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

• inertial reference input/output module, which interfaced with the sensorelectronics module, received GPS data, and sent the final processed IR data toother systems• central processor unit (CPU) module, which was the main controlling andprocessing module (section 3.2.2)• monitor module, which provided some basic BITE logic and common discreteinterfaces (such as warning, fail and on/off indications)• power supply module, which converted the aircraft power to the variousvoltages used by the other modules.The ADIRU also contained:• a set of inertial instruments, comprising rotation (gyro) and acceleration sensors• a motherboard to electrically connect the internal modules and other components• a rear connector panel, including multiple separate output databuses (eight forADR data and four for IR data).• To achieve a high degree of fault tolerance, the ADIRU included BITE thatprovided monitoring and for isolation of faults within the unit. The BITE wasdesigned so that a wide range of ADIRU functions were monitored and a highproportion of faults would be detected by the ADIRU itself. In addition to faultdetection, the ADIRU’s BITE recorded routine maintenance information. BITErecords were stored in memory chips within the various modules. Furtherinformation on the operation of BITE functions of potential relevance to thedata-spike failure mode is provided in section 3.7.3.2.2 CPU moduleThe CPU 123 module performed the following functions:• monitored and controlled the other modules• conducted BITE tests, and managed and recorded BITE data• received data from the unit’s other modules, including flight data from the airdata input/output module and the inertial reference input/output module• processed the data (such as performing corrective calculations)• packaged the data in a format suitable for outputting to other aircraft systems(section 3.3.2)• sent the resulting data to the two input/output modules, which sent the data tothe other systems.ADR data was not passed through the inertial reference input/output module, and IRdata was not passed through the air data input/output module. Consequently, theCPU module was the only area within the ADIRU with the potential to directlyaffect ADR data, IR data and BITE memory. 124123124A CPU is the part of a digital computer system that executes instructions from a computerprogram or programs. It normally refers to a single integrated circuit.Other areas common to the ADR and IR parts were the power supply module, monitor module,rear connector panel and the motherboard. Although the power supply module, monitor module,- 111 -