Airbus says pilot misunderstood use of sidestick position indicator, causing him to inadvertently reduce pitch-up after VR
The Airbus Emirates A340-300 take-off overrun incident at Johannesburg in April was caused by an elementary blunder in the crew's use of instruments to judge pitch attitude during rotation, Airbus says.
Flight International has learned that the crew misused an indicator showing sidestick position to select rotation angle - an unapproved and flawed technique - which resulted in the Dubai-bound A340-300 failing to get airborne until it had passed beyond the end of the 4,420m (14,490ft) -long runway. As the aircraft overran the runway end, it struck lighting, bursting three main gear tyres and damaging the flaps - which subsequently locked in a partly deployed position (Flight International, 20-26 April). After the incident on 9 April, the aircraft, with 230 people on board, returned to Johannesburg after dumping fuel.
The bizarre circumstances surrounding the incident were revealed in a flight operations telex (FOT) issued by Airbus to A330/A340 operators earlier this month, and confirmed to Flight International by the manufacturer's chief test pilot Jacques Rossay. The information has come to light following analysis of the flight data recorder and a reproduction of indications on the primary flight display (PFD).
Rossay says that the pilot flying incorrectly believed that the sidestick position symbol could be used to select pitch attitude for rotation. This is thought to be an unprecedented error, and Rossay cannot explain why the pilot thought it was a valid technique.
The position symbol - a white cross within a box designated by four right-angle marks - is superimposed over the attitude director indicator's (ADI) moving pitch scale on each pilot's PFD when on the ground, but the two displays are independent and therefore not referenced to each other.
The sidestick position indicator, which was introduced on Airbus's first fly-by-wire aircraft, the A320, in 1988, has two functions - for pre-flight control checks and to monitor sidestick inputs during the take-off roll.
According to the Airbus FOT, at the point of rotation - VR was 150kt (278km/h) - the pilot flying pulled the sidestick back and tried to set a pitch attitude of 9º by aligning the position symbol with the corresponding mark on the moving attitude scale. As aircraft pitch increased, the attitude scale moved down relative to the "aircraft symbol" and the pilot reacted by moving the sidestick to keep the cross at the same position on the scale. This action progressively reduced the pitch-up command, causing the A340's attitude to decline from a maximum of 6º nose up, to 3.5º.
For the A340-300, Airbus recommends that pilots rotate at a rate of around 3º/s to an attitude of 12.5º.
As the crew realised that the aircraft was failing to leave the ground, take-off/go-around (TOGA) thrust was set and unstick occurred at 175kt (325km/h), 17s after initial rotation, at a 9º pitch attitude.
In its FOT, Airbus reminds operators that the symbol "was not designed to be used during take-off rotation" and says that "the pilot flying must perform the rotation mainly head-up, using outside visual clues until airborne".
The official investigation into the incident is ongoing, with an interim report expected within a couple of months.
Emirates' senior vice-president for flight operations Chris Knowles recently resigned, but the airline has revealed no reason for his departure (Flight International, 8-14 June).
MAX KINGSLEY-JONES / LONDON