Recovery Autopilot Analysis for a General Aviation Ground Collision Avoidance System

General aviation, the mode of air travel typified by small personal aircraft, accounts for roughly 19 of every 20 fatalities every year in the US. However, recent technological solutions are becoming available which may bring the total number of fatalities in general aviation down considerably. Potentially the most effective of these solutions is the Ground Collision Avoidance System or GCAS. GCAS avoids ground collision in a large number of cases: pilot error, disorientation, and temporary incapacitation. However, GCAS does not yet exist for general aviation, despite it being a field that would widely benefit from it's implementation. In response to this reality, GCAS development for general aviation has begun. This paper describes the design and verification of a GCAS controller on a simulated Cessna 172 aircraft. The GCAS controller provides the ability for the aircraft to automatically avoid ter-rain and is an important step in the initial phases of GCAS design. Considerations for the design of the controller's lateral and longitudinal axes are provided along with discussions on the overall controller structure. Controller modes and limiters have been designed and described to ensure safe operation of the controller, along with considerations for transient switching effects. Analysis of controller response along with verification of mode and limiter operation are provided. Finally, a comparison between the trajectory generated by the GCAS controller and one predicted by the GCAS system are included. With these sections, this paper provides important considerations on the initial stages of GCAS design for general aviation, and the beginning of safety assurance for GA.