Qantas B738 and Qantas A332 at Sydney on Aug 5th 2019, loss of separation

Last Update: October 12, 2023 / 10:27:15 GMT/Zulu time

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Photo of Qantas VH-EBJ, Boeing 737-800 — Qantas VH-EBJ, Boeing 737-800 (Photo credit: simonmgc / Flickr / License: CC by-nd)

Incident Facts

Date of incident
Aug 5, 2019

Classification
Incident

Cause
Loss of separation

Airline
Qantas

Flight number
QF-459

Departure
Sydney, Australia

Destination
Melbourne, Australia

Aircraft Registration
VH-EBJ

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

Airport
Sydney Kingsford Smith International Airport, Sydney

Airport ICAO Code
YSSY

A Qantas Airbus A330-200, registration VH-EBJ performing flight QF-459 from Sydney,NS to Melbourne,VI (Australia), was lined up on Sydney's runway 34R and waiting for departure.

A Qantas Boeing 737-800, registration VH-VZO performing flight QF-545 from Brisbane,QL to Sydney,NS (Australia), was on final approach to runway 34R.

After the preceding landing had vacated the runway, tower cleared QF-459 for immediate takeoff, the aircraft commenced takeoff along their planned and assigned standard departure route.

However, the separation between the departure and approach became too tight, tower instructed QF-545 to go around from low height and further instructed the aircraft to turn onto an easterly heading. This heading however conflicted with the departure route of QF-459, a loss of separation occurred and the departing A330 received a TCAS traffic advisory. The departing A330 climbed above the Boeing joining a right downwind, which resolved the conflict.

The Boeing 737 landed safely on runway 34R about 10 minutes after the go around. The Airbus continued to Melbourne for a safe landing without further incident.

Australia's ATSB reported the occurrence was rated a serious incident (but did not report the minimum separation between the aircraft) and opened an investigation estimated to complete in 2nd quarter of 2020.

On Jan 16th 2020 the ATSB reported the minimum separation between the two aircraft reduced to 500 feet vertical and 0.43nm horizontally.

At the time a student controller under supervision by a training instructor was working the tower position. The ATSB characterized the student controller: "The ADC-E trainee was an experienced controller. He had previously worked as an ADC in another tower and had a surface movement controller rating at Sydney. At the time of the occurrence, he had neared the end of his training for the Sydney ADC-E position, with his performance check to obtain his rating scheduled for the next day. Both the ADC-E and OJTI (On the Job Training Instructor) had completed compromised separation recovery training."

The ATSB detailed the sequence of events: "The ADC-E controller reported that he had both aircraft in sight. In an attempt to increase separation between the two aircraft, he instructed the 737 flight crew to turn further right. The 737 was then at about 980 ft, which was below the minimum vectoring altitude (at night). As both aircraft converged, the A330 flight crew received a traffic advisory alert from their aircraft’s airborne collision avoidance system (ACAS). The A330 first officer, who was pilot flying,[2] then saw the 737 in close proximity and, in response, reduced the aircraft’s angle of bank to reduce the turn towards the 737. The captain of the A330 made a radio transmission to advise the ADC-E controller that it was ‘very close’. The controller then issued an instruction to the A330 flight crew to turn left. The A330 climbed to 5,000 ft and continued to Melbourne without further incident. The 737 climbed to 3,000 ft and was issued radar vectors for a second approach to runway 34R. It landed without further incident a short time later."

The ATSB reported they are reviewing the standard departure and approach procedures with respect to go around procedures. The ATSB stated: "As in this occurrence, should an aircraft be departing on the MARUB 6 SID at the same time an aircraft conducts a go-around from runway 34R, both aircraft will track out to the east. There is potential that those flight paths will conflict and require intervention from ATC in order to ensure separation is maintained between the aircraft."

On Oct 12th 2023 the ATSB released their final report concluding the probable causes of the incident were (emphasis by ATSB):

Contributing factors

- The 737 flight crew did not maintain the aircraft’s speed within the specified range during the first part of final approach, and did not advise air traffic control of this non-compliance as required by the approach procedure.

- The spacing between the landing Dash 8 and the following 737 on approach reduced to less than 5 NM without the required coordination between the approach controller and aerodrome controller position prior to transfer.

- The trainee aerodrome controller’s judgement of the spacing between the Dash 8 and 737 was likely affected by incomplete appreciation of their initial spacing and speed difference. As a result, the A330 was instructed to line up and was then issued a clearance for an immediate take‑off without sufficient spacing to prevent a runway separation issue or go-around. Because the respective departure and missed approach procedures both involved climbing from a low level and tracking to the east, this led to a compromised separation situation.

- After initiating the missed approach, the 737 flight crew inadvertently continued on the runway heading above the mandatory 600 ft turn beyond the missed approach point, and did not turn until instructed by the trainee aerodrome controller. As a consequence, the flight path of the 737 was closer to that of the A330’s departure track than it would have been if the turn had been commenced at the required height.

- Although the trainee aerodrome controller’s instruction for the 737 to initiate the turn reduced the collision risk, the extension of the turn to 100° did not mitigate the short-term effect of the delayed and relatively large-radius turn of the 737, or modify the A330’s projected flight path. Further, the aerodrome controller did not issue the 737’s turn instruction using the phrase required for avoiding action or issue a safety alert to either flight crew.

- After the missed approach was initiated, the on-the-job training instructor’s prompts to the trainee aerodrome controller were at the lower level of the prompting hierarchy and did not reflect the potential criticality of the situation or elicit an effective response.

- The Airservices Australia MARUB SIX standard instrument departure and the missed approach procedure for runway 34R directed aircraft onto outbound tracks that did not sufficiently assure separation between aircraft following the procedures concurrently. (Safety issue)

- Although Airservices Australia applied operational risk assessments to high-level threats, it did not formally assess and manage the risk of specific threat scenarios. As a likely result, Airservices did not formally identify and risk manage the threat of separate aircraft concurrently carrying out the MARUB SIX standard instrument departure and a missed approach from runway 34R at Sydney Airport, even though it had been a known issue among controllers generally. (Safety issue)

Other factors that increased risk

- The tower shift manager (TSM) was fully engaged in a controller function and was not aware of the missed approach and development of the compromised separation until after the event. This negated the TSM role as a risk control and increased the risk that a compromised separation would not be managed effectively.

- The missed approach points pre-programmed into the flight management computer of Qantas 737s were incorrect for 8 different approaches to Sydney runway 34R. The missed approach points were located over the runway threshold, which was not consistent with the locations of the missed approach points as determined by the relevant instrument approach charts.

- Airservices Australia did not have procedural controls to separate aircraft concurrently carrying out the MARUB SIX standard instrument departure and a missed approach from runway 34R at Sydney Airport while below the minimum vector altitude at night. (Safety issue)

- Airservices Australia’s compromised separation recovery training for Sydney tower controllers did not include scenarios involving aircraft below the minimum vector altitude at night. (Safety issue)

- After the occurrence, the trainee aerodrome controller transferred the 737 to the approach controller without the separation standard being met and without coordination.

The ATSB reported Airservices Australia (ATC provider) did a re-design of the missed approach and departure procedures effective Dec 2021 to reduce the likelihood of a re-occurrence.

Keypoints of the ATSB analysis:

On the night of 5 August 2019, aircraft landing and taking off from runway 34R were controlled from the Sydney air traffic control (ATC) tower via the ‘aerodrome controller (ADC) – east’ position. That position was operated by a trainee ADC and an on-the-job supervisor.

Following the landing of a Dash 8, the trainee ADC cleared the Airbus A330 to line up and take off while the Boeing 737 was on final approach to land. After realising that runway separation could not be assured, the trainee controller instructed the 737 to go around (conduct a missed approach). During the subsequent missed approach and turn to the right, the 737 came into close proximity with the A330 on its initial climb and turn to the right. This was classified as a ‘loss of separation’ under the ATSB’s occurrence classification system.

The loss of separation and close proximity between the 737 and the A330 was the culmination of a series of events that, individually, would only be minor concerns but collectively resulted in a serious incident.

...

In the initial parts of the approach the 737 flight crew operated at higher speeds than specified for the IVA. The aircraft was well above the maximum speed when 10 NM from the threshold and did not attain the required speed until after the trainee aerodrome controller (ADC) instructed the A330 crew to line up.

Although this did not have any detrimental effect on the 737’s operation (as the approach was stable), it contributed to the reduction of spacing between the 737 and the preceding Dash 8 and gave the trainee ADC less time to process the A330 departure. The flight crew did not advise air traffic control (ATC) of this increased speed, as required by the approach chart, and this probably affected the trainee ADC’s judgement of the amount of time available before the 737 would cross the runway threshold, as detailed in the following section.

...

The local instructions applicable at the time specified the minimum distance between successive arrivals to runway 34R to be 5 NM. This distance could be reduced in some cases (not below 3 NM) if there was prior coordination between the approach and aerodrome controllers.

In this case, the spacing between the landing Dash 8 and the following 737 on approach was 4.5 NM when the 737 was instructed to contact the tower (ADC), and 4.1 NM when the ADC was first contacted. However, the approach controller had not coordinated with the trainee ADC for the transfer as required by the Sydney operational procedures.

...

The trainee ADC and OJTI both reported being aware that the spacing between the arriving Dash 8 and following 737 aircraft was less than the specified minimum of 5 NM by the time the Dash 8 crossed the threshold. However, the trainee ADC must have still anticipated that there was a sufficient gap at this time to allow the A330 to depart. It is likely that, having formulated a plan to allow the A330 to take-off between the Dash 8 and 737, and in the absence of knowledge about the 737 not maintaining the specified speed, the gradual reduction in spacing as the Dash 8 approached had not been enough of a prompt for the trainee ADC to challenge their commitment to the plan.

To execute the plan, the trainee ADC expedited the departure of the A330 by lining it up to hold on the runway so the crew was ready to start the take-off roll as soon as the Dash 8 was clear of the runway. The trainee ADC did not consult with the OJTI before initiating the A330 departure and there was no obligation to do so.

In any case, once the Dash 8 was clear of the runway the trainee ADC issued a clearance to the A330 for an immediate take-off, and the crew complied.

As the A330 started to roll the trainee ADC’s attention turned to the 737 on final approach, and the OJTI asked whether the runway separation standard would be met. The trainee ADC correctly assessed that the A330 might not be clear before the 737 passed over the threshold, so instructed the 737 crew to go around (conduct a missed approach) to avoid a runway loss of separation.

...

When instructed to go around (conduct a missed approach), the 737 crew was required to fly to the missed approach point and then follow the missed approach procedure for the runway 34R GLS approach unless otherwise advised by ATC. As specified on the approach chart, this was an initial track of 335° (runway bearing), then a mandatory right turn at 600 ft onto a 070° track, and climb to 2,000 ft.

As the aircraft would already be climbing before it reached the missed approach point, it would be expected that the aircraft would be above 600 ft at or soon after the missed approach point and then commence the turn. In this occurrence, however, the flight crew did not commence the turn until after this when at 1,100 ft, after they were instructed by the trainee ADC.

The 737 flight crew had an early awareness that separation from the rolling A330 would be marginal and they initiated the missed approach without delay. The initial actions were performed correctly. The crew had briefed the procedure for Sydney, which required the turn to be initiated after the landing gear and initial flap retraction, and for further flap retraction to be delayed.

However, the first officer (FO) as pilot flying (PF) inadvertently followed the trained procedure for missed approaches (which was applicable to airports other than Sydney and did not involve an early turn). There were several contextual factors that likely contributed to this relatively late turn.

Missed approaches generally result in a high flight crew workload, particularly when they are manually flown like this one. Research has found that during missed approaches, there is an increase in the number of flight crew errors including flight path deviations (Dehais and others, 2017). Aspects of this missed approach that increased crew workload included a level-off altitude that was lower than typical, and the need for a turn soon after passing the missed approach point.

This was about 12 seconds after clearing the A330 for take-off. At this point, the 737 was 1.2 NM (2.2 km) from the threshold and the A330 was rolling and accelerating through 60 kt. The trainee ADC had the option to instruct the A330 crew to reject the take-off but (reasonably) wanted to avoid the risks associated with rejected take-offs.

...

Throughout the missed approach sequence, the trainee ADC was applying visual separation. In the first phase of the missed approach, the 737 was travelling in the general direction of the tower, and it was after last light, which probably affected both controllers’ ability to visually determine the position of the 737 from the tower.

Another contextual factor was the historical variability in the location of the height-based right turn in the first part of the missed approach (Figure 15 and discussed further in Missed approach and departure procedures). This meant that the tower controllers could not develop a consistent visual reference to aid in their assessment of aircraft conformance to the runway 34R missed approach procedure (since other aircraft they saw likely turned at differing points).

In summary, it may not have been obvious at first that the 737 flight path was not conforming to the missed approach procedure.

From recent discussion of the scenario of an aircraft taking off concurrently with an aircraft going around from runway 34R, the trainee ADC was aware of the potential for compromised separation. The trainee ADC was also aware that an intervention might be required to preserve separation and that vectoring was not permitted at night below the MVA. Instead, the trainee ADC appropriately applied ‘best judgement and initiative’, which allowed controllers to work outside of prescribed actions when the safety of an aircraft may be considered to be in doubt, as in this case.

Observing that the 737 was not turning, the trainee ADC instructed the 737 crew to turn right onto a heading of 100°. This was about 9 seconds after the 737 passed through the 600 ft mandatory turn height, as described in 737 flight path during missed approach. By turning the 737 further than the default 070°, the trainee ADC was intending to direct the 737 onto a flight path that was divergent to the A330 in the process of turning to intercept the 075° radial.

The trainee ADC’s instruction to the 737 to turn, soon after the aircraft passed 600 ft, was an important factor in keeping the two aircraft apart. However, in the absence of any other intervention, the instruction to turn would not prevent separation from being compromised. As the turn progressed, the 737 flight path was further to the north than the trainee ADC had anticipated due in part to the radius of turn (as a result of the 737’s increased speed since passing the missed approach point). The instruction to turn to heading 100° instead of the 070° specified by the procedure had no effect in the early part of the turn that was critical to separation.

Further, the trainee ADC did not issue the 737’s turn instruction using the phrase required for avoiding action, which would have alerted the 737 flight crew of the potential traffic conflict with the A330 and emphasised the reason for the instruction. As a result, their immediate response was not assured and the turn was not made at the fastest possible rate. ATSB analysis indicated that a maximum-rate turn probably would have increased the minimum distance between the aircraft to about 0.55 NM (1.0 km). The trainee ADC also did not issue either flight crew with a safety alert to advise of the unsafe proximity situation.

...

The trainee ADC was operating under the supervision of a qualified on-the-job training instructor (OJTI) who was responsible for the safety and efficiency of the aerodrome control function for runway 34R. Although the OJTI had the authority to override the trainee ADC, any intervention would have resulted in deferral of the check planned for the next day. In addition, and based on the trainee ADC’s recent performance, the OJTI was expecting the trainee ADC to identify and manage traffic conflicts with minimal prompting and no intervention. The trainee ADC had been operating with similar expectations.

When the trainee ADC instructed the A330 crew to line-up then cleared them for an immediate take-off, the OJTI considered the sequencing of the A330 departure was ‘ambitious’ but this was not communicated to the trainee at the time because there was a possibility the plan could work, and would be an opportunity for the trainee ADC to demonstrate a solution. Once the trainee ADC instructed the 737 crew to conduct a missed approach, the OJTI was aware that the aircraft would need to be separated and prompted the trainee ADC to focus on a resolution.

The OJTI reported they would have preferred the trainee ADC to cancel the SID and provide the A330 flight crew with a heading to the right of the runway centreline (such as 030°) to resolve the compromised separation, but did not communicate this to the trainee. As described above, the trainee instructed the 737 crew to turn right to heading 100°. The OJTI recalled understanding the trainee’s logic for the instructions, but would not have chosen this strategy to resolve the situation and believed more azimuth could have been provided to the 737.

There were differing understandings between the trainee ADC and OJTI in managing the compromised separation situation. Communications effectiveness depends on shared assumptions, a shared mental model or shared situation awareness (Salas and others 1995).

...

In this case, after the A330 was cleared for take-off, the OJTI asked the trainee ADC whether the runway separation standard would be met. This successfully prompted the trainee ADC to reassess the spacing between the two aircraft and led to the instruction for the 737 to go around. The OJTI then prompted the trainee ADC to resolve the separation issue by directing the trainee’s attention to resolving the situation, asking ‘what are we going to do’ and to provide the aircraft with more horizontal separation. From this communication, the trainee ADC likely believed they shared the same understanding of the situation and had chosen the same solution, or at least a feasible one.

However, the OJTI did not use the higher levels to communicate to the trainee ADC the urgency of the situation, did not prompt the trainee ADC to share their mental model of the emerging traffic picture or confirm that the trainee ADC was projecting the flight paths accurately. This also meant that the trainee ADC may not have had sufficient prompts to question their interpretation of the developing situation. It is likely the OJTI was cognisant that the trainee ADC needed to demonstrate competence without intervention, and was reluctant to provide additional instructions to manage and recover from the compromised separation situation effectively.

Metars:
YSSY 051130Z 34001KT CAVOK 14/12 Q1022 NOSIG=
YSSY 051100Z 00000KT CAVOK 14/12 Q1022 NOSIG=
YSSY 051030Z 00000KT CAVOK 15/11 Q1022 NOSIG=
YSSY 051000Z 05004KT CAVOK 16/12 Q1022 NOSIG=
YSSY 050930Z 02006KT CAVOK 17/13 Q1021 NOSIG=
YSSY 050900Z 04007KT CAVOK 17/13 Q1021 NOSIG=
YSSY 050830Z 04008KT CAVOK 17/13 Q1021 NOSIG=
YSSY 050800Z 04009KT CAVOK 17/13 Q1021 NOSIG=
YSSY 050730Z 05009KT CAVOK 17/13 Q1021 NOSIG=
YSSY 050700Z 05011KT CAVOK 18/12 Q1021 NOSIG=
YSSY 050630Z 04013KT CAVOK 19/12 Q1021 NOSIG=
YSSY 050600Z 05012KT CAVOK 19/12 Q1021 NOSIG=