Air data inertial reference units

There have been a very small number of incidents in passenger service that have been ascribed to software failure. The best-documented example is probably an in-flight upset on a Boeing 777 near Perth, Australia, in 2005. A contributing factor was found to be a software anomaly that allowed inputs from a known faulty accelerometer to be processed by the Air Data Inertial Reference Unit (ADIRU) (ATSB 2007). 

At 0440 26 UTC (local time 1240 26) one of the Air Data Inertial Reference Units (ADIRUs) started producing multiple intermittent spike signals, and the crew received a number of warning messages many of which were spurious and unhelpful. 

This diagram presents a much-simplified version of the A330 s Electronic Flight Control System, showing its control and protection systems architecture. Because of inadequate design analysis, a particular spike" failure mode in one single air data inertial reference unit (ADIRU) was able to lead to sudden pitch down of the aircraft when in level high-altitude cruise. 

Flight control systems require accurate angle of attack (AOA) data, which are provided by 3 redundant air data inertial reference units (ADlRUs). 

ADIRU Air Data and Inertial Reference Units Chapter 6... 

---