Incident Overview
An aircraft on descent towards Sydney experienced a breakdown in crew coordination and task management during a visual approach. The captain described the visual approach clearance as unusual. After receiving the clearance, the captain inadvertently omitted the required selection of 500 ft in the altitude window of the mode control panel. The first officer, performing the pilot monitoring duties, did not detect this omission.
Autopilot Behavior and Manual Intervention
As the aircraft descended to 2,000 ft, the autopilot began to level off instead of continuing the descent to 500 ft. This deviation placed the aircraft above the desired descent profile. In response, the captain executed an unplanned manual intervention without informing the first officer of their intention. At the same time, the flight crew were attempting to complete the final landing procedures. This sequence of events led to an unexpected increase in workload and reduced the first officer's situation awareness.
Task Shedding and Missed Checklist Items
Workload is defined as the interaction between a specific individual and the demands imposed by a particular task, representing the cost incurred by the human operator in achieving a certain level of performance. An individual has finite mental resources that can be allocated to tasks, and these resources vary with experience, training, and stress levels. When workload becomes excessive, individuals may shed tasks either efficiently (by eliminating low-priority tasks) or inefficiently (by abandoning tasks that should be performed).
In this case, likely in response to increased workload and the absence of crew coordination, the flight crew missed required checklist items: the final flap and speed brake selections. The stabilized approach criteria required the aircraft to 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 the selection was made in time, the flaps did not reach the required position until the aircraft descended through 875 ft above the airport elevation.
Stabilized Approach Criteria and Missed Announcements
The first officer identified that the flap selection was late and that the stabilized approach criteria had not been met. However, because the descent rate, speed, and profile were within the criteria, the first officer 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 continued. The first officer also did not identify that the speed brake landing procedure action was not completed.
Descent Rate Exceedance and Speed Brake Issue
As the approach continued, the descent rate exceeded the stabilized approach criteria for a period of 9 seconds. This exceedance was momentary and not excessive, and thus 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 a missed approach. Instead, the missed action was quickly rectified by the captain, and the approach continued.
Conclusion
The sequence of events highlights the impact of workload and crew coordination on adherence to standard operating procedures during a visual approach.