Ensuring Software Quality-Experiences of Testing Tejas Airdata Software

Two major safety-critical elements of the onboard software for the Tejas digital flight controlcomputer software are the control laws and the airdata algorithm. The airdata algorithm computesessential parameters like static and dynamic pressures, altitude, speed, angle of attack, etc fromthe airdata sensor input. These parameters are used by the control laws to stabilise the aircraftand to provide the required uniform handling qualities over the complete flight envelope. Thealgorithm is provided by the Control Law Design Team and coded by the Software Design Groupof Software House, ADA, Bangalore, in Ada language. The Independent Verification and ValidationGroup is responsible for ensuring that the software is bug-free and certifiable. A non-real time(NRT) test methodology has been developed in-house to stress test the onboard software. Thispaper gives an overview of the methodology used to carry out the NRT test of the airdataalgorithm and some of the testing experiences