Investigators are probing an in-flight oscillation at cruise altitude which affected a South African Airways Airbus A330-300 bound for Malaysia.
The aircraft – flying from Cape Town to Johor Bahru on 27 October – had been cruising at 41,000ft when it started to oscillate in pitch, between nose-up and nose-down.
French investigation authority BEA says the movements were “slowly gaining momentum”.
The first officer observed the airspeed trend vector, which predicts airspeed based on the aircraft’s progression, increasing to 40kt in the overspeed protection range.
In order to avoid the overspeed the crew disengaged the autopilot and the aircraft gently reduced pitch to 1.5-2°. This halted the acceleration of airspeed.
BEA says the airspeed trend vector then indicated a 40-50kt change, towards the lowest-selectable speed and angle-of-attack protection range.
The aircraft (ZS-SXJ) subsequently diverted to Johannesburg.
Four occupants of the twinjet sustained minor injuries during the occurrence. BEA states that South African investigators are leading the inquiry.
