A Virgin Australia Boeing 737-800, registration VH-YIL performing flight VA-920 from Brisbane,QL to Sydney,NS (Australia), was on final visual approach to Sydney's runway 34L when the aircraft descended through 1000 feet AGL with speedbrakes not armed and the final flap setting had not yet been set. Descending through 875 feet AGL the flaps were set, at 500 feet AGL the commander spotted the speed brakes not set and armed them. The aircraft continued for a safe landing.
The Australian ATSB released ther final report concluding the probable causes of the incident were:
After air traffic control provided clearance for the crew to conduct a visual approach, a required autopilot altitude selection was not completed. As a result, the aircraft later deviated above the desired approach path.
- While re-establishing the approach path, the crew did not complete required landing procedures until after the aircraft descended below the stabilisation criteria check altitude. Subsequently the flight crew did not perform the required missed approach, instead continuing the approach and landing.
The ATSB analysed:
As the aircraft descended towards Sydney, the crew were provided with a visual approach clearance which the captain reported was unusual. After receiving the clearance, the captain unintentionally did not make the required 500 ft selection in the altitude window of the mode control panel. The first officer, as the pilot monitoring, did not identify that this omission had occurred. Consequently, as the aircraft descended to 2,000 ft the autopilot began to level off rather than continuing the descent to 500 ft, which took the aircraft above the desired descent profile. The captain responded with an unplanned manual intervention without alerting the first officer to their intention while the flight crew were also attempting to complete the final landing procedures. This led to an unexpected increase in flight crew workload and reduced the first officers situation awareness.
Workload has been defined as reflecting the interaction between a specific individual and the demands imposed by a particular task. Workload represents the cost incurred by the human operator in achieving a particular level of performance (Orlady and Orlady, 1999). A discussion of the effect of workload on the completion of a task requires an understanding of an individuals strategies for managing tasks.
An individual has a finite set of mental resources they can assign to a set of tasks (for example, performing an approach and landing). These resources can change given the individuals experience and training and the level of stress being experienced at the time. An individual will seek to perform at an optimum workload by balancing the demands of their tasks. When workload is low, the individual will seek to take on tasks. When workload becomes excessive the individual must, as a result of their finite mental resources, shed tasks.
An individual can shed tasks in an efficient manner by eliminating performance on low priority tasks. Alternatively, they can shed tasks in an inefficient fashion by abandoning tasks that should be performed. Tasks make demands on an individuals resources through the mental and physical requirements of the task, temporal demands and the wish to achieve performance goals (Hart and Staveland, 1988, and Lee and Liu, 2003).
In this case, likely in response to increased workload and the absence of crew coordination, they missed required checklist items (the final flap and speed brake selections). The stabilised approach criteria required that the aircraft be in the final landing configuration by 1,000 ft above the airport elevation. The landing flap selection was made 3 seconds after descending below this height, although the captain believed that the flap selection had been made in time to meet the stabilised approach criteria requirements. However, the flaps did not reach the required position until the aircraft descended through 875 ft above the airport elevation.
The first officer identified that the flap selection was made late and that, therefore, the stabilised approach criteria had not been met. However, as the descent rate, speed and profile were within the criteria, they announced that the approach was stable instead of making the required not stable announcement. Consequently, the required missed approach was not commenced, and the approach was continued. The first officer did not identify that the speed brake landing procedure action was not completed.
As the approach continued, the descent rate exceeded the stabilised approach criteria for a period of 9 seconds. This exceedance was momentary and not excessive and therefore it did not require the commencement of a missed approach.
When the unarmed speed brake was later identified by the captain, this should have acted as a further trigger for the commencement of a missed approach. Instead, this missed action was quickly rectified by the captain and the approach continued.
The Australian ATSB released ther final report concluding the probable causes of the incident were:
After air traffic control provided clearance for the crew to conduct a visual approach, a required autopilot altitude selection was not completed. As a result, the aircraft later deviated above the desired approach path.
- While re-establishing the approach path, the crew did not complete required landing procedures until after the aircraft descended below the stabilisation criteria check altitude. Subsequently the flight crew did not perform the required missed approach, instead continuing the approach and landing.
The ATSB analysed:
As the aircraft descended towards Sydney, the crew were provided with a visual approach clearance which the captain reported was unusual. After receiving the clearance, the captain unintentionally did not make the required 500 ft selection in the altitude window of the mode control panel. The first officer, as the pilot monitoring, did not identify that this omission had occurred. Consequently, as the aircraft descended to 2,000 ft the autopilot began to level off rather than continuing the descent to 500 ft, which took the aircraft above the desired descent profile. The captain responded with an unplanned manual intervention without alerting the first officer to their intention while the flight crew were also attempting to complete the final landing procedures. This led to an unexpected increase in flight crew workload and reduced the first officers situation awareness.
Workload has been defined as reflecting the interaction between a specific individual and the demands imposed by a particular task. Workload represents the cost incurred by the human operator in achieving a particular level of performance (Orlady and Orlady, 1999). A discussion of the effect of workload on the completion of a task requires an understanding of an individuals strategies for managing tasks.
An individual has a finite set of mental resources they can assign to a set of tasks (for example, performing an approach and landing). These resources can change given the individuals experience and training and the level of stress being experienced at the time. An individual will seek to perform at an optimum workload by balancing the demands of their tasks. When workload is low, the individual will seek to take on tasks. When workload becomes excessive the individual must, as a result of their finite mental resources, shed tasks.
An individual can shed tasks in an efficient manner by eliminating performance on low priority tasks. Alternatively, they can shed tasks in an inefficient fashion by abandoning tasks that should be performed. Tasks make demands on an individuals resources through the mental and physical requirements of the task, temporal demands and the wish to achieve performance goals (Hart and Staveland, 1988, and Lee and Liu, 2003).
In this case, likely in response to increased workload and the absence of crew coordination, they missed required checklist items (the final flap and speed brake selections). The stabilised approach criteria required that the aircraft be in the final landing configuration by 1,000 ft above the airport elevation. The landing flap selection was made 3 seconds after descending below this height, although the captain believed that the flap selection had been made in time to meet the stabilised approach criteria requirements. However, the flaps did not reach the required position until the aircraft descended through 875 ft above the airport elevation.
The first officer identified that the flap selection was made late and that, therefore, the stabilised approach criteria had not been met. However, as the descent rate, speed and profile were within the criteria, they announced that the approach was stable instead of making the required not stable announcement. Consequently, the required missed approach was not commenced, and the approach was continued. The first officer did not identify that the speed brake landing procedure action was not completed.
As the approach continued, the descent rate exceeded the stabilised approach criteria for a period of 9 seconds. This exceedance was momentary and not excessive and therefore it did not require the commencement of a missed approach.
When the unarmed speed brake was later identified by the captain, this should have acted as a further trigger for the commencement of a missed approach. Instead, this missed action was quickly rectified by the captain and the approach continued.
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