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

position, and the faulty unit was swapped to the FCPC 1 position and then replacedby 2K2007270. At the time of the replacement (13 June 2008), maintenancepersonnel conducted a series of tests and inspections to confirm that the FCPCswere operating normally.BITE download and unit testingFollowing the occurrence, the three FCPCs were removed from the aircraft andexamined by an authorised agency. The key results of this examination were:• Each FCPC was loaded with identical, uncorrupted operational software.• The BITE data was downloaded from each FCPC, and no faults relating to theoccurrence flight were found. 66 Both FCPC 2 and FCPC 3 contained faults fromearlier flights that were unrelated to the pitch-downs.• Each of the computers was subsequently tested, and no fault was found withFCPC 1 or FCPC 2. FCPC 3 failed a lightning protection test on one input. Theaircraft manufacturer advised that the relevant input was not used when anFCPC was installed as FCPC 3, and therefore the problem was unrelated to thepitch-downs.A review of the FCPC operational logic found that the EFCS faults that wererecorded on the PFR were due to self-monitoring discrepancies detected by theFCPCs during the pitch-downs, and that they were not associated with any physicalfaults of the computers (section 2.2.2). However, a problem was identified withhow the FCPC software was designed to manage incorrect AOA data (section 2.1).1.12.8 FMGEC performance reviewThe FMGECs were manufactured by Thales Honeywell (part numberC12858BA02). Service history details for the two units were as follows:• FMGEC 1 (serial number Q00173002571) was manufactured in February 2003.It had undergone a repair in April 2007 before being fitted to the aircraft.• FMGEC 2 (serial number Q00173003903) was manufactured in July 2007 andfitted new to the aircraft in April 2008.A review of the aircraft’s technical log entries related to the FMGES system for the12 months prior to 7 October 2008 identified no faults or problems related to theoccurrence.Each FMGEC had two channels as follows:• Command (COM) channel. The COM channel issued autopilot controlcommands to the EFCS, and it based its computations on all three ADIRUs(using the median or middle value of each relevant parameter).• Monitor (MON) channel. The MON channel also computed autopilot controlcommands, but based its computations on one ADIRU. FMGEC 1’s MONchannel used ADIRU 1, and FMGEC 2’s MON channel used ADIRU 2. 6766The FCPCs were interfaced to the CMS and FWS through two flight control data concentrators(FCDCs). Fault messages such as PRIM 1 PITCH FAULT, PRIM 3 FAULT and PRIM 2 PITCHFAULT were stored in the FCDC BITE rather than the in FCPC BITE.- 55 -