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

• Although passengers are routinely reminded to keep their seat belts fastenedduring flight whenever they are seated, a significant number of passengers havenot followed this advice. At the time of the first in-flight upset, more than 60 ofthe 303 passengers were seated without their seat belts fastened. [Minor safetyissue]6.2 Other safety factors• In recent years there have been developments in guidance materials for systemdevelopment processes and research into new approaches for system safetyassessments. However, there has been limited research that has systematicallyevaluated how design engineers and safety analysts conduct their evaluations ofsystems, and how the design of their tasks, tools, training and guidance materialcan be improved so that the likelihood of design errors is minimised. [Minorsafety issue]• The large number of spurious warnings and caution messages that resulted fromthe anomalous air data inertial reference unit behaviour created a significantamount of workload and distraction for the flight crew.• Single event effects (SEE) have the potential to adversely affect avionicssystems that have not been specifically designed to be resilient to this hazard.There were no specific certification requirements for SEE, and until recentlythere was no formal guidance material available for addressing SEE during thedesign process. [Minor safety issue]• The LTN-101 air data inertial reference unit (ADIRU) model had ademonstrated susceptibility to single event effects (SEE). The consideration ofSEE during the design process was consistent with industry practice at the timethe unit was developed, and the overall fault rates of the ADIRU were within therelevant design objectives. [Minor safety issue]• Industry practices for tracking faults or performance problems withline-replaceable units were limited, unless the units are removed forexamination. Consequently, the manufacturers of aircraft equipment haveincomplete information for identifying patterns or trends that can be used toimprove the safety, availability or reliability of the units. [Minor safety issue]• There has been very little research conducted into the factors influencingpassengers’ use of seat belts when the seat-belt sign is not illuminated, and theeffectiveness of different techniques to increase the use of seat belts. [Minorsafety issue]• Although passengers are routinely advised after takeoff to wear their seat beltswhen seated, this advice typically does not reinforce how the seat belts shouldbe worn. [Minor safety issue]6.3 Other key findings• As of the end of 2009, A330/A340 aircraft had accumulated over 28 millionflight hours. The occurrence on 7 October 2008 was the only occasion whenincorrect data from an air data inertial reference unit had resulted in inadvertentelevator commands. This in-service performance was consistent with therelevant certification requirements.- 214 -