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

position 1 on QPA. Further details of that event are discussed in section 1.16.2 andAppendix D, and further information on the service history of unit 4167 isdiscussed in section 3.5.4.BITE data from ADIRU 1The aircraft’s three ADIRUs were removed to download the units’ BITE data andconduct examination and testing. 61The BITE data from ADIRU 1 showed no fault messages from the occurrenceflight. Given the fault messages recorded by other systems related to ADIRU 1,some fault messages should have been recorded. In addition, several routinemessages normally stored in BITE memory were either not recorded or hadanomalies. These included:• An alignment record should have been recorded after the ADIRU was turned onin Singapore. It was not recorded.• A routine NAV update record should have been recorded when the unit was shutdown at Learmonth. It was not recorded.• Routine elapsed time interval (ETI) 62 timestamps should have been recordedduring the flight. The ADIRUs were on for 14.8 hours before being shut down at1525. However, the ETI observed at turn on at the manufacturer’s test facilitywas about 0.7 hours after takeoff.• Routine temperature records should have been recorded every hour. None wererecorded after the start of the event (0440).Subsequent analysis indicated that the absence of recorded fault messages wasassociated with a problem in storing of BITE data rather than a problem with theexecution of the BITE tests themselves (section 3.7).BITE data from ADIRUs 2 and 3The BITE data from ADIRUs 2 and 3 showed that all the routine BITE messageswere correctly recorded. The data did not show any fault messages related toADIRUs 2 and 3, but did show fault messages related to the way ADIRU 1transmitted data to other aircraft systems.Although the three ADIRUs were essentially independent units, they exchangedsome ADR data and each unit monitored the others’ transmission of that data. Morespecifically:• The IR part of an ADIRU required certain ADR parameters for its computations(for example, true airspeed data was required in conjunction with groundspeedto determine the wind speed and wind direction).6162ADIRU 1 (unit 4167) was removed from the aircraft at Learmonth prior to any data downloads orfunctional testing of the other units on the aircraft. The other two units were removed after theaircraft was ferried back to Sydney. All three units were sent to the ADIRU manufacturer’sfacilities in Los Angeles in the US for data download and testing under the supervision of theATSB and other investigation agencies.The ETI was the total operating time of the ADIRU, from turn on to turn off.- 52 -