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

dwells (sustained testing at a fixed frequency) at frequencies of interest, including:the transmission frequency range of the naval communication station, severalinternal clock and data frequencies used by the ADIRU, various aircraft radiotransmission and reception frequencies, and 19 in-flight entertainment (IFE) systemoperating frequencies.The naval communication station transmitted at a frequency of 19.8 kHz. It wasimpracticable to test this frequency for radiated susceptibility. However, ifemissions at this frequency were to affect any aircraft system, they would mostlikely couple onto the aircraft wiring rather than directly to any line-replaceable unit(LRU) due to the very long wavelength of low-frequency transmissions.Accordingly, conducted susceptibility testing was the most appropriate way ofassessing the potential impact of such emissions on an LRU such as an ADIRU.For ADIRU 4167 and the exemplar unit (4461):• During radiated susceptibility testing in the 40 to 60 MHz range and at 100 V/m,both units exhibited an ARINC 429 databus transmission fault. Inspectionsrevealed that databus shield terminations had broken loose on both units. Thetesting sequence was completed with no further failures. The equipment wassubsequently repaired and testing at the same frequency range and signalstrength was repeated. The failure did not repeat on either unit.• During vibration testing, some IR output data values exceeded the test’s datavariation tolerances, which were used to detect excessive variations in theADIRU’s output data. These exceedances were attributed to normal inertialdrift, which was exacerbated by the vibration imposed on the ADIRU, as well asscaling errors in the test software. Accordingly, the variations were considered aresult of minor problems with the test procedure design.These issues were not considered relevant to the occurrences under investigation.No other problems were identified.The full range of EMI testing required significant resources. ADIRU 4122 was notsubjected to EMI testing because all involved parties agreed that such testing wouldnot provide additional useful information in view of the results of the EMI tests thatwere performed on ADIRUs 4167 and 4461.Extended EMI testsADIRU 4461 was also subjected to additional environmental tests related toDO-160C and designed to establish typical ADIRU behaviour at high radiatedelectric field strengths and conducted currents, particularly at certain frequencies ofinterest. These tests consisted of:• conducted susceptibility tests up to 375 mA, or 2.5 times the DO-160C level• radiated susceptibility tests from 30 MHz to 100 MHz at 200 V/m, or twice theDO-160C level• radiated susceptibility tests from 100 MHz to 18 GHz at 250 V/m, or 2.5 timesthe DO-160C level• measurement of emissions between 150 kHz and 1.215 GHz with the ADIRUenclosure lid removed, to detect any abnormal emissions resulting from ahardware defect.- 251 -