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

Potential effects during different phases of flightThe two flight envelope mechanisms would not issue pitch-down commands whenthe aircraft was close to the ground. More specifically:• The high AOA protection had a confirmation time of 2 seconds when theaircraft was below 500 ft above ground level. As AOA spikes longer than1 second would result in the relevant ADR being rejected, this protection couldnot be activated by a multiple AOA spike scenario that occurred below 500 ft.• The anti pitch-up compensation was only available above Mach 0.65 and in theclean configuration. Therefore, this mechanism would not realistically occurduring final approach or initial climb situations, when the aircraft was operatingin close proximity to the ground.Following the 7 October 2008 occurrence, the aircraft manufacturer conductedflight simulations with the aircraft just above 500 ft and at typical approach speeds.Based on the high AOA protection command alone, 83 the decrease in altitude due toa pitch-down without a flight crew response was not significant (less than 100 ft).When the flight crew were asked to respond to the pitch-down, the decrease inaltitude was much less. During these simulated events, there was an autopilotdisconnection, but the flight crew easily recovered control.2.2 Examination of FCPC performance on 7 October 20082.2.1 Simulations to determine role and origin of elevator deflectionsThe aircraft manufacturer conducted a series of simulations to determine the natureof the factors that could have contributed to the pitch-downs on the 7 October 2008flight. These activities were performed using an engineering simulation tooldeveloped during the aircraft development process (see section 2.4.4).Effect of elevator deflectionsThe first simulation study used the elevator deflections recorded on the FDR andthe flight conditions present at the time of the first pitch-down to confirm theaircraft’s pitch movements during the event. The study found that the recordedelevator deflections were sufficient to explain the aircraft movement, whichconfirmed that turbulence did not contribute to the pitch-downs.Role of sidestick inputsThe second study used the flight crew’s sidestick pitch inputs that were recorded onthe FDR as inputs into the engineering simulation tool. It confirmed that thesidestick inputs were not sufficient to explain the recorded elevator deflections atthe start of the pitch-downs, and therefore another factor was involved in initiatingthese deflections.83Anti pitch-up compensation was not included as it would not realistically be available at thataltitude.- 78 -