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

Step-changeA significant step-change of either AOA 1 or AOA 2 would trigger a 1.2-secondmemorisation period and have no effect on AOA FCPC input (see scenario A inFigure 29). If the change lasted for more than 1 second, the FCPC would reject therelevant ADR and, following the 1.2-second memorisation period, AOA FCPC inputwould be based on the average of AOA 3 and the remaining AOA value.A step-change less than the monitoring threshold would have a constant but veryminor effect on AOA FCPC input computations.RunawayA runaway (consistently increasing or decreasing value) of either AOA 1 or AOA 2would trigger a 1.2-second memorisation period when it reached the monitoringthreshold. The runaway value would subsequently have no effect on AOA FCPC input(see scenario B in Figure 29). Following the memorisation period, AOA FCPC inputwould be the average of AOA 3 and the remaining AOA value.Prior to reaching the monitoring threshold, the runaway value would have a brief,minor effect on AOA FCPC input .Spike(s)A single, short-duration spike in AOA 1 or AOA 2 would trigger a 1.2-secondmemorisation period, with the last valid AOA FCPC input used during that period.Following the memorisation period, AOA FCPC input would again be based on currentvalues of AOA 1 and AOA 2.The occurrence of any other spikes during the 1.2-second memorisation periodwould not trigger another memorisation period (see scenario C in Figure 29). Theoccurrence of a spike after the end of the memorisation period would trigger a newmemorisation period.Spike values 1.2 seconds apartFollowing the 7 October 2008 occurrence, the aircraft manufacturer identified ascenario in which deviations in only one of the three AOA values couldsignificantly influence AOA FCPC input . The scenario involved two spikes inAOA 1 (or AOA 2) with the following properties:• The first spike was different to the median of the three AOA values, triggering a1.2-second memorisation period. This spike lasted for less than 1 second.• The second spike was present at the end of the memorisation period (1.2 secondsafter the start of the first spike).- 74 -