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

• Normally the IR part would use the ADR part from the same ADIRU to obtainthis data. If this ADR part was not available, then the IR part could source theseparameters from another ADR.• In order to obtain ADR information from another ADIRU, each unit had adigital air data system (DADS) input from the two other ADIRUs. The DADSinputs supplied true airspeed and altitude data.• If there was a problem with the ADR data received by an IR part, then theaffected ADIRU would record a fault in its BITE and generate a fault message.• Each ADIRU also performed input range monitoring of the parameters that wereoutputted over the DADS databuses. The acceptable ranges were 0 to 599 kts fortrue airspeed and -2,000 to 50,000 ft for altitude.For the 7 October 2008 flight, ADIRU 2 and ADIRU 3 both recorded faultmessages that indicated problems with the true airspeed or altitude data outputtedfrom ADIRU 1 to the other ADIRUs. These messages are summarised in Table 15.Table 15: BITE summary from ADIRUs 2 and 3 for 7 October 2008 occurrenceTime 63 ADIRU Fault description Comment0440:30 ADIRU 2ADIRU 3Input databus refresh ratefailed (class 3)Input databus refresh ratefailed (class 3)0506:36 ADIRU 3 Input databus refresh ratefailed (class 1)0512:00 ADIRU 3 Failure detection andexclusion still GPSSU 1(class 3)0512:54 ADIRU 2ADIRU 3Input data SSM failed(class 3)Input data SSM failed(class 1)Altitude and/or true airspeed werenot being received from ADIRU 1at the designed rate.Altitude and/or true airspeed werenot being received from ADIRU 1at the designed rate.The GPS satellite failure detectionand exclusion function failed; themonitor determined that therewere several data inconsistenciesbut was unable to isolate them toa specific source.Altitude and/or true airspeed werereceived from ADIRU 1 with theSSM field set to ‘failure warning’or ‘no computed data’. 640523:24 ADIRU 2 Input range failed (class 3) Altitude and/or true airspeedreceived from ADIRU 1 were outof range.Normally these types of fault messages would be class 3 maintenance faults.However, at 0443:45 the flight crew switched the ATT HDG switch to the CAPTON 3 position. IR 3 then provided the data for the captain’s flight displays. As thecaptain’s AIR DATA switch remained on the NORM position, ADR 1 was still theprimary source of air data for the captain’s systems, and therefore became theprimary source of air data for IR 3. Consequently, any problem IR 3 detected withADR 1 after 0443:45 became more significant and resulted in a class 1 failure. The6364The ADIRU BITE recorded fault messages to a resolution of 6 seconds.A review of the QAR data showed that at 0513 there were spikes in standard altitude, Mach andwind speed (derived from true airspeed). True airspeed was not recorded by the FDR or QAR.- 53 -