What happened
On the morning of 27 October 2024, a South African Airways Airbus A330-300, registration ZS-SXJ, was operating a scheduled commercial flight from Cape Town International Airport to O.R. Tambo International Airport. While cruising at flight level 410, the aircraft encountered sudden clear air turbulence near Loxton in the Western Cape.
The turbulence triggered significant pitch oscillations and a rapid increase in airspeed. The pilot flying noticed the speed trend vector accelerating toward the overspeed protection limit, reaching approximately 40 knots into the red barber pole area. During the disturbance, the aircraft experienced a 0 G-load factor. At the time, the cabin crew were serving breakfast, and the sudden movement caused food and hot beverages to spill, resulting in four cabin crew members sustaining minor to serious injuries.
The investigation
An investigation by the SACAA AIID established that the aircraft's weather radar did not detect the turbulence because it was clear air turbulence, which does not show on radar. The investigation examined the flight crew's response to the overspeed condition and the aircraft's mechanical performance.
Technical analysis and simulations conducted by Airbus revealed that the aircraft exceeded its maximum operating Mach number for 9 seconds. The investigation also found that the aircraft's structure remained undamaged following a post-incident inspection.
Findings
- The primary cause of the incident was the aircraft encountering clear air turbulence, which induced the vertical oscillations and subsequent overspeed condition.
- The pilot flying deviated from established Airbus procedures by disengaging the autopilot to manually manage the pitch, rather than following the recommended overspeed prevention technique of keeping the autopilot engaged and using speed brakes.
- The pilot monitoring did not intervene during the event, despite receiving overspeed warnings.
- There was evidence of poor Crew Resource Management (CRM), specifically regarding a lack of communication when the autopilot was disconnected and a failure to follow the Flight Crew Technique Manual (FCTM).
- The aircraft's weather radar was unable to provide warning as the turbulence was not associated with visible precipitation.