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

EMI from other aircraft systems (such as the aircraft’s power supply or radiotransmitters) was more difficult to discount than EMI from other sources. This isbecause it was not possible to determine or reproduce the exact electromagneticenvironment that existed within the aircraft at the time of the occurrences, andbecause other aircraft systems had the potential to produce much stronger emissionsthan the other sources. However, there was still sufficient information availablefrom the unit testing, aircraft testing and other sources to conclude that this optionwas still unlikely.The other potential trigger that was relatively difficult to discount was SEE. In theabsence of testing information from the affected units, there was insufficientinformation to make a definitive conclusion.3.7 ADIRU built-in test equipment operation3.7.1 BackgroundA wide range of ADIRU functions and components were monitored and/or testedby the BITE, including:• ADM status• ADM and external sensor data integrity• inertial sensor environment and data integrity• input databus integrity• ADR output data consistency (between ADIRUs)• air data and inertial data analogue-to-digital conversion• volatile and non-volatile memory integrity• BITE memory integrity• power supply quality and status• CPU operation and arithmetic• output parameter range• output databus integrity.As part of the safety analysis that was conducted during the development of theLTN-101 (section 3.8), the ADIRU manufacturer estimated that the BITE providedthe following failure detection rates (that is, the percentage of failures that theADIRU would detect):• 98.5% of CPU module failures• 94.5% of air data input/output module failures• 94.8% of inertial reference input/output module failures• 96.0% of power supply failures• 92.1% of monitor module failures• 93.5% of failures overall.- 151 -