On 11 May a British Airways Boeing 747-400 carrying 283 people almost stalled just after take-off from Johannesburg following a spurious systems warning that automatically disabled some wing leading-edge high-lift devices.
South Africa's Civil Aviation Authority is carrying out a serious incident investigation of the event. CAA investigators explain that during the take-off run there was a false indication that the Nos 2 and 3 engine thrust reversers had unlocked, which automatically triggered retraction of the inboard wing leading-edge slats at the point of rotation for take-off.
The loss of the leading-edge high-lift devices resulted in the crew getting a stall warning stick-shake just after lift-off, but the crew kept the aircraft airborne and the slats redeployed less than a minute later.
The CAA says the thrust reverser unlock alert while the aircraft was still on the runway caused the system logic to act as if the aircraft was landing rather than taking off, and it retracted the slats to protect them against foreign object damage from reverse thrust. This is an automatic function when reverse is selected during landing.
The Rolls-Royce RB211-powered aircraft (G-BYGA) was bound for London carrying 18 crew and 265 passengers.
The incident occurred on 11 May at 20:35, according to the CAA, which says the flight data recorder was downloaded a week later on 18 May.
The authority says it has enlisted the co-operation of the UK Air Accidents Investigation Branch, the US National Transportation Safety Board, Boeing and BA. There was no power rollback as some sources have speculated, says the agency, and when the slats redeployed the crew climbed to a safe height, dumped fuel and returned to Johannesburg.
Boeing and BA say they are co-operating with the inquiry.