What happened
On 11 September 2021, a Boeing 737-800, registration G-FDZF, was performing a commercial passenger flight from Palma de Majorca to Aberdeen Airport. During the approach to Runway 3lar, the crew was notified by Air Traffic Control that they might need to discontinue the approach to allow a search and rescue helicopter priority.
At 2,250 ft amsl, the crew initiated a go-around. While the aircraft initially climbed, it began an unexpected descent as it approached the assigned altitude of 3,000 ft amsl. The aircraft dropped to a minimum altitude of 1,780 ft amsl, reaching a peak descent rate of 3,100 ft/min. During this period, the aircraft accelerated to 286 kt, significantly exceeding the selected airspeed of 200 kt. The tower controller noticed the deviation and alerted the radar controller, who then instructed the crew to climb. The crew eventually re-established the climb and stabilized the flight path after re-engaging the autopilot. There were no injuries and no damage to the aircraft.
The investigation
The AAIB examined flight data monitoring (FDM) records, radar data, and radio communications. The investigation established that during the go-around, the aircraft's pitch decreased and the autothrottle reduced power in anticipation of leveling off. However, the aircraft failed to meet the necessary criteria for the flight director to transition to altitude hold mode. As the aircraft descended, the crew retracted the flaps from 15 to 5, and then further to 1 and 0.
Investigators also reviewed the flight experience of the crew, noting that both the commander and the co-pilot had experienced significant periods without flying on the aircraft type in the 18 months prior to the incident. While the investigation did not establish a direct causal link between recent flying experience and the event, the possibility of reduced capacity to manage high-workload transitions was noted.