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

1.6.4 Air data and inertial reference system (ADIRS)System overviewThe air data and inertial reference system (ADIRS) provided important informationabout the outside environment (such as air pressure and temperature), the aircraft’sstate relative to the outside air (such as airspeed, altitude and angle of attack), andthe aircraft’s state relative to the Earth (position, motion and orientation).To provide redundancy, the ADIRS included three air data inertial reference units(ADIRU 1, ADIRU 2, and ADIRU 3). Each was of the same design, provided thesame information, and operated independently of the other two. ADIRU 1 fromQPA is shown in Figure 7.Figure 7: ADIRU 1 (ADIRU 4167) from QPAEach ADIRU had two parts, an air data reference (ADR) part and an inertialreference (IR) part, which were integrated into a single unit. The two parts sharedsome common modules, such as the central processing unit module. In most cases,if one of the two parts failed, the other could still operate.Overall, the ADR outputted about 30 flight data parameters and the IR outputtedabout 60 flight data parameters. Examples are provided in Table 1. Apart from theflight data, the ADR and IR also transmitted documentary data (such as the ADIRUpart number and serial number), status data (such as the operating mode), and faultdata (of the ADR, IR and system inputs).- 13 -