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

Comparison of the three occurrences to other operationsThe three known data-spike occurrences occurred on two aircraft in the sameoperator’s fleet. The investigation examined if there were any unique aspects of theoperator’s aircraft, maintenance practices or operational practices that could havebeen related to the ADIRUs’ anomalous behaviour. No related factors were found.More specifically:• Aircraft QPA and QPG were manufactured at different times. The operatoradvised that QPA and QPG did not have any unique configurations or types ofaircraft systems that made them different to the operator’s other A330-303aircraft.• The aircraft manufacturer advised that the operator’s A330 aircraft did not haveany unique aircraft systems compared with the rest of the world A330/A340fleet. That is, each aircraft system used by the operator was also used by at leastone other operator that had LTN-101 ADIRUs fitted to its aircraft.• The aircraft manufacturer, operator and ADIRU manufacturer advised that therewas nothing unique about the operator’s processes for operating or maintainingits ADIRUs. All repairs and software upgrades were conducted by the ADIRUmanufacturer. All system tests conducted on the aircraft were conducted inaccordance with the manufacturer’s procedures.The aircraft manufacturer andoperator conducted a detailed examination of QPA’s ADIRS installation andconfiguration, focusing on the ADIRU 1 wiring and connections. No problemswere found.• A detailed review of the sequence of events in the 7 October 2008 occurrenceidentified that nothing unique or unusual occurred during the flight, either on theflight deck or in the cabin. Nothing unique or unusual was reported for either ofthe other two occurrences. The FDR data for both the 7 October 2008 and27 December 2008 flights showed nothing unique or unusual prior to the start ofthe anomalous ADIRU behaviour. There was no problematic cargo carried onany of the three flights.• The three occurrences happened during cruise; however, with medium or longdistance flights the majority of flight time involves cruise. All three occurred atdifferent times during each flight.• The three occurrences all took place on routes between Perth and Asia (eitherSingapore or Hong Kong), although there were significant distances between theoccurrence locations. The operator advised that about 19% of its A330 sectors in2008 were on flights between Perth and Singapore or Hong Kong and passed inrelatively close proximity to Learmonth. In addition, about 29% of its A330flights passed within 1,500 km of Learmonth. The investigation also identifiedthat other A330/A340 operators, including operators with LTN-101 ADIRUsfitted, conducted regular flights between Asian locations and Perth.1.16.3 Comparison to other A330/A340 occurrencesBetween 1992 and 2009, A330/A340 aircraft conducted over 28 million flyinghours with very few accidents or serious incidents. There have been no otheraccidents on A330/A340 aircraft associated with the flight control system providingpitch-down commands in response to incorrect ADIRU data.- 62 -