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

The aircraft had a technical log that contained records of in-service maintenance,including reports from the flight crew. A review of technical log entries for theaircraft’s relevant systems identified a previous event on 12 September 2006 thatinvolved similar warnings and caution messages but no pitch-down events(section 1.16.2).The investigation also reviewed the aircraft’s maintenance records, focusing on theADIRUs, FCPCs, FCSCs, FMGECs, AOA sensors and probe heat computers(PHCs). The review covered component and defect histories, modification status,service bulletins, task cards and maintenance schedules. Nothing else of relevanceto the investigation was found. Further details on the service history of the relevantsystems are provided in section 1.12.1.7 Meteorological informationThe flight crew reported that, at the time of the occurrence, the weather was fineand clear and there was no turbulence. Cabin crew and passengers provided similarreports.An assessment of the weather conditions by the Australian Bureau of Meteorologystated that, at the time of the occurrence, the aircraft appeared to be in the vicinityof the sub-tropical jet stream and well south of any significant convection activity.Turbulence at a moderate or greater level was unlikely to have influenced theaircraft at the time of the occurrence.An examination of information from the aircraft’s FDR found that the verticalacceleration data prior to and during the two in-flight upsets was not consistent withthe effects of moderate or severe turbulence (section 1.11.5).1.8 Aids to navigationNot applicable to this occurrence.1.9 CommunicationsFor external voice communications, the aircraft was equipped with twohigh-frequency (HF) radios, three very high frequency (VHF) radios, and a satellitecommunications system (SATCOM). The aircraft could also transmit its positionautomatically using the automatic dependent surveillance-broadcast (ADS-B)system.The aircraft was also equipped with an aircraft communications, addressing andreporting system (ACARS). ACARS used VHF radio or SATCOM to transmitroutine flight operations and engineering data to the operator’s maintenance watchpersonnel. ACARS transmitted data intermittently as required. Fault messagesrecorded by the CMS were included in ACARS reports, and maintenance watchwas able to view these reports during their communications with a flight crew.every 10 years, commensurate with the increasing complexity of those checks. A and B checkswere generally performed at airport gates while C and D checks were performed in maintenancehangars.- 31 -