Safety Analysis for Icing Aircraft during Landing Phase Based on Reachability Analysis

Icing is one of the leading causes of fatal aircraft accidents worldwide. Encountering icing conditions, dynamic characteristics of the aircraft will be damaged, thereby greatly affecting flight safety. Research on real-time estimations of the safety envelope under icing conditions is critical to improve flight safety. In order to determine the safety envelope, the reachability analysis based on the level set method is presented. The reachable set is obtained via computing the Hamilton-Jacobi partial differential equation (HJPDE), which is based on optimal control and is used in the landing phase of an aircraft. The results show that icing will shrink the safety envelope. Particularly under severe icing conditions, the stall speed of the aircraft will increase, and dynamic behavior will be more sensitive. A slight change of command by the pilot may contribute to the flight state moving outside the safety envelope. Furthermore, the effect of flap deflection was considered, which positively impacts the expanding safety envelope during the landing phase. Finally, a maneuvering coping strategy based on safety envelope is proposed. Examples are provided using the NASA’s generic transport model (GTM), and the results can be applied to flight safety risk assessment, providing theoretical guidance for the design of envelope protection systems.