When developing the A330/A340 flight control primary computer software in the early 1990s, the aircraft manufacturer’s system safety assessment and other development processes did not fully consider the potential effects of frequent spikes in the data from an air data inertial reference unit.
The manufacturer reviewed the FCPC algoirthms for processing other ADIRU paramters, and also incorporated the lessons learnt about incorrect input data patterns into its guidance for system designers.
Following the 7 October 2008 occurrence, the aircraft manufacturer reviewed the FCPC algorithms for processing each ADIRU parameter on the A330/A340 aircraft. The review examined the amplitude, duration and frequency of data spikes that could potentially affect the FCPC’s control of the aircraft’s flightpath. In addition to data spikes, other potential incorrect data patterns were also considered. Based on this review, modifications were made to the algorithms for processing a number of the ADIRU parameters used by the FCPCs.
In addition to the A330/A340, the manufacturer also reviewed the algorithms used for processing ADIRU parameters by the flight control computers on the A320 and A380 aircraft.
The manufacturer also advised that it will apply the lessons learnt from the 7 October 2008 occurrence in terms of the types of incorrect data patterns to be taken into account during future design definition and modification. Accordingly, modifications were made to its guidance document ABD0200 (Guidelines and requirements for the system designers).
