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

until a few years ago, were not directly considered in the aircraft certificationprocess. It stated that during the certification of the A330/A340, there was noreference to SEU or MBU and that it was unlikely that the phenomena were directlycovered. However, it noted that the system architectures were designed to protectthe aircraft from single-point failures by the use of design techniques, such ascommand and monitor channels and voting mechanisms. 155The US Federal Aviation Administration (FAA) advised during the investigationthat there were no current standards specifically targeting SEE faults. However, itstated that design assurance, fault tolerance and system safety assessments wererequired under FAR 25.1309, and that these requirements were intended to providetolerance to all foreseeable single failures regardless of their origin, and suchfailures would implicitly include SEE.As noted in section 3.5.2, the CPU module on units 4167 and 4122 did notincorporate EDAC, nor was it required by the aircraft manufacturer’s specification.However, the ADIRU did include some features that could detect and mitigate theeffects of a wide range of failures, including many failures that could have beentriggered by SEE. For example, the ADIRU’s program memory was periodicallychecked for integrity, and that check would have failed if the program memory hadbeen corrupted. This and other BITE functions are discussed in section 3.7.Space weather at the time of the occurrencesThe ATSB requested the Bureau of Meteorology’s (BOM) Ionospheric PredictionService to examine the space weather 156 at the time and location of the threeoccurrences (12 September 2006, 7 October 2008 and 27 December 2008).Geomagnetic observations from Learmonth and Darwin and cosmic radiationobservations from Hobart were examined. The conclusion by BOM was that thespace weather for the three occurrences was within the normal ranges for therelevant locations.Although the neutron fluxes 157 for the three occurrences were at around the normallevels, this still meant there were a significant number of particles present. Thenominal high-energy (greater than 10 million electron-volts) neutron flux is about5,600 neutrons per cm 2 per hour at 40,000 ft and 45° latitude (North or South). 158There is a very high variation of neutron flux with altitude (about 300 times higherat 40,000 ft than at ground level) and a minor variation with latitude (about fourtimes higher at the poles than at the latitude of the 7 October 2008 occurrence). The155156157EASA advised that during the development of the A350 and A380 it requested Airbus to considerthe effects of SEU and MBU on systems and equipment, and Airbus required equipmentmanufacturers to consider the effects of SEU and MBU and to mitigate these effects.‘Space weather’ refers to the variable environmental conditions in near-Earth space. It is distinctfrom the concept of weather within the atmosphere, and deals with phenomena involving plasma,magnetic fields, radiation and other matter in space. Space weather can have consequences atground level as well as effects in the upper atmosphere.Neutron flux is the number of neutrons passing through an area during a period of time. The unitof neutron flux used in this report gives the approximate number of neutrons that pass through anarea of one square centimetre (cm2) in 1 hour.158This figure was stated in IEC TS 62396 (discussed later in this section). High-energy neutrons arethose with an energy of 10 million electron-volts or more. The flux for neutrons between 1 to10 million electron volts is about 3,000 per cm 2 per hour for the same location.- 145 -