What happened
On September 14, 2010, a Sichuan Airlines A319, registration B-6054, was performing flight 3U8949 on final approach to Runway 03 at its destination airport. The aircraft encountered severe weather characterized by a thunderstorm and a microburst, which produced sudden changes in wind direction and significant vertical downward airflow of approximately 30 knots.
As the aircraft intercepted the ILS, the autopilot attempted to maintain the glide slope by increasing the angle of attack. This led to a rapid decrease in airspeed, triggering a Low Energy Warning. Instead of following manual procedures to increase thrust, the crew attempted to manually adjust the target speed via the Flight Control Unit. This action, combined with the severe turbulence, caused the airspeed to drop to 74 knots, well below the normal approach speed. The aircraft subsequently entered a stall, with the angle of attack reaching 33.4 degrees and a maximum sink rate of 3,924 feet per minute. During the event, the aircraft experienced a significant right bank of 43.59 degrees and the simultaneous failure of both Flight Augmentation Computers (FAC1 and FAC2).
The investigation
The investigation, conducted by the CAAC with assistance from the French BEA and Airbus, analyzed decoded QAR data to reconstruct the aircraft's flight path and the impact of the weather. Investigators examined the aircraft's automated protection systems, specifically the Alpha Protection and Alpha Floor functions, to determine their effectiveness during the encounter. The investigation also reviewed the crew's compliance with the Airbus Flight Crew Operating Manual (FCOM) and their response to the Low Energy and Stall warnings.
Findings
- The primary cause of the incident was inappropriate pilot decision-making and handling during severe weather conditions.
- The crew failed to divert or stop the approach despite receiving multiple ATC updates regarding thunderstorms and other aircraft diverting to nearby airports.
- The crew did not follow the Quick Reference Handbook (QRH) procedures; specifically, they attempted to adjust target speed rather than immediately advancing the thrust levers when the Low Energy Warning occurred.
- Crew Resource Management (CRM) was ineffective, characterized by instinctive and simultaneous side-stick inputs from both pilots for approximately 12 seconds.
- The aircraft's automated protection systems, including Alpha Protection and Alpha Floor, functioned as designed, eventually helping to recover the aircraft from the stall.
- The microburst and associated windshear provided energy levels that exceeded the capacity of the automated systems to prevent the stall.