Analyze the Mode Transition Logic of Automatic Flight Control System using Semi-Formal Approach

Autopilot system is a highly critical avionics system in modern aircraft as it steers the aircraft automatically. The autopilot is a highly complex system driven by a complex logic and is one of the major reasons for the accidents in automated airliner. The autopilot logic consists of the mode-transition logic which in automated mode steers the aircraft based on the aircraft aerodynamics. In the automated mode the correct and efficient working of the modetransition is highly critical; hence a high assurance approach is required to analyze the logic for its functionality and performance. In this paper, we present a semi-formal method based approach to analyze and validate the Mode-Transition Logic (MTL) for an indigenously developed commercial aircraft in the vertical and lateral directions. The MTL is analyzed and validated for its correct, complete, and reliable functionality and operation using Stateflow. The modeled MTL logic is validated for the allowed transitions based on the input combinations against the requirements for functionality and safety. The outcome of the approach shows encouraging results with respect to assurance in functionality, performance and safety in comparison to the conventional manual approach of testing. Similar semiformal based approach can be used to reduce the design effort in the design and development of complex system designs as compared to the manual analysis.