Initial Control Strategies for Conflicting Automatic Safety Systems in General Aviation

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Despite improvements in technology and safety systems, general aviation remains a relatively unsafe method of travel. According to 2019 US government statistics, Controlled Flight Into Terrain (CFIT) and Loss of Control Inflight (LOC-I) are the top two contributors for aircraft total loses and number of fatalities in general aviation. Fortunately, automatic safety systems which have the potential to decrease terrain collision accidents have been recently introduced into production as are automatic methods to avoid aerodynamic stall and other precursors to loss of control accidents. However, the union of these systems into a single control mechanism carries as-of-yet unquantified risk and potential for emergent or undesired behavior. Therefore, the research presented in this paper focuses on potential control strategies for combining automatic terrain avoidance and automatically securing controlled flight which maximizes certain desirable characteristics. This work presents initial analyses of conflicting safety constraints and architectural choices, and their impacts on the overall safety of a fixed-wing general aviation aircraft. The primary interest of this paper is to address the sequence of states and control inputs in which both safety systems request control of the aircraft concurrently leading to a conflict compromising the vehicle's safety and will evaluate the benefits and drawbacks of using specific switching strategies and control blending. After the initial phase of identifying relevant cases of conflicts, we analyze those cases to show the effectiveness of a mitigation approach based on switched-system control. The paper will also provide data in order to direct system designers as to the best approach to solve these types of problems given their individual set of requirements. The study is conducted in a realtime six degree of freedom (6DoF) flight simulation using a Cessna 172 aircraft model.