Maneuverability and envelope protection in the prevention of aircraft loss of control

Loss-of-Control (LOC) is a major factor in fatal aircraft accidents. Although definitions of LOC remain vague in analytical terms, it is generally associated with a diminished capability of the pilot maneuver the aircraft — whether due to impairment of the aircraft or its entry into an unfavorable flight regime. Maneuver performance is usually assessed by evaluating an aircraft's ability to transition between desired steady state conditions such as wings level climb, descent, or coordinated turns. We show that even when a sufficient set of steady motions exist, the ability to regulate around them or transition between them can be difficult and non-intuitive, particularly for impaired aircraft. We examine the impact of control constraints, including those induced by actuator impairment, on the ability to prevent envelope departure and to maneuver within it. Safe set theory can be used as a basis for design of envelope protection systems. Higher dimensional safe sets are difficult to compute and visualize. For the full conventional longitudinal dynamics we present an analytic solution to a Hamiltonian which specifies the optimal safety critical control. We then use this expression in a numerical level set framework to compute four dimensional safe sets. Examples are provided using NASA's Generic Transport Model (GTM).