What happened
On 4 December 2023, a Boeing 737-8200, registration EI-HET, was performing a commercial passenger flight arriving at London Stansted Airport. During the approach in instrument meteorological conditions (IMC), the crew attempted to intercept the glideslope from above. As the aircraft approached the runway, the altitude selector in the mode control panel was set to 100 ft.
At approximately 3.6 nm from the runway, the commander initiated a manual go-around. Because the missed approach altitude (MAA) of 3,000 ft had not been updated in the altitude selector, the flight directors continued to command a climb. The aircraft subsequently climbed through the 3,000 ft limit, reaching a maximum altitude of 4,030 ft amsl.
Upon realising the level bust, the pilot flying initiated a descent. This manoeuvre resulted in a steep nose-down attitude of 17.7°, a descent rate of 8,880 fpm, and an airspeed of 295 KIAS. The aircraft reached a minimum height of 1,740 ft agl, triggering the Enhanced Ground Proximity Warning System (EGPWS) 'pull up' and 'sink rate' alerts. The crew eventually recovered the aircraft and stabilised for a subsequent landing.
The investigation
The AAIB examined flight data recorder (FDR) and cockpit voice recorder (CVR) information, alongside aircraft systems and maintenance records. The investigation focused on the crew's management of the approach and the automation settings.
Investigators found that the crew had not shared a common mental model regarding their position on the continuous descent profile. The investigation also looked into the impact of the high workload caused by multiple altitude and mode changes during the approach. Additionally, the manufacturer's analysis of the flight data was used to assess the potential for spatial disorientation, though the investigation concluded the nose-down input was likely a direct response to the altitude deviation rather than an illusion.
Findings
- The primary cause of the incident was that the missed approach altitude was not set in the mode control panel prior to the commencement of the go-around.
- The crew was attempting to intercept the glideslope from above, which led to the altitude selector being set to a value (100 ft) below the aircraft's actual altitude.
- The pilot flying became fixated on the flight directors and did not recognise that the automation was not commanding a level-off at the required 3,000 ft altitude.
- The subsequent descent was exacerbated by the pilot moving the thrust levers from a high-power setting to idle, creating a pitch/power couple that contributed to the excessive nose-down attitude.
- The crew failed to communicate effectively regarding their position on the approach profile, preventing early intervention.
Safety action
Following the incident, the operator implemented several safety measures, including:
- The introduction of a new 'Discontinued Approach Procedure' to be used when approach stability cannot be maintained.
- Mandatory learning modules for all pilots regarding correct go-around procedures.
- The implementation of a new training package for high-energy approaches and non-standard go-around scenarios.