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A pilot's high workload, including data entry difficulties, while conducting an approach to land at Adelaide Airport in instrument meteorological conditions likely affected their situational awareness resulting in their aircraft descending below the assigned minimum altitude.
An Australian Transport Safety Bureau investigation into the incident details that on the morning of 12 August 2021, the twin-engine Aero Commander 500-S was conducting a private flight from Port Lincoln to Adelaide with a pilot and passenger on board.
After descending to 3,800 ft during the approach, the pilot was cleared by air traffic control to track direct to the GPS waypoint GULLY, the initial waypoint for the area navigation (RNAV) instrument approach into Adelaide.
However, the pilot reported having difficulties entering the RNAV approach into the aircraft's touchscreen multi-function display due to turbulence.
"Several factors including the environmental conditions, data entry difficulties, and the timing of the clearance for the GULLY waypoint, likely led to the pilot experiencing a high workload," ATSB Director Transport Safety Dr Stuart Godley explained.
By the time the pilot correctly input the approach into the system, the aircraft had just overflown the GULLY waypoint. This meant when the pilot then selected the 'Direct-To' option on the display, the autopilot commanded a sharp turn to the right, to commence an orbit to attempt to overfly the waypoint to recapture it.
The controller then began giving the pilot instructions, intending to vector the aircraft back to the waypoint, but a short time later, communications were lost.
"The ATSB found that during the approach the pilot had inadvertedly selected the incorrect radio frequency," Dr Godley said.
For about 4 minutes before contact was re-established, the aircraft continued on its assigned heading, but began descending below its assigned altitude.
"During this time, the approach controller attempted to contact the pilot and issued three terrain safety alerts. The lowest altitude the aircraft descended to was 2,480 ft, close to the highest point within 5 NM of the aircraft's track, which was 1,913 ft."
Once communications were re-established, the approach controller issued the pilot a terrain safety alert and instructed the pilot to climb immediately to 5,000 ft.
The aircraft then tracked to Adelaide Airport and landed without further incident.
Dr Godley said the event highlights the heightened workload pilots experience during the approach and landing phases of flight.
"Pilots must continuously monitor aircraft and approach parameters, and the external environment, to ensure they maintain a stable approach profile and make appropriate decisions for a safe landing," Dr Godley said.
"Distractions and unanticipated events can further increase a pilot's workload leading to undetected errors and a loss of situational awareness.
"During high workload phases of flight, pilots should remain focused on monitoring the aircraft instruments and avoid fixating on a problem."
You can find here the report: AO-2021-033: Flight below minimum altitude involving Aero Commander 500 S, VH-LTP near Adelaide Airport, South Australia, on 12 August 2021
Last update 01 March 2022
