Clearance of Flight-Control-System Software with Hardware-in-Loop Test Platform

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The Indian Light Combat Aircraft has flown more than 2000 flights, including trainer and naval variants, without encountering any major faults in the flight safety-critical fly-by-wire control software. This is partly due to the stringent quality control and rigorous testing of the control-law and air-data-system algorithms carried out on various ground platforms before flight. One of these ground test platforms is the hardware-in-loop test platform (Iron Bird). The processing of tolerance bounds to define the pass/fail criteria is an algorithmic development. It guarantees the correctness of the modules, if the set of inputs generates a set of outputs within processed tolerance bounds. This paper presents the philosophy behind the design of test cases and the tools developed to evaluate the control-law and air-data-system modules on the Iron Bird platform, and the procedure to clear the test results. The computation of tolerance bounds and algorithms for their processing have been evolved over a period based on several criteria, testers’ experience, and the experience gained during various levels of testing of air-data-system and control-law algorithms. This process yielded excellent results, and is accepted as a formal clearance methodology for the onboard safety-critical fly-by-wire system software.