Optimum flight trajectories for terrain collision avoidance
Creators: name: Sharma, Tapan
Publisher: name: RMIT University
Year: 2024

description: Ground Proximity Warning Systems (GPWS), Enhanced Ground Proximity Warning Sensors (EGPWS) and Terrain Awareness Systems (TAWS) have been developed to aid in the reduction of aircraft ground collisions. They are devices which provide pilots with an aural warning signal of proximity of terrain. These systems make use of a downward looking sensor which senses the proximity of oncoming terrain. Certainly these warning devices are beneficial if the pilot reacts to them but they do not assist in improving the situation awareness of the flight crew or what action to take to avoid a collision.<br>The implementation of such systems has reduced aircraft accidents caused by Controlled Flight into Terrain (CFIT) however it has not been eliminated. Thus it is necessary for a new system to be developed, that would not only act like a warning, but would also be capable of assisting the pilot by providing him with safe escape trajectories in a situation which could eventuate into a CAT accident. Pilots usually conduct a pull- up manoeuvre when in ground proximity to increase altitude. This is a logical response but in high mountainous terrain, this manoeuvre may still result in a collision. Furthermore, the sudden pull up manoeuvre could cause the aircraft to exceed its aerodynamics, structural and propulsion limitations. For example load factor. <br>Hence, the primary aim of this research is to develop a methodology utilizing the availability of a three dimensional digital terrain topology database and aircraft position to compute safe escape trajectories in both vertical and lateral directions. The aircraft model used was a Phantom F4. The objective of this thesis is to prove that flying around a terrain can provide the pilot a better chance of survival than by conducting the regular pull up manoeuvre in case there is not adequate time. To add more value to this study, two more objective functions have been added, minimum time and minimum clearance from the terrain. In the former case, the aircraft has to clear the terrain in the least possible time whilst in the latter case; the aircraft has to clear the terrain by flying close to the terrain at a specified clearance. The two scenarios have been selected as military aircraft are most often involved in Terrain Avoidance (TA) and Terrain Following (TF) operations to prevent them from being exposed to enemy fire. However emphasis is given more on avoiding collision rather than planning a collision avoidance strategy. <br>The second part of this investigation involves a sensitivity analysis of instrument errors on the ability to fly an optimal escape trajectory. Instrumental errors are always present and should be considered in any flight simulation to determine how practical the methodology is. To investigate the extent of influence of instrumental errors, there is a need to conduct a sensitivity analysis which is presented. The sensitivity study involves consideration of various scenarios in which the aircraft is required to fly an optimal flight trajectory out of collision. The principal reason for such analysis Is to determine the sensitivity of the optimal escape trajectory solution subjected to instrument errors. <br>Snopt and Direct software were used extensively in Matlab environment version 7 for all the analytical work conducted for this thesis. The three dimensional terrains were initially generated via using functions such as cylinders, cones, etc. Subsequently the more complicated shape of the terrains were generated in Terrain Generator which was exported and converted to Direct format file using B-Splines function in Matlab. Further details pertaining to generation of results are provided. <br>The results obtained in this thesis show that generation of safe aircraft trajectories in a three dimensional digital terrain topology are possible. Although the equations of motion were based on three degrees of freedom, there were limitations added on the dynamics of the aircraft to make it realistic. The ability to use different terrains for modelling also proves that the method is versatile. Finally investigation of the sensitivity analysis shows the ability to counter act the errors in navigational instruments of the aircraft. <br>