Loss of separation

Safety summary

What happened

On 18 January 2012at 2125 Eastern Daylight-saving Time, there was a loss of separation (LOS) between an Airbus A320, registered 9V-TAZ, and an Airbus A340, registered A6-EHH, 907 km NW of Karratha, Western Australia. The aircraft were under the air traffic control of Airservices Australia. The A320 was southbound at FL 350 and the A340 was heading west and cleared to operate in a ‘block’ level, anywhere between FL 340 and FL 360. The aircraft were estimated to cross waypoint TANEM within 2 minutes of each other. The relevant separation standards were 1,000 ft vertical separation or 15 minutes lateral separation at the same position. Controller 1, who approved the block level clearance, did not detect the traffic confliction prior to handing over to controller 2. After a short break, controller 2 handed back to controller 1, and the confliction was detected by controller 2 during the handover. Compromised separation recovery techniques were applied to re-establish vertical separation.

What the ATSB found

The two controllers were experiencing a high workload due to a range of factors, including traffic levels, weather diversions and the airspace configuration, and controller 1 had limited opportunity to consolidate their training and skills before being rostered onto more complex sectors and situations. The ATSB found that Airservices’ processes for monitoring and managing controller workloads did not ensure that newly-endorsed controllers had sufficient skills and techniques to manage the high workload situations to which they were exposed. In addition, Airservices had limited formal guidance regarding how to determine appropriate consolidation periods for en route controllers on one sector before they were transitioned to commence training on another sector. Further safety issues were also identified relating to the application of block level clearances, and the continuing absence of an automated air traffic conflict detection system available for conflictions involving aircraft that were not subject to radar or ADS-B surveillance services.

What's been done as a result

Airservices reported that changes had been made to the configuration, training and rostering arrangements for the airspace sectors involved in the occurrence. The commissioning of a radar in northern West Australia had reportedly alleviated controller workload in two of the airspace sectors, with enhanced surveillance of the majority of aircraft operating in that airspace expected with the mandate of automatic dependant surveillance- broadcast (ADS-B) effective in December 2013. A working group had also been established to determine a suitable workload model to monitor and forecast controller workload on a sector by sector basis. In addition, the first stage of a flight plan conflict function had also been deployed in Brisbane Upper Airspace, with further roll out planned in Melbourne Centre in 2014. The ATSB is not satisfied that Airservices has adequately addressed the identified safety issues regarding formal guidance for consolidation periods for newly-endorsed controllers and the limited formal guidance to controllers and pilots regarding the conditions in which it was safe and appropriate to use block levels. As a result, the ATSB has made formal recommendations to Airservices.

Safety message

Ideally the best way of managing workload is to reduce the level of work demands and distractions. If the work demands cannot be reduced, then another option is to ensure the controllers have the experience, skills and techniques to effectively manage their task demands. Overall, high workload can have significant effects on a controller’s performance, and it needs to be monitored and managed using a systemic approach, particularly for less experienced controllers but also controllers who have recently received a new endorsement. The instances of other recent loss of separation occurrences involving high workloads and newly-endorsed controllers on other sector indicates that this problem was not restricted to the sectors involved in this occurrence.

At about 1500 Eastern Daylight-saving Time, on 17 December 2011, a Cessna 172R aircraft, registered VH-LWX (LWX), landed on runway 13L at Moorabbin Airport. On board were a student pilot and instructor. The student was the handling pilot, and the instructor was the pilot in command.

On vacating the runway, LWX was issued a clearance by air traffic services to taxi back to base via taxiway C, but to hold short of runway 13R. The pilot read back the requirement to hold short of runway 13R. The holding point on taxiway C was appropriately marked; however, LWX did not stop at the holding point, but continued across the runway, resulting in a runway incursion.

At the time of the incursion, a Cessna 172S, registered VH-EOR (EOR), with two persons on board, had just touched down to land on runway 13R. On seeing LWX cross the runway, the pilot of EOR applied full power, commenced a go-around, and passed overhead LWX. EOR subsequently completed a circuit and landed safely. There were no injuries or damage to either aircraft.

The pilot in command of LWX reported that he had been distracted by discussions with his student. The quick action by the pilot of EOR demonstrated the need for landing aircraft to keep a good lookout. The incident also highlights the need to avoid distractions when operating on or near an aerodrome.

On 9 December 2011 a S.O.C.A.T.A. Groupe Aerospatiale TBM 700 aircraft, registered VH-VSV (VSV) departed Bankstown airport, for a private flight to Merimbula, New South Wales. Onboard the aircraft was a pilot and one passenger.

The pilot was cleared to depart Bankstown control zone on a downwind departure from runway 11 left, however mistakenly conducted an upwind departure. The aircraft penetrated Sydney controlled airspace by 2.3 NM and came within 1.2 NM with no vertical separation of another aircraft on approach into Sydney Airport and a breakdown of separation occurred.

The controller at Bankstown tower then instructed the pilot of VSV to conduct a left turn and track back overhead Bankstown airport.

This incident highlights the importance of developing a technique to ensure a clearance is processed, understood and actioned correctly. It is also important to clarify a clearance if any ambiguity exists. Finally, pre-flight planning is essential to ensure safe flight. CASA has published a Visual Pilot Guide for Archerfield, Jandakot, Melbourne, Parafield and Sydney areas to provide detailed assistance for operating in these areas.

What happened

On 23 November 2011, a loss of separation occurred 6 km north of Cairns, Queensland, between a Cessna Aircraft Company 402C (C402), registered VH-TFK, and a Cessna Aircraft Company T210N (C210), registered VH-PDP.

The C402 was conducting an instrument landing system (ILS) approach for runway 15 and was 1.8 NM (3.3 km) from the airport when the pilot initiated a missed approach from a height of 1,000 ft in instrument meteorological conditions. At the time the C210 was on the same ILS approach and was 6.4 NM (11.9 km) behind the C402. About 1 minute after the pilot of the C402 turned left to establish the aircraft on the missed approach track, the distance between the two aircraft reduced below the required air traffic control separation (ATC) standard.

What the ATSB found

The Australian Transport Safety Bureau identified that a local ATC procedure, published in part to assist ATC in separation management during a missed approach event, was not clear and subject to varying interpretation. This resulted in the spacing between the two aircraft being closer than intended at the point when the pilot of the C402 commenced the missed approach.

The local ATC procedure did not fully consider all operational aspects that may lead a pilot to initiate a missed approach in instrument meteorological conditions above the procedure-defined minimum cloud base height.

What has been done as a result

In response to this occurrence, Airservices has initiated a number of safety actions including amending the local procedure to assist with the clarity and intent, changing the Cairns local instructions to enforce minimum flow (distance) spacing and updating controller missed approach procedures refresher training. This updated training will increase controller awareness of separation assurance issues relating to consecutive approaches and ensure that due consideration is given by controllers to the broad mix of aircraft types using straight-in approaches.

Safety message

This occurrence reinforces the need for all local procedures, in particular those that assist controllers in separation management, to be unambiguous and to encompass all possible operational circumstances. The importance of effective radar navigation guidance when positioning an aircraft for an approach is also highlighted.

What happened

On 8 November 2011, a loss of separation occurred between a Boeing Company 737-8FE, registered VH-VUV, and a Boeing Company 737-838, registered VH-VXM, near Ceduna, South Australia. The aircraft were conducting scheduled passenger flights and were under the air traffic control of Airservices Australia (Airservices). The aircraft were operating on converging tracks at 39,000 ft. The procedural longitudinal separation standard of 20 NM (37 km) was infringed. It is likely that there was between 6 NM (11.1 km) and 12 NM (22.2 km) longitudinal separation between the aircraft.

What the ATSB found

The ATSB found that the two controllers involved were experiencing a high workload due to a range of factors, including the number of tasks and their limited experience. Airservices’ processes for monitoring and managing controller workloads did not ensure that newly-endorsed controllers had sufficient skills and techniques to manage the high workload situations to which they were exposed. In addition, Airservices’s fatigue risk management system (FRMS) did not effectively manage the fatigue risk associated with allocating additional duty periods. The ATSB is also concerned that there had been increasing traffic levels and complexity in some sectors in recent years, combined with a decrease in the experience levels of controllers and without a concomitant increase in controller resources. In addition, although Airservices has been in the process of developing and trialling a flight plan conflict function for procedurally-controlled aircraft for several years, the fact that it is still not operational is a safety issue.

What's been done as a result

Airservices reported that the airspace sectors involved in the occurrence had been re-sectorised into three sectors in November 2012 to manage workload and that a working group had been established to determine a suitable workload model to monitor and forecast controller workload on a sector by sector basis. The first stage of a flight plan conflict function had also been deployed in Brisbane Upper Airspace, with further roll out planned in Melbourne Centre in 2014.
In addition, Airservices reported that an updated FRMS had been implemented in July 2012 and that it had addressed the systems limitations outlined in the report.

Safety message

High workload can have significant effects on a controller’s performance. It needs to be monitored and managed using a systemic approach, particularly for less experienced controllers but also those who have recently received a new endorsement. Other recent loss of separation occurrences involving high workloads and newly-endorsed controllers indicate that this problem is not restricted to the sectors involved in this occurrence. Ideally the best way of managing workload is to reduce the level of work demands and distractions. If the work demands cannot be reduced, then another option is to ensure the controllers have the experience, skills techniques and support to effectively manage their task demands.

At 1500:51 Eastern Daylight-saving Time on 8 October 2011, a breakdown of separation (BOS) occurred 59 km north-east of Armidale, New South Wales between a Boeing Company 737-8FE (737), registered VH-YVA, and a Gulfstream Aerospace Corporation Gulfstream IV (G-IV), registered VH-CGF.

Both aircraft were under radar surveillance and subject to an air traffic control (ATC) service. The aircraft were on reciprocal tracks on air routes that intersected about 35 NM (65 km) north-east of Armidale.

The Australian Transport Safety Bureau (ATSB) established that the controller's mental model for separation correctly identified the situation and included a plan to manage the traffic. However, the instructions that were issued to the pilot of the G-IV contradicted that mental model in that the controller cleared the G-IV for descent through and below the level being maintained by the 737. The progression towards the BOS continued when the controller did not recognise the error during the G-IV pilot's read-back of the clearance.

Ultimately, the controller's earlier correct level input into The Australian Advanced Air Traffic System allowed a system alerting function to activate. In response to that alert, the controller initiated compromised separation recovery actions to recover the required separation standard.

The ATSB identified a number of human factors and individual work processes that contributed to the occurrence. In addition, a safety issue was identified in respect of differences in the traffic alert phraseology between the Manual of Air Traffic Services and Aeronautical Information Publication (AIP). These differences increased the risk of non-standard advice being provided to pilots by controllers during compromised separation recoveries.

In response to this safety issue, Airservices Australia (Airservices) amended the AIP to enhance understanding of the criticality of any safety alerts and avoiding actions being provided to flight crew. This amendment came into effect on 28 June 12.

Section 21 (2) of the Transport Safety Investigation Act 2003 (TSI Act) empowers the Australian Transport Safety Bureau (ATSB) to discontinue an investigation into a transport safety matter at any time. Section 21 (3) of the TSI Act requires the ATSB to publish a statement setting out the reasons for discontinuing an investigation.

On 12 October 2011, the ATSB commenced an investigation into the breakdown of separation, between an Airbus Industrie A320 aircraft registered VH-VGR and a Boeing Company 737 aircraft registered VH-VOD near Melbourne Airport, Vic. Examination of the information collected during the investigation identified that the occurrence had significant similarities to aspects of ongoing investigation AO-2010-104, breakdown of separation, between a Boeing Company 767 aircraft registered VH-OGU and a Boeing Company 737 aircraft registered VH-VBH, near Melbourne Airport, Vic on 5 December 2010.

Accordingly, the ATSB decided to examine the 12 October 2011, breakdown of separation event as part of the broader investigation AO-2010-104 and the separate AO-2011-131 investigation was discontinued.

On 26 September 2011 at 1151 Eastern Standard Time, the crew of an Airbus A321 (Airbus) aircraft, registered VH-VWW, received on the aircraft's traffic alert and collision avoidance system (TCAS) a traffic advisory (TA) alert, for an aircraft that was approaching from their front-right position at 2 NM (3.7 km) at 2,700 ft. The Airbus was maintaining 3,000 ft on an ARBEY standard terminal arrival route to runway 34 Left at Melbourne Airport, Victoria and was in Class C controlled airspace. The upper limit of non-controlled Class G airspace in the area was 2,500 ft.

It was later found that the pilot of the other aircraft a Piper PA-28-181 Archer, registered VH-TXD, had incorrectly set the aircraft's altimeter barometric pressure subscale setting, resulting in the aircraft entering controlled airspace without a clearance and a violation of controlled airspace occurring.

The occurrence was quickly resolved due to the traffic alert from the Airbus A321 aircraft's TCAS and the subsequent response from the flight crew.

This incident acts as a reminder to pilots of the importance to cross-check cockpit settings before flight.

On 12 August 2010, at about 1402 Eastern Standard Time, the pilot of a Piper PA-28-161 (Warrior II) aircraft registered VH-BZE (BZE) was cleared by the Surface Movement Controller (SMC) to taxi to holding point Alpha 2 (A2) for a departure from runway 13R, on a private navigational flight from Moorabbin Airport, Victoria. Following line up checks, the pilot was issued a takeoff clearance for runway 13R. Another aircraft, VH-PVL, that had recently landed on runway 13R was cleared to cross runways 22, 17L and 17R during taxi. The pilot of BZE inadvertently began a take-off roll on runway 17R instead of runway 13R, which resulted in a runway incursion. The aircraft came within 100 m of each other before BZE exited at the first taxiway and returned to the apron. There were no injuries to the occupants and nil damage to either aircraft.

The pilot of BZE became disorientated at holding point A2 as it was a combined entry to both runway 13R and 17R. Information regarding potential runway conflict areas (hotspots) was available for the airport on the Airservices Australia (Airservices) website, but this was not common knowledge to all airport users.

On 7 August 2011, a Cessna Aircraft 172, registered VH-WYG (WYG), departed Bankstown, New South Wales, for a student solo-navigation exercise. WYG entered Sydney controlled airspace without a clearance, which subsequently resulted in a breakdown of separation with a departing Boeing 747 aircraft, registered N171UA. Air Traffic Services (ATS) alerted the crew of N171UA to the traffic, and issued instructions for N171UA to conduct an avoidance turn away from WYG.

When the pilot of WYG contacted ATS for an airways clearance to conduct the Sydney Harbour scenic route, he was informed that he had been radar-identified as having entered controlled airspace without a clearance. The pilot then remained outside controlled airspace and subsequently elected to terminate the navigation exercise and return to Bankstown via the Lane of Entry.

The pilot reported that inclement weather had influenced his en-route track decision making during the flight.

This incident highlights the importance of both weather avoidance, and awareness of proximity to controlled airspace.