What happened
During the approach and landing phase, the flight crew experienced a significant increase in workload following an error with the altitude selector. The pilot flying (PF) failed to properly depress the selector and subsequently neglected to verify the flight mode annunciation (FMA) for the required change. This error led to a substantial loss of situational awareness regarding the aircraft's descent profile, specifically concerning the aircraft's altitude relative to its distance from the runway.
Driven by a preconception that the aircraft needed to avoid being high on the approach profile, the PF initiated a descent that breached the required altitude limit of 3,000 ft. This altitude was mandatory to maintain until the aircraft was established on final approach. The crew identified the deviation and began leveling the aircraft at approximately 2,000 ft shortly before air traffic control (ATC) notified them of the altitude breach.
The investigation
The investigation focused on the crew's management of the approach and the execution of monitoring duties. It was noted that while the pilot monitoring (PM) had not previously flown this specific approach, the monitoring role was not effectively performed. The investigation examined how the combination of high workload and the failure to verify flight mode changes contributed to the loss of descent profile awareness.