Landing Site Reachability in a Forced Landing of Unmanned Aircraft in Wind

Autonomous contingency management systems, such as a forced-landing system, which reacts appropriately to an engine failure, are important for the safe operation of unmanned aircraft systems. This paper details a method to ascertain the reachability of any possible emergency landing site for a forced landing in steady uniform wind conditions. With knowledge of the aircraft's state, such as speed, heading, location, and orientation of a landing site, a method to calculate a minimum height loss path is developed based on aircraft glide performance. Wind direction and speed are taken into account using a trochoidal approach by defining the minimum height loss turn path. To facilitate real-time implementation, simplified gliding equations are developed without accuracy loss. The reachability of each site can be calculated as well as how much safety margin an aircraft would have. This method is generic and could also provide decision support for human pilots in forced-landing situations. Two types of aircraft, the Airbus A320-400 and the Cessna 172, have been investigated to demonstrate the usefulness of the method, using Monte Carlo simulations in a synthetic X-Plane simulation environment, to demonstrate the performance and effectiveness of the proposed approaches.