United B773 at Sydney on Jan 22nd 2020, unexpected turn causes loss of separation
Last Update: July 28, 2020 / 10:50:10 GMT/Zulu time
About two minutes prior to the Boeing a Virgin Australia Avions de Transport Regional ATR-72-212A registration VH-FVQ performing flight VA-1153 from Sydney,NS to Tamworth,NS (Australia) had departed Sydney's runway 34R and was climbing through 1800 feet MSL at that time.
Due to the right turn by the Boeing the separation between the aircraft reduced, Departure Control intervened and sent the Boeing onto the left turn, which the crew initiated. Nonetheless, the separation reduced to about 0 feet vertical and 1.3nm horizontal before the flight pathes began to diverge again.
Both aircraft continued to their destinations without further incidents.
Australia's TSB rated the occurrence a serious incident and opened a short investigation. The TSB wrote: "During initial climb, the Boeing 777 turned right resulting in a loss of separation with the ATR-72 departing from the parallel runway."
On Jul 28th 2020 the ATSB released their final report concluding the probable causes of the serious incident were:
- The pilot flying incorrectly amended the flight management computer (FMC) for the cleared departure.
- The amended FMC setup was probably not effectively communicated to the crew or effectively cross-checked by the pilot monitoring or relief pilots.
Other factors increasing risk
- The pilot monitoring did not complete a full readback of the radar transition component of the pre-departure clearance, nor did the Sydney clearance delivery controller insist on a full readback.
- The Sydney departures controller observed UA870 turning right and towards VOZ1153 and quickly issued unambiguous and immediate instructions to both aircraft to rectify the situation and re-establish the required separation.
The ATSB summarized the sequence of events:
Sydney Airport was configured for parallel runway operations, including simultaneous independent departures. VOZ1153 departed from runway 34R, to an assigned heading of 350º, just prior to UA870 departing from runway 34L. UA870 was required to maintain runway heading (335º) until reaching 1,500 ft, at which point the aircraft was cleared to turn left and track towards Richmond, northwest of Sydney. However, UA870 climbed straight ahead through to about 2,100 ft and then the aircraft turned to the right about 45º from the required heading, resulting in a loss of separation with VOZ1153. At their closest point of approach, the two aircraft were separated by 1,843 m (about 1.0 NM) laterally and 60 m (about 200 ft) vertically.
Air traffic control detected the loss of separation and issued interventional instructions to both aircraft. The required separation was re-established and both flights continued without further incident.
The Boeing 777 crew consisted of a captain, who was pilot flying, and three first officers. One of the first officers was pilot monitoring, the two other occupied the observer seats.
The ATSB analysed:
Flight management computer - departure setup
The foreign captain was expecting to receive a clearance via the SYD1 standard instrument departure and had pre-programmed the FMC in anticipation of this and briefed the other crew accordingly. However, the pre-departure clearance provided by air traffic control was different (RIC5). This was likely due to the captain’s limited exposure to the varying Sydney-centric departure procedures (SYD1 versus RIC5). In addition, the clearance included the radar transition procedure, with which the captain was unfamiliar, due to the predominant use of procedural-based transitions in the United States. Anything non-standard in departures or arrivals can add additional complexity, but particularly for crew that have very limited experience with the location, such as ong-haul foreign crew. Air traffic controllers have an opportunity to take into account the likelihood of a crew’s familiarity with the airport when issuing clearances to foreign crew.
The clearance meant the FMC needed to be re-programmed for the RIC5 procedure. During this process, the PF removed the discontinuity that was automatically generated in the FMC flight path, that is, the waypoint sequence to the cleared oceanic route. This would have been appropriate for many procedural transitions but not for a radar transition. The predominance of procedural transitions in the United States likely meant that the PF was focussed on removing the discontinuity (gap) in the FMC coding.
In this case, the purpose of the discontinuity was to represent controller-issued vectors as the aircraft tracked beyond 12 NM northwest of Sydney. In effect, the aircraft was cleared to 12 NM.
From that point they were required to wait for a controller initiated radar vector to re-join their cleared oceanic route to San Francisco commencing at waypoint DIPSO (to the east). In removing the discontinuity, the aircraft was re-programmed to track directly to DIPSO after reaching the initial waypoint at 1,500 ft where the aircraft should have turned left (before they reached the 12 NM point). Ultimately, this resulted in a right turn and, therefore, the loss of separation.
Effective crew coordination is fundamentally dependent upon effective communication. In order for cockpit crew members to share a ‘mental model’, or common understanding of the nature of events relevant to the safety and efficiency of the flight, communication is critical.22 The operator’s procedures were clear and provided an established framework for the flight crew to communicate and coordinate their activities to ensure a safe and expeditious departure.
A number of opportunities existed not only for the PM, but also the crew positioned in the observers’ seats (in-flight relief pilots), to verify the FMC setup between the departure briefing and entering the runway prior to take-off. The operator’s procedures included a comprehensive process by which crew use different pages (information sources) within the FMC to ensure the departure clearance is reflected accurately by the computer coding (waypoint sequence).
The PM was not aware of the amendment to the radar transition (deletion of the route discontinuity), which indicated that the PF may not have clearly verbalised the change and/or ensured the PM heard and understood the change, in accordance with the operator’s procedures. By not clearly verbalising this misunderstanding or the amendments to the departure route setup, the PF did not provide an opportunity for the rest of the crew to contribute effectively.
However, there were further opportunities for the PM or relief pilots to discover this error. The PM verified the FMC set up, but only used the summary RTE page rather than the LEGS page with greater detail, and therefore the waypoint sequencing error was not detected. Further, in the departure review just before take-off, both the PF and the PM noticed the ‘no transition’ on the FMC RTE page, but no-one recognised this was not in accordance with the radar transition segment of the clearance.
Effective communications also includes with external sources such as air traffic control. Readbacks of clearances and instructions to crew in the aviation context serves two main purposes; acknowledgement of both the intent and content of the clearance, and to reinforce the message has been acknowledged and understood. In this case, the PM provided a truncated readback to ATC, which did not provide this assurance. The truncated readback was not challenged by the controller. As such, the controller did not have any assurance that the flight crew heard and understood that they were cleared for a radar transition. This increased the risk of errors to the FMC setup and could have led to further confusion during the initial climb.
This article is published under license from Avherald.com. © of text by Avherald.com.
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