For the data-spike failure mode, the built-in test equipment of the LTN 101 air data inertial reference unit was not effective, for air data parameters, in detecting the problem, communicating appropriate fault information, and flagging affected data as invalid.
The modification to the BITE processes will enhance the potential for the ADIRU to cease data output and provide appropriate fault indications in the event of another instance of the data-spike failure mode.
The ADIRU manufacturer conducted a detailed review of options for improving the LTN-101 BITE so that another instance of the data-spike failure mode would be detected. The options included comparisons of the data and/or label fields that were expected to be outputted on certain parameters with the data and/or label fields actually outputted. However, during testing it was found that these modification options adversely affected the performance of high-frequency tasks.
Subsequently, at the aircraft manufacturer’s request, the ADIRU manufacturer enhancedthe wraparound monitor test on the dummy label to improve the ADIRU’s ability to detect data transmission failures. More specifically:
The ADIRU manufacturer advised in October 2011 that the enhancements had passed testing, with certification expected by the end of 2011.
