An Embraer E190 operated by Alliance Airways sustained a sharp descent close to terrain owing to the crew’s mode confusion.
The incident occurred on 24 August 2023 as the aircraft, VH-UYN, approached Alice Springs from Darwin, says the Australian Transport Safety Bureau.
The crew was originally to overfly and conduct a circuit to runway 12, but accepted a change of plan when air traffic control offered a shortened track and a visual approach, which required a track to waypoint ADLIM.
“As the aircraft tracked to the waypoint, the crew configured the aircraft with high drag to expedite the aircraft’s descent,” says ATSB.
“However, the rate of descent was higher than the crew anticipated and attempts to arrest the rate of descent were not immediately successful. The aircraft descended below 1,800ft [above ground level] with a rate of descent above 3,000ft/min. When the aircraft’s automation was not responding to the flight crew inputs in the way the crew anticipated, the crew disconnected the autopilot and took manual control of the aircraft.”
The ATSB subsequently found that the pilot flying had inadvertently switched the flight mode from FLCH (flight level change) to FPA (flight path angle). The captain did not notice the change because he was looking outside the aircraft monitoring terrain.
The flight mode change, however, resulted in the aircraft sharpening its descent, even as the pilot flying attempted to select a higher altitude. This led the crew to deactivate the autopilot and take manual control.
The crew subsequently landed the aircraft without further incident. There were no injuries among the four crew and 63 passengers.
“This incident highlights how important continuous attention to the autoflight system modes displayed on the primary flight display is to situation awareness,” says the ATSB.
“The ATSB reminds flight crews the importance of continually monitoring descent profiles, irrespective of the type of approach being flown and the level of automation being used.”
