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

FDR process for recording ADIRU dataThe FDR recorded 11 ADIRU parameters (Table 1), and sampled most of theseparameters once per second.For all of the parameters except AOA, the FDR only recorded the data from one ofthe ADIRUs. The priority source of the recorded parameters was the same as thatselected for the captain’s flight displays (using the ADIRS switching controlsdiscussed in section 1.6.4). More specifically:• If the captain’s AIR DATA switch was set to NORM, then ADR 1 was thepriority source of the ADR parameters recorded on the FDR. If the switch wasset to CAPT ON 3, ADR 3 was the priority source. The switch position was notchanged during the occurrence flight.• If the captain’s ATT HDG switch was set to NORM, then IR 1 was the prioritysource of the IR parameters recorded on the FDR. If the switch was set to CAPTON 3, IR 3 was the priority source. The crew selected the switch to the CAPTON 3 position at 0443:45.In addition, if ADIRU 1 flagged one of its output parameters as ‘invalid’(section 1.6.8), then the FDR recorded that parameter from a different ADIRU. Thisswitching was done on a parameter-by-parameter basis, and the FDR returned tousing ADIRU 1 when that ADIRU again flagged its output data for the parameter asvalid.The only exception to this parameter switching was for AOA. 46 The FDR explicitlyrecorded two AOA values: one from the captain’s ADR source and one from thefirst officer’s AOA source. For this occurrence, as the ADR switch remained in theNORM position, the FDR recorded AOA 1 and AOA 2 for the entire flight.Because two values were recorded, the recording logic was configured so that therewas no switching of the source even if the data was flagged as ‘invalid’. 47The FDR also recorded a separate ‘Fail’ parameter for ADR 1, IR 1, ADR 2, IR 2,ADR 3, and IR 3. Each of these FDR parameters showed a fail value if a fault wasindicated by the relevant ADR or IR itself, or if the ADIRU flagged key parametersas invalid for more than 500 msec. 48 In other words, the presence of a fail value forADR 1 or IR 1 indicated that the FDR had switched to a new source for at leastsome parameters. 4946474849As discussed in section 1.16.4, each ADIRU outputted indicated and corrected AOA. The FDRand QAR only recorded corrected AOA, and all AOA data discussed in this report is correctedAOA.As the AIR DATA switch remained in the NORM position for the entire flight, the source ofAOA 1 was always ADR 1 (that is, the ADR part of ADIRU 1), and the source of AOA 2 wasalways ADR 2.The ADR parameters were standard altitude and/or computed airspeed, and the IR parameterswere pitch attitude and/or roll attitude.The fail indications on the FDR did not correlate exactly with the NAV IR 1 and NAV ADR 1ECAM caution messages that were generated by the FWS. The inputs for the FDR’s failparameters were provided by the aircraft’s DMCs rather than from the FWS. The triggering logicand conditions (for example confirmation times) for the FWCs and DMCs were not identical.Further information on the DMCs is provided in Appendix B.- 35 -