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

Flight crew pitch inputsDuring manual flight, the flight crew make pitch control inputs using theirsidesticks. Both the captain’s and first officer’s sidestick movements were recordedby the FDR.After the autopilot disengaged (0440:28), the captain’s sidestick showed activitythat was consistent with small control inputs. The first officer’s sidestick wasinactive.There was no sidestick input that correlated with the initiation of either pitch-down.In both cases, very soon after the pitch-down commenced, the captain applied backpressure to the sidestick to produce a nose-up input. Each was moderate andcommensurate with the response required to correct for the pitch-downs. The inputsdid not have any immediate effect on the recorded elevator position, but within1 to 2 seconds the elevator position started to correlate with the sidestick inputs.Figure 24 and Figure 25 show the sidestick pitch input parameters for the 10-secondperiod around each pitch-down.Trimmable horizontal stabiliser movementsThe range of the THS position was +2° (nose-down) to -14° (nose-up), andmovement was limited to approximately 1° per second. The FDR recorded the THSposition once per second, and the data showed that there was no movement of theTHS immediately prior to either of the two pitch-downs.Trim tank changesA fuel tank was located in the THS to allow for a reduction in the amount of noseuptrim that the THS needed to provide during flight. This in turn reduced the dragproduced by the THS and consequently the aircraft’s fuel consumption. The trimtank capacity was 6,230 L, which corresponded to a weight of 4,891 kg. 53 Fuel wastransferred automatically to and from the trim tank to maintain the aircraft’s c.g.within a target range.The FDR recorded the trim tank fuel quantity, and the data showed that 500 kg offuel was present at takeoff, reducing to a constant value of 440 kg during cruise.There was no change in the trim tank fuel quantity before either of the pitch-downs.TurbulenceRecorded flight data can help determine whether an aircraft has experiencedturbulence, with the vertical acceleration parameter being the key indication. Inflight, vertical acceleration values represent the combined effects of flightmanoeuvring loads and turbulence. Turbulence is indicated by a higher frequencyscatter in the trace while flight manoeuvring loads are more prolonged and correlatewith pitch and roll attitude changes.Figure 24 shows the vertical acceleration during the first pitch-down, and Figure 25shows the vertical acceleration during the second pitch-down. There was noevidence of any turbulence in the recorded data during these periods.53For a fuel specific gravity of 0.785 kg/L.- 44 -