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

etween the values of any of the four altitude parameters. The FDR recordedstandard altitude, while the QAR recorded standard altitude and baro-correctedaltitude #1. In summary, the altitude values that correlated with some data spikescould have originated from any of the four altitude parameters.Other parametersA review of some of the other recorded data did not identify any other salientmatches between the binary values of the different ADIRU parameters. However,most of the ADIRU parameters were not recorded, and most of the data for eachparameter was not recorded. In addition, the nature of the IR data made it difficultfor the investigation to identify spikes in that data and to establish whether anypatterns existed. As discussed in section 1.11, the IR parameters rapidly divergedfrom realistic values and oscillated between unrealistically large values at varyingrates for the remainder of the flight.3.3.5 Data-spike patterns for the 27 December 2008 flightFor the 27 December 2008 occurrence, there was only a 24-second period whenspikes were outputted from ADIRU 1 before the ADR was switched off. Thecomputed airspeed spikes appeared to correlate with altitude data in a similar wayas for 7 October 2008 event, but there were too few spikes recorded to form adefinitive conclusion. There were no Mach or AOA spikes recorded. Furtherinformation on the FDR and QAR data are provided in Appendix D.3.3.6 SummaryFor the 7 October 2008 occurrence, there was a clear match between the values ofmost of the Mach data spikes and the concurrent values for altitude, both at cruiseand during the descent. There was also some evidence of data spikes for computedairspeed matching with altitude values in both the 7 October 2008 and 27 December2008 occurrences, and a possible relationship between the AOA spikes and altitudevalues in the 7 October 2008 occurrence.The investigation was unable to determine the extent to which other patterns existedin the data spikes because of limitations in the recorded data. The investigation wasalso not able to determine whether the repeated values of some data spikes were dueto the spike values being stored in memory, or due to the spike values resultingfrom the exchange of data with another parameter that did not vary during theperiod of interest (such as a documentary data, status data or fault data parameter).3.4 Data flow analyses3.4.1 BackgroundThe investigation examined the LTN-101 ADIRU’s data processing stages todetermine if there were indications of which stage or stages problems may haveoccurred. A simplified summary of the data flow used for most of the output- 121 -