Integrated System for Automatic Landing Using Differential GPS and Inertial Measurement Unit

Abstract

GPS-receivers have accuracy problems in high precision flight gui­dance applications. In dynamic flight maneuvers they show not only operational problems due to satellite masking but also a reduction in accuracy in accelerated flight and turn flight.

In the presented “Integrated System” those problems are solved by integrating GPS in differential mode with inertial measurment sensors into a hybrid system. This integrated system computes a high precise position, flight path and attitude information of a moving platform e.g. an aircraft.

The error behaviour in stationary and in dynamic applications is ex­plained. From the error behaviour a system concept of a hybrid Inte­grated Flight Guidance System is derived.

The position information, estimated in real-time, is used for a flight guidance value generator. These informations are fed to a flight di­rector instrument in the cockpit, which is used by the pilot for manual flight or is fed to an autopilot for automatic flight including automatic approach and touch down.

The system fulfills extreme accuracy requirements and can be used in approach and landing up to ICAO (International Civil Aviation Organi­zation) CAT III. It allows to perform landings even in bad weather conditions. As the integrated system is space based, it computes a landing aid which allows landing at any airfield, not equipped with con­ventional Instrument Landing System or Microwave Landing System.

In July 1989 the worldwide first automatic landing, using the presen­ted system, based on GPS has been performed by the Institute for Guidance and Control of the Technical University of Braunschweig.

The suitability of the concept (Kalman Filter coupling GPS and inertial measurement units (IMU)), for flight path guidance and the accuracy of position finding (better than 1.3 m) will be presented by means of flight tests in a commuter aircraft (DORNIER DO 128) and also by si­mulator results. An inflight comparison of a reference Instrument Landing System with the Integrated System shows the accuracy.