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

7 SAFETY ACTIONThe safety issues identified during this investigation were communicated to therelevant organisations during the investigation. In addition, these organisations weregiven a draft report and asked to communicate what safety actions, if any, they hadcarried out or were planning to carry out in relation to each safety issue.For a critical or significant safety issue, the Australian Transport Safety Bureau(ATSB) expects the relevant organisation(s) to take safety action to address theissue. If appropriate safety action is not taken, the ATSB may issue a formal safetyrecommendation or a safety advisory notice.For a minor safety issue, the ATSB notes that the associated risk is consideredbroadly acceptable. The ATSB still encourages the relevant organisation(s) to takesafety action, but it does not issue a formal recommendation or a safety advisorynotice.When the ATSB has been advised of safety action in response to a safety issue, it ispublished in the final report.7.1 Flight control primary computer issues7.1.1 Algorithm for processing AOA dataSignificant safety issueThere was a limitation in the algorithm used by the A330/A340 flight controlprimary computers for processing angle of attack (AOA) data. This limitationmeant that, in a very specific situation, multiple AOA spikes from only one of thethree air data inertial reference units could result in a nose-down elevator command.Procedural changes issued by AirbusOn 15 October 2008, the aircraft manufacturer issued Operations EngineeringBulletin (OEB) OEB-A330-74-1, which was applicable to all A330 aircraft fittedwith Northrop Grumman ADIRUs. 201 The OEB stated that, in the event of a NAVIR [1, 2 or 3] FAULT (or an ATT red flag being displayed on either the captain’s orfirst officer’s primary flight display), the flight crew were required to select the airdata reference (ADR) part of the relevant ADIRU OFF and then select the relevantinertial reference (IR) part of the relevant ADIRU OFF. The problem was describedas a ‘significant operational issue’ and operators were advised to inform their pilotsof the OEB without delay and insert the procedure in the Flight Crew OperationsManual. A compatible temporary revision was issued to the Minimum MasterEquipment List at the same time.The OEB procedure was subsequently amended in December 2008 to cater for asituation where the IR and ADR pushbuttons were selected OFF and the OFF lights201Operators were advised of the OEB and the associated problem in an operator information telexthat was issued on 14 October 2008.- 217 -