Loss of separation

After departing Sydney, the SAAB 340B was being radar vectored to intercept the 297 radial whilst maintaining 5,000 ft. The BAE146 was on a right circuit for runway 16R, and had been assigned 6,000 ft. The departures radar controller subsequently noticed the altitude readout of the BAE146 indicating 5,500 ft and passed traffic information to the SAAB. The BAE146 was then observed to climb back to its assigned altitude.

An examination of recorded radar data indicated that the BAE146 had descended to 5,600 ft. As a result, vertical separation between the aircraft was reduced to 600 ft, with a horizontal separation of 1.4 NM. The required minimum separation standard was either 1,000ft vertically, or 3 NM horizontally.

The captain of the BAE146 subsequently reported that the first officer was the handling pilot and was under training at the time of the incident. He had observed the aircraft to descend below the assigned altitude and informed the handling pilot of the error. The aircraft was then climbed back to its assigned altitude.

The crew of VH-KDO were given a runway 16 Strathbogie standard instrument departure (SID) and were told to maintain 3000 feet. After take-off they were cleared to climb to 4000 feet.

Shortly afterwards, the air traffic controller noticed the transponder mode C altitude readout increase to above 4000 feet. When the crew were queried on the altitude deviation they promptly descended back to 4000 feet. However, a loss of separation occurred with VH-JQF, an Airwork aircraft, tracking in an easterly direction to the south of Melbourne and maintaining 5000 feet.

Significant Factors

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

1 The crew of VH-KDO did not maintain the assigned altitude of 4000 feet.

Factual Information

VH-MWG had departed Armidale for Wollongong and was maintaining 10,000 ft outside controlled airspace.  The crew reported at Armidale east at 1244 ESuT, with an estimate for Mount Sandon at 1303.  The Flight Service Officer (FSO) passed conflicting traffic information on VH-DMI to the crew of MWG.

DMI had departed Sydney for Armidale and was maintaining flight level (FL) 190 in controlled airspace.  The crew reported their position to sector control as passing West Maitland at 1228, with an estimate for Armidale of 1258.

At 1233, the sector controller passed the DMI position report to the FSO and coordinated the frequency transfer as vacating FL 190.  The FSO considered that, as DMI would need to descend 9,000 ft prior to leaving controlled airspace, there was sufficient time to pass traffic information on MWG after the crew of DMI had transferred to her frequency.

At 1247, the crew of DMI requested descent into Armidale and were cleared to leave control area on descent by the sector controller.  The crew commenced descent a few seconds later but did not report leaving FL 190.

Although the altitude readout for DMI was displaying correctly on the radar screen, the controller did not notice that DMI had left FL 190 and did not instruct the crew to change to the flight service frequency.

At 1251, the FSO contacted sector control to find out the actual position of DMI. She had realised that the time by which she had expected the crew to call had expired and the traffic information on MWG had still not been passed.

The controller then looked at the radar screen specifically to fins DMI and noticed that the aircraft was descending through FL120.  He also noticed a conflicting aircraft 4 NM ahead and on a reciprocal track and informed the FSO.

The FSO confirmed that the conflicting aircraft was the one she wanted to pass as traffic to the crew of DMI. 

During this discussion, the sector controller instructed the crew of DMI to transfer to flight service on 122.1 Mhz. He did not pass the traffic information at that time, but did pass traffic a few seconds later.  However, the crew of DMI had already changed frequency prior to those instructions.

As they approached 11,000 ft, the crew of DMI realised that they needed to contact flight service prior to leaving controlled airspace and initiated a call to sector control.  This call was made at the same time as the sector controller had initiated his call to DMI and consequently neither party heard the other transmit.

As they passed 10,800 ft, the crew of DMI sighted MWG and adjusted their flight path to pass behind that aircraft.

Radar analysis indicates that the aircraft passed by 500m horizontally, with no vertical separation.

Analysis

The sector controller normally waited for a pilot to report leaving a level before instructing the crew to change frequency.  In this case, the crew did not make this required report and the reminder to the controller was lost.  At the same time, the controller became occupied with other tasks and did not notice that DMI was on descent.

The crew of DMI were required to leave FL 190 within one minute of the instruction from sector control and to report leaving that level.  The controller is required to check that the aircraft has commenced its descent if no such report is received.  This check may be carried out by reference to radar information.

The FSO had correctly calculated the confliction between DMI and MWG and needed to pass traffic information to each crew.  However, she was cognisant of the historical adversity that air traffic controllers had to passing such information on control frequencies.  She considered that 9,000 ft of descent gave sufficient time to allow the crew of DMI to contact her, receive the traffic advice and make any operational decision.  Therefore, the FSO decided not to ask the sector controller to pass the traffic information on MWG to the crew of DMI.

The FSO had only recently obtained her rating on the FIS 3 circuit and, although instructions on the passing of traffic information to aircrew via air traffic control existed, she was not familiar with them and had not had them made available to her during training.  These instructions were contained in the Temporary Local Instructions book which was not readily available for officer reference.

Findings

1. The Temporary Local Instructions book was not readily available for FSO reference.
2. The training of FSOs at Sydney did not adequately cover temporary local instructions in relation to the passing of traffic information.
3. The FSO correctly calculated the need for traffic information to be passed to the crews of MWG and DMI.
4. The FSO did not pass traffic information to the crew of DMI at the earliest possible opportunity.
5. The crew of DMI did not report leaving FL 190.
6. The sector controller did not check whether the crew of DMI had commenced descent after no report had been received within one minute of issuing the clearance.
7. The sector controller did not notice that DMI was on descent.
8. The sector controller did not instruct the crew of DMI to transfer frequency to flight service at the coordinated time.
9. The crew of DMI sighted MWG and adjusted their flight path to ensure separation from that aircraft.

Significant Factors

1. Traffic information on MWG was not passed to the crew of DMI at the earliest possible time.
2. The crew of DMI were not transferred to the flight service frequency at the appropriate time.

Safety Action

As a result of the investigation, Sydney flight service management have:

1. Re-issued instructions on the passing of traffic information through air traffic control;
2. Updated the Temporary Local Instructions book and relocated it in a readily available position;
3. Instructed training officers to ensure that all trainees are instructed in all matters included in temporary local instructions; and
4. Introduced new sign-on rules that require all FSOs to read temporary local instructions prior to commencing duty each shift.

FACTUAL INFORMATION

The Piper Navajo Chieftan (PA-31) was inbound to Perth from the south and was descending to 4,000 ft. The approach west controller (AppW) initially intended to put the aircraft onto a right downwind for runway 21; however, due to traffic near the city, he co-ordinated with the approach east controller (AppE) for the aircraft to track via a left downwind. This was accepted by AppE and the pilot was transferred to his frequency at 1213 WST.

The Boeing 767 (B767) was taxiing for runway 21 for a departure to the west. At 1220, AppW advised the aerodrome controller that the departure clearance for the B767 was to maintain runway heading and to maintain 6,000 ft. This clearance was issued to the crew at 1221, when the B767 was cleared for take-off.

At the same time, and with the aim of expediting its landing, AppE arranged with AppW for the PA31 to change to a right circuit for runway 21. The aircraft was still south of the airport when AppE advised the pilot of this change and instructed him to turn left onto a heading of 340 degrees and to descend to 2,500 ft.

At 1223, the aerodrome controller contacted AppE and asked what the intention was with the PA31. Shortly after, AppE noticed an aircraft (the B767) departing and asked AppW what instructions the crew had received. Almost simultaneously, the aerodrome controller contacted AppE and told him to turn the PA-31. AppE immediately instructed the PA-31 pilot to turn right onto a heading of 070 degrees and asked if the pilot had the B767 in sight. The pilot replied that he did.

AppE then asked the tower to maintain the B767 at 2,000 ft. The aerodrome controller instructed the crew of B767 crew to turn right onto a heading of 240 degrees and then informed AppE that he could provide visual separation. The two aircraft passed with approximately 1 NM lateral separation and 300 ft vertical separation.

ANALYSIS

Approach/Departure controllers record information on flight progress strips to assist in the processing of aircraft. AppE and AppW sit side by side and use a common central strip holding bay for the display of active strips. A feature of this display is a "next" designator which houses the current arrival/departure sequence. When busy, this bay can become overcrowded with strips, and they are often placed elsewhere on the console for convenience. AppW could not recall whether the strip for the B767 had been placed under the "next" designator in the central bay. AppW omitted to take the B767 into consideration when he gave approval to AppE for the PA-31 to track for a right downwind for runway 21.

AppE was unsure of the position of the strip for the B767 or whether he had looked at the "next" designator bay prior to co-ordinating a change of circuit direction for the PA-31. The alteration of the track of the PA-31 resulted in the tracking of the aircraft across the departure track of aircraft taking off from runway 21.

SIGNIFICANT FACTORS

1. The procedures adopted by the approach east controller resulted in the PA-31 being directed to track across the departure path of aircraft departing from runway 21.
2. The approach west controller overlooked the impending departure of the B767 from runway 21 when he approved the request from the approach east controller to track the PA-31 for a right downwind for runway 21.
3. The central strip holding bay on the approach console was overcrowded and did not readily indicate all aircraft pertinent to the traffic situation.

SAFETY ACTION

As a result of the investigation, several safety actions were initiated by both Airservices Australia and the Bureau.

Airservices Australia

Instrument departure procedures for Jandakot aerodrome have been published which have minimised the variation of random departure paths.

Bureau of Air Safety Investigation

The Bureau issued interim recommendation IR960044 on 14 May 1996.

"IR960044

"The Bureau of Air Safety Investigation recommends that Airservices Australia conduct a review of Perth terminal airspace and procedures with a view to reducing the number of conflicting flight paths and the amount of intra-unit co-ordination. Such a review should include:

-jurisdiction over the runway heading departure track from each runway;

-airspace division between the approach/departure control positions;

-improved SID/STAR interface; and

-the introduction of standardised holding patterns."

Airservices Australia replied on 16 June 1996 as follows:

"I refer to your Air Safety Recommendation No. IR960044 involving VH-NMP and V8-RBH at Perth and concur with the recommendations.

"Your Interim Recommendations to review aspects of Perth Terminal Airspace and Procedures have generally been addressed. Ongoing planning of the revised airspace and procedures under ROTAP (Restructure Of Terminal Area Perth) will reflect other recommendations provided they are predicted to be compatible with forthcoming and future developments of the ROTAP structure requirements.

"The introduction of additional outer holding patterns is under consideration. Prior to any selection of holding points, a full assessment of any implications as to their placement will need to be made to ensure compatibility with the future airspace revisions.

"SID and STAR changes have been actioned under ROTAP, an Environment Impact Statement has been submitted, and implementation is planned for December 1996. This will provide an improved interaction of Arrival and Departure traffic at Perth.

"Temporary Local Instruction (TLI) WADO/95/023, issued 20 Dec 1995, redefines the areas of responsibility.  A more comprehensive documentation of procedures and airspace divisions will be incorporated progressively with ROTAP amendments.  The TLI addresses:

• enhancements to jurisdiction over the runway heading departure tracks from each runway;
• enhancements to airspace division between Approach East and Approach West, and Departures Control positions;
• Procedure, Co-ordination, and flight Progress Strip annotation requirements."This response was classified as CLOSED - ACCEPTED.

Other aspects of the investigation involving the provision of radar advisory services by approach/departure control are still being researched by the Bureau and any safety outputs from this research will be published in the Quarterly Safety Deficiency Report.

The Chieftain departed from runway 16R on a Radar 6 departure. After initial vectoring to avoid noise sensitive areas, the aircraft was vectored to intercept the planned track to Katoomba and instructed to climb to 5000 ft.

The SAAB was cleared to Sydney via the Oakdale 2 arrival and had been cleared for descent to 6000 ft. The departures controller reported that he observed the Chieftain climb through 5000 ft, in close proximity to the SAAB. He immediately instructed the pilot of the Chieftain to descend to 5000 ft and vectored the aircraft away from the SAAB, as well as passing traffic information on that aircraft. The approach controller notified the pilot of the SAAB, regarding the Chieftain, and vectored the SAAB away from the other aircraft.

Subsequent investigation revealed that the Chieftain had passed within 1.7 NM of the SAAB, with a vertical separation of 900 ft, resulting in a breakdown of separation. At the time of the occurrence the minimum required separation standard was either 3 NM laterally, or 1000 ft vertically.

VH-OJD was cleared to track inbound via the 229 VOR radial on descent to 6,000 ft. The Approach South radar control sector controller (APP S) was processing the aircraft for landing on runway 16R. Due to operational requirements, the APP S controller delayed turning the aircraft onto a right downwind for that runway.

VH-OLN had departed runway 16R, cleared initially to climb to 5,000 ft. The Departures South radar control sector controller (DEP S) cleared the aircraft for an early right turn and an unrestricted climb to its planned cruising level.

The APP S controller was about to instruct the crew of VH-OJD to turn onto right downwind for runway 16R when he recognised that VH-OLN was climbing through 5,000 ft. In an attempt to maintain lateral separation, he instructed the crew of VH-OJD to turn left immediately and advised them of the traffic ahead to their right. At this time, the crew of VH-OJD advised that they were complying with a TCAS Resolution Advisory and climbing to 7,000 ft.

Recorded radar information indicated that the aircraft had closed to approximately 2.1 NM, with 400 ft vertical separation when the minimum separation should have been 3 NM or 1,000 ft vertically. Each had penetrated their respective airspace boundary buffer.

The runway 16 airspace agreement has a narrow corridor in the APP S airspace to the west of the airport. This airspace design limits the flexibility available to APP S when vectoring aircraft to downwind for runway 16. The latitude that DEP S may apply when vectoring departing aircraft onto south-westerly headings, and providing climb, is also restricted.

Separation was not ensured before VH-OLN was cleared for an unrestricted climb. The situation was worsened by the high rate of climb achieved by VH-OLN.

Findings

1. The unrestricted climb instruction provided to VH-OLN by the DEP S controller was premature.
2. The vectoring of VH-OJD onto right downwind for runway 16R by the APP S controller was initiated late.
3. The airspace agreement boundary for runway 16 operations restricted flexibility in the processing of both arrival and departure aircraft.

Factors

1. The radar surveillance techniques used by both controllers were inadequate to prevent the loss of the prescribed separation standards.

Safety action

As a result of occurrence 9503423, the Bureau of Air Safety Investigation made interim recommendation IR950212. As the interim recommendation is also applicable to this investigation, it is reproduced below.

IR950212

The Bureau of Air Safety Investigation recommends that Airservices Australia amend the runway 16 airspace agreement boundaries to ensure that arriving and departing aircraft cannot be on, or near, reciprocal tracks. The amendment should address excursions into either buffer area.

Circumstances

VH-OJJ was cleared to track inbound via the 229 VOR radial, while maintaining 6,000 ft. The Approach South radar control sector controller (APP S) was processing the aircraft for landing on runway 16R. Due to operational requirements, the APP S controller delayed turning the aircraft onto a right downwind for that runway.

VH-TCH had departed runway 16R, cleared initially to climb to 5,000 ft. The Departures South radar control sector controller (DEP S) cleared the aircraft for an early right turn and unrestricted climb to its planned cruising level. The aircraft was then to be vectored left to intercept the 207 VOR radial.

A short time later, as the APP S controller was about to instruct the crew of VH-OJJ to turn downwind and VH-TCH was turning left to intercept the 207 VOR radial, the crew of VH-OJJ advised that they had received a TCAS Resolution Advisory (RA) alert.

Recorded radar information indicated that each aircraft had penetrated its respective airspace boundary buffer, and closed to within 2.5 NM while both were at 6,000 ft.

The runway 16 airspace agreement has a narrow corridor in the APP S airspace to the west of the airport. This airspace design limits the flexibility available to APP S controllers when vectoring aircraft to downwind for runway 16. The latitude that the DEP S controller may apply when turning departing aircraft onto south-westerly tracks, and providing climb, is also restricted.

Separation was not ensured before VH-TCH was cleared for an unrestricted climb. The situation was possibly worsened by the southerly wind which would have drifted VH-TCH closer to the APP S airspace boundary.

Findings

1. The unrestricted climb instruction provided to VH-TCH by the DEP S controller was premature.
2. The vectoring of VH-OJJ onto downwind for runway 16 by the APP S controller was initiated late.
3. The airspace agreement boundary for runway 16 operations did not afford adequate separation assurance.

Factors

1. The radar surveillance techniques used by both controllers were inadequate to prevent the loss of the prescribed separation standards.

Safety action

As a result of the investigation, the Bureau of Air Safety Investigation made the following interim recommendation.

IR950212

The Bureau of Air Safety Investigation recommends that Airservices Australia amend the runway 16 airspace agreement boundaries to ensure that arriving and departing aircraft cannot be on, or near, reciprocal tracks. The amendment should address excursions into either buffer area.

Airservices Australia responded to this recommendation as follows:

"A Standard Instrument Departure (SID) has been developed for non-jet southern departures which will provide greater separation assurance and reduce controller workload. At this stage we expect the new SID to be included in DAP EAST Amendment List 52.

I should, however, point out that there remains a requirement for air traffic control to apply vertical separation between departing aircraft and arriving aircraft until the departing aircraft is clear of approach airspace. Vertical separation is applied at the clearance delivery phase of flight. Jet aircraft are required to maintain 5,000' and propeller driven aircraft are required to maintain 3,000'. The need for crossovers between arriving and departing aircraft within the Sydney TMA is unavoidable."

VH-EAA was processed into the Sydney Terminal Area by the Approach south radar control sector, and was tracking via the 094 VOR radial, on descent to 6,000 ft in visual conditions. At 9 DME, the flight crew, in response to a TCAS RA alert, climbed the aircraft approximately 300 ft. They did not advise ATC of the alert.

VH-NEK had departed runway 16L, on initial climb to 5,000 ft, and was being processed to depart the Sydney Terminal Area by the Departures south radar control sector. The aircraft was vectored onto a north-easterly track from a left turn after take-off.

Recorded radar information indicated that VH-EAA had continued descent to a pressure altitude of 5,700 ft and VH-NEK had climbed to a pressure altitude of 4,900 ft. When their flight paths crossed, VH-EAA was 800 ft above, and 1.86 NM to the right of VH-NEK.

The traffic management plan, techniques and procedures, for processing both aircraft were adequate to maintain prescribed separation standards and tolerances in accordance with the runway 16 airspace agreement. However, neither controller had recognised the incident, probably due to the short duration of the encounter, and the lack of advice from either flight crew.

Findings

1. The traffic management procedures adopted by the controllers for processing the aircraft were adequate.

2. VH-EAA descended below the assigned altitude.

3. In response to the TCAS RA alert, the flight crew returned the aircraft to the assigned altitude.

Significant factors

1. The required separation standard was infringed when the flight crew permitted VH-EAA to descend below their assigned altitude.

As VH-NJR was approaching Perth from the east APP (E) was responsible for initial radar vectoring. To improve aircraft handling APP (W) agreed that APP (E) would maintain vectoring after the aircraft crossed into APP (W)'s airspace. APP (W) also indicated that he would keep all his other traffic clear of VH-NJR.

The pilot of VH-MPZ was cleared to depart Jandakot’s runway 06 in a left turn with a climb to 2,000 ft. He read back his allocated transponder code as 4503 instead of 4502 and the error was not detected despite a request to repeat his read-back. VH-MPZ's clearance for a departure from Jandakot meant that separation between VH-NJR (initially cleared to descend to 2,500 ft) and VH-MPZ (cleared to climb to 2,000 ft) was not assured. APP (W) did not realise this error, nor did he coordinate VH-MPZ's departure with APP (E) and as a result APP (E) was not warned there might be a traffic conflict. APP (W) had placed VH-MPZ's flight strip in the bay between the two controllers and had intended drawing APP (E)'s attention to it. APP (E) was busy, and APP (W) decided to leave it until later. He was then distracted by communications with another aircraft and forgot about it.

When VH-MPZ departed Jandakot its transponder code was set at 4503. A code of 4502 had been programmed into the radar's computer; consequently, when the return appeared on both APP (W) and APP (E)'s screens it did not have a label indicating the aircraft's callsign. It appears both controllers initially assumed that the un-labled return was circuit traffic at Jandakot and paid little attention to it. VH-MPZ exited the Jandakot control zone at the same time as APP (E) was giving further directions to VH-NJR to turn right and continue on a visual descent. Because APP (E) had the quick-look facility selected on her radar she observed that the traffic, which was now heading towards VH-NJR, was at 2,000 ft and would be in conflict. She immediately turned VH-NJR further right and assigned the aircraft 2,500 ft.  This was to provide emergency separation of 500 ft between the aircraft. VH-NJR descended to 2,300 ft before returning to 2,500 ft.

Analysis

The factors leading to the occurrence started when APP (W) cleared the pilot of VH-MPZ to depart Jandakot at 2,000 ft on a track that would take the aircraft towards the flight path of VH-NJR which had been cleared to descend to 2,500 ft. The separation requirement were not assured by this instruction. APP (W) should have cleared VH-MPZ via a different route or restricted its climb to 1,500 ft. APP (W) could also have coordinated a descent limit of 3,000 ft for VH-NJR with APP (E), to provide the required assurance. A lack of commitment to the principal of separation assurance was identified as a possible factor in APP (W)'s under-performance.

Having started the process APP (W) did not ensure that APP (E) was aware of the possible traffic by drawing her attention to the flight progress strip located in the bay between the controllers. Distraction probably played a part in this failure. APP (E) was operating on the assumption that APP (W) was going to keep all other traffic clear and was not expecting any conflicting traffic and therefore, was not looking for it.

All the visual cues that may have been provided to both APP (W) and APP (E) by their radar screens were not there because VH-MPZ's pilot did not have the correct transponder code set. In addition, APP (W) did not have the quick-look facility selected and was therefore, not aware, at least, of the un-labled returns altitude. It was APP (E)'s use of the quick-look facility which alerted her to the approaching confliction. Use of the quick-look facility is not mandated because of the radar return clutter that results from the circuit traffic at Jandakot, when it is selected.

Safety Action

Airservices Australia's Western Australian office is reviewing the airspace layout around Perth and Jandakot, Jandakot departure procedures and coordination requirements, the use of the radar quick-look facility and methods of reducing radar clutter in the Jandakot area. They will also continue to emphasise, to their staff, the mandatory use of defensive control techniques that are designed to provide separation assurance in all appropriate circumstances.

At 1139 the Canberra approach controller cleared Hawk 02 to track to Canberra from the east-south-east at an altitude of 3,500 feet. Just after this VH-GJZ departed from runway 12, tracking via Bindook. The pilot had been told to turn left onto a heading of 070 degrees and climb to 4,500 feet. A short time later the approach controller passed the responsibility for Hawk 02 to Canberra tower, saying this aircraft was to track for a left base on runway 17. The pilot of Hawk 02 was given a visual approach and commenced descent.

At 1142 the pilot of VH-GJZ advised approach control he was climbing to 4500 feet and turning left onto a heading of 070 degrees. The approach controller realised that separation would be lost between VH-GJZ and Hawk 02. The controller told the pilot of VH-GJZ to stop the turn on a heading of 110 degrees. Horizontal separation reduced to about one mile before vertical separation was established. The pilot of VH-GJZ reported sighting Hawk 02 and was told to pass behind this aircraft, then turn left onto a heading of 040 degrees.

A third aircraft, callsign Squirrel 005, had been cleared direct to Canberra from the north-east at an altitude of 4500 feet. As a result of the controller's instructions to VH-GJZ this aircraft and Squirrel 005 were now on conflicting tracks. The pilot of Squirrel 005 was told to turn 30 degrees to the right and the pilot of VH-GJZ was told to climb to 7,000 feet. Horizontal separation between VH-GJZ and Squirrel 005 reduced below the minimum standard before vertical separation was established.

Significant Factors

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

1 The approach controller did not satisfactorily plan the handling of the sequence.

2 The approach controller did not take timely steps to avoid potential traffic conflicts.