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

development to ensure compliance with the specifications. The specificationsincluded resilience to factors such as:• physical forces (including accelerations, shock, vibration, explosion and airpressure differentials)• temperature (including extremes, variation and loss of cooling air)• contaminants (including sand and dust, fungus, salt spray, fluids and humidity).Short-term environmental factors, including temperature and vibration may bereproduced in a test laboratory, and others such as corrosion, contamination anddamage from mechanical stress, may be identified by detailed visual inspection.The investigation carried out a series of inspections and tests on ADIRU 4167 (and,to some extent, ADIRU 4122) to identify whether it was susceptible to, or had beendamaged by, environmental factors. These activities included (see alsoAppendix E):• detailed visual inspection of the units’ interior and exterior, includingmicroscope examination of the modules after their removal from the units• vibration testing• environmental stress screening, incorporating 15 hours of temperature cycleswith power cycling at temperature extremes to attempt to induce a malfunction• highly accelerated stress screening, incorporating temperature and vibrationextremes close to the design limits of the unit• a test in which the unit was covered in a heat shroud and run continuously whilein a heat-stressed state.No relevant faults or signs of environmental effects were observed on the ADIRUsand there was no recurrence of the data-spike failure mode throughout the testing.Operational details of the occurrence flights were also examined and no factorswere identified that would have produced any unusual environmental conditions.3.6.5 Electromagnetic interferenceBackgroundElectromagnetic interference (EMI) is an undesired disturbance in the normaloperation of an electrical system as a result of electromagnetic emissions (oftentermed ‘noise’) from another source. Those emissions could originate from:• other aircraft systems• other onboard sources, including cargo and personal electronic devices (PED)carried by passengers• external artificial sources, such as ground-based radar sites and communicationsfacilities• natural sources, such as electrical storms and electrostatic discharge.Electromagnetic emissions can take the form of radiated emissions (disturbances inthe surrounding electromagnetic field, such as radio waves) or conducted emissions(undesired variations or ‘noise’ in the voltage or current carried by a wire or set of- 138 -