Development of an Automatic Ground Collision Avoidance System Using a Digital Terrain Database

Several ground collision avoidance systems GCAS have been developed to warn the pilot of a potential collision with the terrain is some action is not taken. All current systems have shortcomings pertaining to the sensors that are used and the recovery maneuver that is flown. The USAF is evaluating the potential of digital terrain databases for onboard navigation and terrain avoidance in combat aircraft. The purpose of this thesis was to develop a control system for performing terrain avoidance using a simulated terrain database. This study was conducted for an F-16 aircraft in level flight at 0.6 Mach and sea level conditions. A state-space model of the aircraft and its flight control system was developed using aircraft control derivatives, an F-16 control law diagram, and traditional linearization techniques on the aircraft equations of motion. A control system for implementing terrain avoidance was derived based on the look-ahead capability of the terrain database. Control system response was evaluated using a simulated terrain obstacle and various look-ahead distances on the terrain database. Results indicated that a 1200 foot, or roughly 1.8 second, look-ahead distance provided good improvement in terrain avoidance capabilities for the F-16 compared to looking strictly downward from the aircraft for terrain information. Theses.