbane sector. However, on this occasion the lack of a visual cue and the controller’s pre-occupation with training reduced the possibility of successful point to point coordination to such a degree that the system failed.

Point to point coordination is a logical process for transfer of flight information through an air traffic system. However, the lack of redundancy in the process means that the system fails if voice coordination is not implemented. Overall, the lack of a safety net for point-to-point voice coordination leaves little room for error.

FINDINGS

1. The B747 crew planned and operated the flight as scheduled.
2. The aircraft was accepted by and handed off to Cairns area control.
3. The Cairns planner did not place coordination annotations on the flight strip.
4. Cairns area control failed to update the pilots estimate to Brisbane Sector 10.
5. The aircraft was transferred to Brisbane Sector 10 approximately ten minutes earlier than expected.
6. Brisbane Sector 10 was unable to provide 30 minutes notice to Port Moresby air traffic service.

SIGNIFICANT FACTOR

1. There was a breakdown in point-to-point coordination.

SAFETY ACTION

As a result of the investigation Airservices Australia Northern District has implemented a local instruction for sector controllers. Brisbane controllers are to check with the Cairns planner if an updated estimate for northbound aircraft is not received by an aircraft's Cairns estimate.

FACTUAL INFORMATION

The B747 transferred from Cairns area to Brisbane Sector 10 without prior coordination. Consequently, Brisbane Sector 10 was unable to provide 30 minutes notice of the flight to the next control agency. This was contrary to international agreement.

The Cairns controller misread the flight strip annotations to indicate actions completed.  However, notification of the aircraft's departure by voice communications had not been done. Consequently, Brisbane Sector 10 was not expecting the aircraft when it transferred from Cairns.

A departure message, dispatched via the Aeronautical Fixed Telecommunications Network (AFTN), was received in Brisbane Area Approach Control Centre but was not used to confirm the aircraft's departure with the sector controller.

There was no breakdown in separation.

ANALYSIS

Brisbane Sector 10 uses procedural control methods and does not have access to radar information. Consequently, if estimates for aircraft transiting the sector are not notified or amended by adjacent sectors, there is no other means for air traffic controllers to maintain the disposition of air traffic.

Departures from Cairns to the north have approximately 40 minutes flying time before they enter the Papua New Guinea flight information region. The need to provide 30 minutes notice to the PNG air traffic service leaves approximately ten minutes for coordination to be implemented. The time available provides little room for error should coordination be delayed or fail to be implemented. Additionally, there is no redundancy in procedures to provide a safety net.

The Cairns controller is required to annotate each flight strip with a 'B' to indicate a requirement to coordinate with

Brisbane Control. When an aircraft departs, the 'B' is subsequently ticked when a message is dispatched via the AFTN and, again, when the controller notifies Brisbane by voice. Thus, coordination is complete when the strip is annotated with two ticks.

The controller, on checking all flight strips, misread the B747 aircraft's strip as having two ticks when there was only one. A departure message had been dispatched via the AFTN, but the controller had not notified the departure by voice.

Some controllers use additional methods to assist them in remembering which flight strips require further action. However, in this incident the controller used one method and had no other cues to assist him once he misread the flight strip annotations.

While departure message, dispatched via the AFTN, are received in Brisbane Area Approach Control Centre, they are not passed to sectors to check that coordination has been implemented. Messages are retained for reference only.

Point to point coordination provides a logical process for transfer of flight information through the air traffic system. However, the lack of a backup procedure means that the system fails if coordination is not implemented. The lack of a safety net for point-to-point voice coordination leaves little room for error.

FINDINGS

1. The B747 flight planned and departed Cairns as scheduled.
2. A departure message was dispatched via the AFTN to Brisbane Area Approach Control Centre.
3. The Cairns controller misread the flight strip.
4. The Cairns controller did not notify Brisbane sector of the departure by voice communications.
5. Brisbane Area Approach Control Centre personnel did not use the AFTN departure message to confirm departure with the sector.
6. The aircraft transferred to Brisbane sector without coordination.

SIGNIFICANT FACTOR

1. There was no safety net available to the air traffic system should there be a breakdown in point-to-point coordination.

SAFETY ACTION

As a result of the investigation, Airservices Australia Northern District has implemented a local instruction for Cairns to provide notification of taxi and departure of northbound aircraft, to Brisbane Sector 10.

The B737 aircraft was being radar vectored for an approach to Sydney runway 34. The Approach South controller issued instructions for the crew to expect runway 34 Right and proceeded to transfer the aircraft to the Director for final approach.

The Director vectored the B737 onto base leg and then onto final approach with an instruction to intercept final for runway 34 Left. This runway expectancy was immediately questioned by the aircraft captain as he had briefed his crew for an approach to runway 34 Right.

The Director confirmed that the runway would be 34 Left and commented that he thought the crew had already been given that information. The captain replied that he had not, but that the change to 34 Left could be safely carried out. The aircraft continued its approach and landed on runway 34 Left without further incident.

It was determined that the coordination for the change of runways was carried out between the controllers concerned, but the exact manner in which this was performed was not established. The controllers did discuss the possibility of changing aircraft between the two runways in general terms, but there was no specific reference to this aircraft on the voice recordings. The flight progress strips, which may have provided further insight into this aspect of the occurrence, were not located during the investigation and were unable to be scrutinised.

No definite reason for the failure to advise the crew of the change of runway could be determined.

FACTUAL INFORMATION

At 1116 EST, VH-CZW, operating a scheduled passenger service, left Brisbane for Melbourne on climb to flight level (FL) 350. The aircraft was trailing another passenger jet, VH-TJR, by several minutes on the same route. Both aircraft were correctly processed from Brisbane Sector 2G to Brisbane Sector 2R. At 1131, shortly after crossing the Sector 2G/Sector 2R boundary at approximately 85 NM south of Brisbane, the secondary surveillance radar return from CZW faded from the interim radar display system when the crew inadvertently switched the secondary surveillance radar transponder to STANDBY as the aircraft passed FL311. The climb continued to FL350. The flight was no longer monitored by radar.

Once the aircraft was beyond 30 nautical miles (NM), the interim radar display system was not capable of displaying primary radar returns as a means of observing the aircraft. The loss of the secondary surveillance radar return was not noticed by the controller on Sector 2R. Consequently, no radar hand-off took place when CZW approached the boundary between Sector 2R and Sector 13T. As a result, the aircraft was not transferred to the next radio frequency.

In the absence of a radar hand-off between controllers or a frequency transfer, the Sector 13T controller did not recognise, from the flight progress strip information alone, that CZW was crossing his area of responsibility. As a result, no radar hand-off or frequency transfer took place between Brisbane Sector 13T and Melbourne Sector 16. The aircraft entered Sector 16 airspace without the controller's knowledge. A Melbourne Air Traffic Service Centre standard procedure covering transfer between sectors, relied on co-ordination to activate the aircraft's flight progress strip.

At 1235, at the instigation of the Melbourne Sector 6 controller (the control position beyond Sector 16), efforts began to find CZW. The aircraft was identified on radar about 90 NM south-west of Parkes.

CZW had been invisible to the interim radar display system for 60 minutes, and as a result had been without radar monitoring services and a search-and-rescue watch for that period of time. The planned level, FL350, could have been allocated to other traffic on, or crossing, the route. In addition, the aircraft had flown approximately 400 NM without the safety net provided by the traffic advisory and collision avoidance system which relies on an operating secondary surveillance radar transponder to render the aircraft visible to other aircraft equipped with the system.

The flight crew

The crew were unaware that they were involved in an incident. When interviewed, they could not remember how the transponder had been switched to STANDBY. However, the three-position toggle switch was unguarded and vulnerable to being touched inadvertently. The secondary surveillance radar transponder unit was located in the centre console, the area aft of which was often used to rest papers or place trays.

On this route, aircraft were often left on the one frequency for extended periods, so the lack of a frequency transfer did not alert the crew of CZW. It was not until they had passed abeam Sydney that the captain became uneasy about the lack of a frequency transfer to Melbourne Control. A radio call to Brisbane Sector 2R asking whether they were required to remain on the frequency, resulted in their being transferred to Melbourne Control and being asked for their secondary surveillance radar transponder code. It was then that they noticed that their transponder was in STANDBY.

Interim radar display system (EUROCAT 200 system)

In the interim radar display system, the labels of correlated (controlled) tracks which are not under a controller's jurisdiction are displayed in blue. When these tracks are proposed for hand-off to another Sector, the individual track label flashes on the display of the controller to whom the hand-off has been proposed. If the proposed hand-off is accepted, the colour of the label changes to green and ceases to flash. The accepting controller now has operational jurisdiction of the track. When the system ceases to receive a response from the aircraft's transponder, the track enters a Coasting/Aging state. In the case of correlated tracks, this results in the track data on the radar display, and the border of its Active Flight Plan List (AFPL) window entry changing to a linen colour. Within 45 to 60 seconds all of the track data on the radar display disappears. The aircraft's electronic flight plan (now annotated with an "L" to indicate its Lost status) remains in the AFPL for a parameter time, which in this case was 5 minutes, before disappearing. A controller may not have the flight plan window open on his display and thus could miss the aircraft fading from his jurisdiction. There are no significant attention demanding cues or aural alarms associated with a lost track. Initially, during specific simulated exercises conducted in Brisbane, approximately 70% of experienced controllers had failed to detect fading transponder returns. Because of this result, the "failed transponder" scenario was inserted in training exercises. The detection rate of lost tracks increased markedly when controllers became aware of the system's limitations.

Secondary surveillance radar transponder failure

Anecdotal evidence indicates that secondary surveillance radar transponder failures and lost tracks in the Brisbane interim radar display system were a relatively common occurrence, up to five per week. Local corrective actions prescribed procedures such as reverting to flight progress strip counts versus the number of active tracks on the radar display and extending the history trails to the maximum setting.

Flight progress strips

Flight progress strips are an integral component of any radar system, including the interim radar display system. They provide search-and-rescue watch for aircraft under jurisdiction and serve as a basis for procedural backup in case the radar system fails. The radar controllers at Sectors 2R and 13T were no longer using the flight progress strips to maintain search-and-rescue action or to provide a cross-boundary check for outbound coordination. The Sector 13T controller was unable to recall why the flight progress strips were held at all.

ANALYSIS

Interim radar display system

The Australian air traffic system, of which the interim radar display system is a part, is primarily dependent on secondary surveillance radar for the provision of radar control of aircraft outside primary control zones. When a transponder return is lost from the interim radar display system, the aircraft can disappear unless the controller is vigilant enough to notice the track fading. The display system is unfriendly to users in that the disappearance is subtle and silent. Monitoring is a task to which humans are ill-suited. Also, noticing the absence of previously displayed information is counter to the human psychological makeup as was evident from early simulator exercises where 70% of controllers failed to notice that a track had faded. Humans are far better suited to noticing new information, hence the use in critical systems of alerting devices such as warning bells/buzzers and coloured lights. The interim radar display system fails to provide these cues when a radar return fades.

Flight progress strips

One of the defences to guard against an aircraft return fading unnoticed from the interim radar display system is the monitoring and careful processing of the flight progress strip for each aircraft under control. The Procedural Controller at Sector 2R and the adjacent Sector13T, failed to process the flight progress strip for CZW. They were unaware that the strip also represented the basis of the aircraft's search-and-rescue watch. The Melbourne-based controller of Sector 16 relied on coordination from Sector 13T to activate the flight progress strip and accept the aircraft into his jurisdiction. This procedure was in accordance with procedures current in the Melbourne Air Traffic Service Centre. All three controllers lacked situational awareness considering that CZW and TJR had left Brisbane within minutes of each other and were flying the same route. The flight progress strips for both aircraft were almost identical. The Sector 6 controller was aware that two aircraft were supposed to be close together. He questioned the failure of CZW to appear with TJR, thus triggering a response to find the aircraft. At about the same time, a radio transmission from the crew of CZW caused confusion in the Brisbane Air Traffic Service Centre because a controller shift change had taken place and the flight progress strips had been filed. Consequently, no one had any historical knowledge of CZW and there was no visible record.

The secondary surveillance radar transponder installation

Two deficiencies were noted. The transponder control unit was located towards the rear of the centre console in the cockpit. The control switch was a simple toggle switch with three possible selections, from left to right - transponder 1, STANDBY (centre) and transponder 2. The switch was unguarded and open to an inadvertent knock. Also, the unit lacked any warning device that it was not operating. Very simple transponders used in general aviation have a green lamp which flashes when the unit is being interrogated by a ground-based secondary surveillance radar.

Safety implications of flight without a transponder

The lack of an operating secondary surveillance radar transponder triggered the fading and loss of the aircraft from the interim radar display system. It left the aircraft without an adequate search-and-rescue watch. The aircraft was flying at FL350, but as far as the system knew, this level was available to any other aircraft. A potential for a collision existed. An operating transponder was also an integral part of the traffic alert and collision avoidance system. Without it, other aircraft fitted with the system could not have been alerted to the aircraft's presence or taken collision-avoiding action.

SIGNIFICANT FACTORS

1. The crew of CZW inadvertently switched the secondary surveillance radar transponder to STANDBY.

2. The transponder switch was unguarded and lacked an interrogation light.

3. The transponder return faded from the interim radar display system.

4. The Interim Radar Display System lacked adequate or significant warning devices to alert controllers that a transponder return had faded.

5. The loss of transponder return went unnoticed by the Sector 2R controller.

6. The Sector 2R Procedural controller did not process the flight progress strip for the aircraft correctly.

7. The Sector 13T controller did not become aware that the aircraft was due in his sector.

8. The Sector 13T controller did not process the flight progress strip for the aircraft.

9. The Sector 16 controller did not become aware that the aircraft was due in his sector. 

10.The Sector 6 controller alerted the air traffic control system that the aircraft was missing.

11.The flight continued for 60 minutes without the air traffic control system noticing its absence. During this time the aircraft was without an adequate search-and-rescue watch and was flying at an unguarded flight level. 

SAFETY ACTION

As a result of the investigation into this occurrence, the Bureau of Air Safety Investigation issued the following interim recommendations:

IR 950230 issued 29 November 1995

"The Bureau of Air Safety Investigation recommends that:

Airservices Australia modify current loss of secondary surveillance radar transponder return procedures to ensure that any loss of secondary surveillance radar transponder signal results in immediate attention-demanding visual cues and aural alarms at the relevant controller processing and displays areas within the national radar system. The modifications should incorporate requirements for the controller to acknowledge the aircraft status change".

Airservices Australia responded on 27 January 1996.

"This recommendation is subject to ongoing investigation, and a resolution is not expected by the response due date. Airservices notes that the recommendation would be equally applicable to AUSCATS as it is to IRDS. In the interim, a software modification to IRDS will be installed in early February. This modification will change the location of "LOST" flight plans to the top of the Active Flight Plan List (AFPL), as is the case in AUSCATS.

"Airservices request an extension to IR950230 to mid-February 1996, to enable a fuller response to the recommendation".

Airservices subsequently responded again on 21 August 1996.

"Re: Occurrence 9502038 generating Interim Recommendation: IR 950230

"Investigation of the subject Interim Recommendation as a viable contributor to preventing a re-occurrence of the incident on which the Recommendation was based has recently been completed. This investigation was conducted in parallel with the introduction of a series of measures designed to enhance controller recognition of the loss of transponder replies from aircraft under jurisdiction within the EUROCAT 200 system operations environment.

"It is believed that these measures, which have involved software and operating procedure changes and the conduct of an incident-specific human factors review in the Brisbane Area Approach Control Centre, are satisfactorily achieving this enhancement.

"Relevant software changes which have been implemented include:

"a. Display of "Lost" flight plans at the top of page 1 of the controller's Active Flight Plan List (AFPL) window so that they will normally always be in view;

"b. Increasing the lost time parameter (which determines how long the lost plan is displayed in the AFPL) from 5 minutes to 10 minutes;

"c. The disabling of the history dot key on controller workstation keyboards so that history dots are always selected (as history dot selection contributes to the time taken for a track to age out and therefore the time the Age symbol [visual cue associated with transponder loss] is displayed); and

"d. Changing the range of history dots which can be selected to 5-9 in lieu of 1-9 (to help maximise the amount of time the Age symbol is displayed to the controller).

"Investigation of the type of software change described in the Interim Recommendation determined that it was both impractical and operationally unacceptable. Several other software change proposals were identified by the relevant Airservices' system specialists in conjunction with affected operations staff, and Thomson Radar Australia (the system supplier). However, the estimated cost of trying to implement the preferred of these proposals was in the order of $250,000 to $260,000.

"A decision has now been taken that no further system related changes be pursued in relation to this matter. This decision was made on the basis that:

"a. Given the remaining operational life of the system, and the very low frequency with which such incidents are reported to occur, cost/safety benefit analysis would not support this level of expenditure;

"b. Even if funding approval could be obtained, the enhancement could not be implemented before late 1996 / early 1997, thereby further reducing its cost/safety benefit;

"c. Change proposals for all Airservices' systems are being critically examined for their potential to impact adversely on the introduction of The Australian Advanced Air Traffic Control System, which (in human resource terms) would be the case with the proposed enhancement;

"d. "Lost" processing related changes (as described above) were successfully introduced in software Release 6.0 in February this year;

"e. ATS Northern District has:

1. amended and/or reinforced relevant Brisbane enroute sector operating procedures and techniques; and
2. introduced transponder failures in simulation exercises.

"f. The recommendations from an ATS Northern District Interim Radar Display System (EUROCAT 200) Human Factors Review (currently being finalised) are expected to provide further practical assistance in this matter, including in relation to the roles and responsibilities of existing Executive and Planner positions".

Response status: CLOSED - ACCEPTED

IR 950192 issued 15 September 1995

"The Bureau of Air Safety Investigation recommends that the Civil Aviation Safety Authority review the design suitability of aircraft transponder control panels fitted to aircraft which operate within Australian airspace. The review should consider mandating:

"(i) selector switches which are designed to prevent unintentional deselection of a serviceable transponder, and

"(ii) the fitting of a device to alert flight crew that a transponder has been selected to off or standby or has become unserviceable".

The Airservices Australia response received 16 November 1995 stated:

"Re: IR950192

"Airservices Australia supports this BASI recommendation.

"We have experienced a number of transponder difficulties caused by inadvertent crew action. This recommendation simply and effectively addresses these problems".

On 23 November 1995, the Civil Aviation Safety Authority indicated:

"I refer to your interim recommendation number IR950192 concerning an incident involving Boeing 737, VH-CZW transponder error on 5 July 1995.

"Summary

"The Authority does not accept the recommendation in light of the costs and alternative measures available.

"Background to response

"The cost of implementing the recommended modifications on all Australian registered aircraft fitted with Air Traffic Control Transponders would be excessive. A less costly modification to the software of the secondary surveillance radar displays could ensure that the "Lost" aircraft transponder message is highlighted to the controller. Procedures could also be initiated whereby the controller must respond to the message.

"This matter will be referred to Airservices Australia for information and comment".

Response status: CLOSED - ACCEPTED

BASI NOTE:  As a result of this occurrence, the operator advised that all aircraft with similar switches were modified to prevent inadvertent deselection of a servicable transponder.

IR 950210 Issued 27 November 1995

"The Bureau of Air Safety Investigation recommends that Airservices Australia, in conjunction with the Civil Aviation Safety Authority, publish consolidated documentation for flight crew use which indicates the primary and monopulse secondary surveillance radar coverage, enroute reporting requirements and the importance of ensuring continuous transponder activation in the present radar environment".

Airservices Australia response received on 31 January 1996 stated:

"Airservices is giving consideration to re-instituting a chart of radar coverage, similar to that which used to exist in

Aeronautical Information Publication. Any such chart shall contain a note referring to Aeronautical Information Publication documentation which details the pilot reporting requirements and the transponder activation requirements. With regard to transponders, the instruction to pilots is that "Unless advised otherwise by ATC, pilots of Mode 3A transponder equipped aircraft operating in Australian airspace must activate their transponders, and where a Mode 3C capability is also available it must be activated simultaneously with Mode 3A"."

Response status: CLOSED - ACCEPTED

Civil Aviation Safety Authority response received 18 February 1997:

"In relation to IR950210 regarding the importance of transponder activation, CASA is giving consideration to appending two notes to AIP RADAR-8 para 72.2.  One would highlight the importance of transponder activation advising that primary radar coverage only exists within 50nm of major airports and that the remainder of the radar system relies on transponder information.  The other would highlight the importance of activation of the transponder for the avoidance of collision through TCAS."

Response Status: CLOSED-ACCEPTED

IR 950211 issued 27 November 1995

"The Bureau of Air Safety Investigation recommends that:

"Airservices Australia and the operating companies jointly provide consolidated frequency selection documentation for in-flight use by flight crew. Such information should indicate a failsafe frequency selection sequence to follow in the event of human or ATS system failures."

The Airservices Australia response received 31 January 1996 stated:

"Airservices Australia does not fully support this recommendation as the question of who has authority to manage the time or place of a frequency change must be answered. Good practice and safety management require that there is no confusion as to who initiates a frequency change. This responsibility must reside with the controller to avoid frequency changes unbeknown to the system. However, as a planning guide for pilots about when frequency changes would normally occur, there is merit in the recommendation.

"Flight Information Area boundaries are currently shown on enroute low charts, due to the combined functionality this chart now has for Instrument Flight Rules and Visual Flight Rules pilots. Sector boundaries and frequencies were, at one time displayed on the Planning Chart Australia. However, the amount of detail that is now displayed on the Planning Chart has increased, which would mean the inclusion of sector boundaries and frequencies would significantly clutter this chart. The continuing consolidation and rationalisation of air traffic control sectors require a more dynamic means of providing up to date consolidated information. This is presently achieved by the issuing of Aeronautical Information Publication Supplements.

"Airservices notes that the Civil Aviation Safety Authority does not support the depiction of sector boundaries and frequencies on high level charts, due to chart clutter, particularly along the eastern seaboard of Australia.

Additionally, it is Airservices understanding that major Australian operators and overseas operators utilise Jeppesen charts.

"Airservices has sought comment from Qantas and Ansett on this proposal, and await their reply".

Response status: CLOSED - ACCEPTED

IR 950221 issued 27 November 1995

"The Bureau of Air Safety Investigation recommends that the Civil Aviation Safety Authority amend published procedures to require all aircraft operating within controlled airspace to report reaching an assigned level." Civil Aviation Safety Authority response received 5 March 1996:

"CASA does not support the recommendation that procedures be amended to require all aircraft operating within controlled airspace to report reaching an assigned level.

"Aircraft are not required to report, after having been radar identified, while within radar coverage. The logic being that position information, including the level at which the aircraft is flying, is continuously available to the controller. While reporting top of climb would provide an additional reminder to ATS to check an aircraft's position, so would reports at each of the designated reporting points on the aircraft's route of flight. However, without other cross checks, an aircraft could disappear from the radar screen shortly after having made any report and the fact not be noticed for a considerable period of time. The solution of this problem requires that ATS have in place a means of ensuring detection of aircraft which disappear from radar screens. Such a means is, in fact, part of the radar system and cross checks are incorporated in ATS procedures as a back-up. However, there is a problem with this particular radar system indication and the ATS back-up procedures were apparently not applied to the flight in question. CASA has been advised that ATS is taking action to rectify the system indication problem and ensure controller compliance with procedures requirements."

Civil Aviation Safety Authority subsequent response received 18 February 1997:

"IR 950221 recommends pilot reporting of reaching an assigned level. This recommendation does not address the issue of immediately alerting the controller to a loss of a transponder symbol, at any time during flight. Such alerting must be achieved by means of radar display systems and controller procedures, not by pilot/controller interactions which may not identify the failure till some time after the event. It is noted that, in the response to BASI IR 950230 (Closed- Accepted). Airservices has listed the actions taken in regard to radar systems and controller procedures."

The Airservices Australia response received on 31 January 1996 stated:

"This recommendation is not supported. The improved radar data systems now available enable a better use of Mode C information, negating the need for ATC to request levels from pilots, thereby reducing frequency congestion. In the procedural environment, level checks are only instigated as required to resolve particular separation conflicts.  Airservices notes that in this incident the subject aircraft was cruising before the next sector."

Response status:  CLOSED - ACCEPTED.

The crew of PAL210 transferred from Melbourne Control (Sector 6) to Brisbane Control (Sector 5) at 1523 hours. On first contact with Brisbane Control, they advised an estimate of 1527 hours for Cunnamulla. The Brisbane controller had not received co-ordination from Melbourne Sector 6 on the prior position of the aircraft. He only held an estimate based on the departure time and the flight plan time intervals. That estimate was 1534 hours.

Investigation revealed a breakdown had occurred at Melbourne Sector 6, the control position responsible for the co-ordination. This had happened at the time of hand over of responsibilities at the end of a shift. The controller going off duty indicated to the controller coming on duty the need for co-ordination in respect of PAL210 but the manner in which he did this was misinterpreted by the on-coming controller and the required co-ordination was not done.

Significant Factor

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

1. A misunderstanding occurred between the controller going off duty and the controller coming on duty.

The aircraft departed Brisbane for Cairns at 0343 UTC, cleared at FL330. This level was coordinated by the Brisbane Sector 7 Procedural Controller to Townsville Control. At 0435 UTC, the Sector 3 Radar Controller contacted the Sector 7 Radar Controller requesting a level change for the aircraft to FL350. This was approved and the aircraft was recleared at FL350. However, the level change was not coordinated with Townsville Control who were still expecting the aircraft at FL330. At the same time, the level change was not recorded on the flight strip for the aircraft. The request from Sector 3 concerning the level change was not heard by the Sector 7 Procedural Controller as there is no facility for that person to monitor the radar controller's hotlines.

VH-CZI was a substitute aircraft for VH-CZC which had been originally planned to operate the flight Sydney to Canberra.  Because no modification message had been originated, the Canberra aerodrome controller (ADC) was neither expecting a call from, nor held a flight progress strip (FPS) for, VH-CZI.

The Canberra approach (APP) controller, located in the Melbourne Area Approach Control Centre (AACC) since

July 1994 attempted a voice co-ordinated hand-off of VH-CZI to the ADC at approximately 30 nautical miles (NM) from Canberra.  The ADC was busy on another task at the time, so he instructed APP to standby.  APP terminated the Canberra call and dealt with other traffic co-ordination.  Although the hand-off of VH-CZI was not completed, the FPS was annotated as though the co-ordination had been completed, without restrictions imposed by the ADC.  APP continued processing VH-CZI for a visual right circuit for runway 35 at Canberra in the normal manner.  About this time there was a change of ADC personnel and neither the uncompleted co-ordination exchange nor the presence of VH-CZI entering the circuit area were noted.

APP then transferred VH-CZI to the Canberra ADC frequency, but the aircraft had a minor radio problem during the transfer which did not significantly affect the actual frequency transfer.  Subsequently, the first communication from the aircraft to the ADC was in the nature of a radio communications check, rather than a normal base report and was insufficient to cause any concern.  The call could have had its origins from the aircraft located anywhere within VHF range of the ADC frequency such as would occur from an aircraft within approximately 200 NM if overflying at high level. The initial radio check call was then followed by a call which alerted the ADC that VH-CZI was in fact on right base for Canberra runway 35.  Until that time, neither the former nor latter ADC had been aware of VH-CZI.

Hard copy departure (DEP) messages are required to be originated for all regular public transport (RPT) flights. Sometimes the DEP messages are delayed to the extent that voice co-ordination occurs first due to the short flight time involved between Sydney and Canberra.  On this occasion, a modification (CHG) message, advising of the aircraft substitution, should have been generated when first advice was received.  But this was not done, presumably because of either the short flight time intervals or the intention to include the CHG information in the DEP message. It is standard operating procedure (SOP) for APP to co-ordinate estimated times of arrival (ETA) to the ADC for all arriving aircraft with a flight time of 30 minutes or less, unless a hard copy message has been generated.

The SOPs also prescribe that inbound aircraft are transferred from APP to ADC at about 40 NM, where aircraft normally become visible on the ADCs non labelled radar display. In the prevailing visual conditions APP was required to obtain any restrictions for further descent for inbound aircraft from the ADC.  At the time of the incident, there was no standard phraseology indicating absence of a descent restriction.  This situation has since been rectified by the Civil Aviation Authority.

New technology radar facilities with jurisdictional label displays are programmed for commissioning in the Canberra control tower early in 1995. Provision of new radar facilities will not remove the necessity for failsafe transfer of jurisdiction SOPs between APP and ADC because of the requirements for the ADC to maintain continuous visual surveillance of circuit traffic.

CONCLUSIONS

Findings

1. A modification message advising of the aircraft substitution was not originated.
2. The approach controller terminated the co-ordination call and then incorrectly notated the flight progress strips to indicate that transfer of jurisdiction was completed.
3. Neither the uncompleted co-ordination nor the presence of the aircraft entering the circuit area were detected during the transfer of responsibilities between the aerodrome controllers.
4. The first communication from VH-CZI to Canberra tower was insufficient to alert the controller to the presence of the aircraft in the circuit area.
5. The standard operating procedures prescribed for jurisdiction transfers were not failsafe.

SIGNIFICANT FACTORS

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

1. There were inadequate back-up procedures to prevent degradation of system safety levels caused by delays or omissions in generating hard copy modification and departure messages.
2. The existing control tower radar display facilities and co-ordination procedures were inadequate to alert the controller/s to the inbound aircraft.

SAFETY ACTION

As a result of this investigation the Civil Aviation Authority has introduced standard phraseology for co-ordination exchanges where descent restrictions have not been imposed.

As a result of this investigation, the Bureau established that pending system changes by the Civil Aviation Authority would provide fail safe back-up procedures to prevent similar occurrences caused by delays or omissions in generating hard copy modification and departure messages.  The outcomes of the system changes would be monitored for effectiveness by both organisations.

When the AFTN strip was made up from the aircraft's flight plan, the flight data officer did not designate the route by inserting the correct address code. When another flight data officer came to transmit the AFTN message he noted that the address code was missing. Instead of checking the flight plan he apparently made a best guess using the departure and destination aerodrome information. However, he guessed the wrong route. Consequently, some of the addressees were omitted, including the Townsville arrival's position. When the B747 departed from Brisbane, a departure message was also not sent to the Townsville arrival's controller.

When the aircraft came within the sector seven controller's jurisdiction he omitted to annotate his flight strip with the updated estimated time of arrival for the aircraft. This mistake was not recognised and coordination for the aircraft with the Townsville arrival's controller was not accomplished. The omission was not noted until the Townsville arrival's controller asked about an unknown aircraft entering his airspace from the south-east. The B747 had been maintaining 31,000 ft and there were no conflictions with other aircraft.

The sector was busy at the time with congested traffic in the Mackay/Whitsunday area which included an international aircraft with radio communications problems and unnotified light aircraft traffic asking for clearances at the new airspace boundaries in the Mackay area. While all the controller's attention was focused on this area, the high altitude B747 was overlooked.

The radar and procedural sector seven consoles were manned with a trainer and trainee at each console. The radar controller was undergoing a final check before being rated on the position. The radar console also suffered from some ergonomics deficiencies. The coordination intercom line was not operating, and the hand operated radio transmission switch was unserviceable. The radar operator had to lean across the procedural console to use its coordination line. The training was also a distracting factor because of trainer/student interaction and as a result the controllers had less opportunity to monitor each other.

The procedural console was manned by a trainee and trainer who had not operated together before. The trainee was being shown a method of laying out his flight strips which involved an altitude ranking rather than a chronological order as previously used by the trainee and his full-time instructor. This disrupted his scanning technique.

The complex combination of factors resulted in a lack of coordination between the various air traffic service units responsible for the supervision of the B747 flight.