In-flight upset - 154 km west of Learmonth, WA, 7 October 2008,

A subsequent simulation confirmed that the 10° elevator deflection recorded on theFDR was the result of 4° of high AOA protection and 6° of anti pitch-upcompensation.The aircraft manufacturer advised that, for the situation that occurred during the twopitch-downs, the two corrective mechanisms remained active as long as theAOA FCPC input was above the triggering threshold. This period was about 1.8 secondsfor the first pitch-down. During this period, the flight crew’s sidestick inputs wouldhave had no influence on the aircraft’s pitch.Simulation of AOA values for second pitch-downThe same process was used to determine the AOA values required to replicate thesecond pitch-down (at 0445:08). A single memorisation period with different spikevalues and durations did not match the recorded elevator movements. Furtherstudies identified a more complex scenario that did match these movements, andthis scenario involved at least four spikes in succession and triggering twomemorisation periods in AOA FCPC input , as shown in Figure 31. 86Figure 31: AOA values used in simulation study for second pitch-downThe aircraft manufacturer also advised that the matching scenario required that thecontrol law reverted to alternate law at about the time of the fourth spike.Consequently the high AOA protection was not available after this time, and therewas only 6° of elevator deflection from the anti pitch-up compensation. This figurematched the maximum nose-down elevator position of 5.4° that was recordedduring the second pitch-down.Based on this scenario, the flight crew’s sidestick inputs would have had noinfluence on the aircraft’s pitch for about 2.8 seconds during the secondpitch-down.86One of the spikes in the matching scenario was 16.9°. The recorded values of AOA 1 spikes on theFDR at about this time were 50.625°, but values of 16.9° were recorded later in the flight(section 1.11.4).- 80 -