What happened
On 12 December 2012, a Beech C90GTI Kingair, registration G-MOSJ, was conducting a private flight into Belfast Aldergrove Airport. While being vectored by Air Traffic Control (ATC) for an ILS approach to Runway 25, the aircraft was operating in good weather conditions. The co-pilot was managing the flight controls while the commander was occupied with administrative tasks.
As the aircraft approached the localiser centreline, ATC issued a descent clearance to 3,000 ft accompanied by a left turn. The co-pilot programmed the autopilot with a vertical speed of 2,000 ft/min. The commander noted that this setting risked exceeding the flap limit speed and alerted the co-pilot. Following further instructions from ATC to descend to 1,700 ft, the commander briefly diverted his attention to record the new instructions.
During this period, the aircraft descended below the established ILS glidepath. The Aerodrome Controller observed the deviation on radar and alerted the Approach Controller. The controller subsequently notified the crew that they were below the glidepath and instructed them to execute a go-around and climb to 3,000 ft. After communicating with ATC, the commander requested to continue the approach visually. Having regained a stable profile, the aircraft was cleared to land.
The investigation
The investigation examined the cockpit actions, the automation settings, and the communications between the crew and ATC. The inquiry reviewed the commander's report, which highlighted a period of high workload involving simultaneous frequency changes, turns, and descent instructions. The investigation also analyzed the controller's observations, specifically the activation of the Funnel Deviation Alert (AFDA) when the aircraft deviated from its path.
Findings
- The crew experienced a period of high workload caused by rapid changes in instructions, including a late descent, turns, and a frequency change.
- The commander was distracted by the need to record ATC instructions.
- The delay caused by interacting with autopilot functions rather than manual flight control contributed to the deviation.
- The co-pilot's relative inexperience and the commander's momentary distraction were contributing factors to the incident.