Real Time Simulation of a Low Cost GPS Navigator for Nonprecision Approaches

Abstract

This paper describes a real time simulation designed to evaluate the flyability of a low‐cost GPS navigator to be used by general aviation. The performance of such a GPS navigator may be degraded by satellite shielding during aircraft maneuvers associated with a nonprecision approach. Furthermore, the Department of Defense is proposing to reduce the navigation accuracy available to civil users of the GPS military satellite system. These concerns about the flyability of a low‐cost GPS navigator have motivated the development of a real time simulation in which a human pilot flies a general aviation trainer along an approach course guided by a computer simulated GPS navigation algorithm. By including the pilot and aircraft response characteristics, this simulation provides a direct comparison of the operational performance of a proposed low‐cost GPS navigator with the present VOR/DME system. Results of test pilots flying a simulated nonprecision approach procedure are given for VOR/DME and a low‐cost GPS navigator with errors due to satellite shielding and a hypothetical intentional degradation of GPS signals. These results indicate that the operational performance characteristics of the low‐cost GPS navigator are noticeably different from VOR navigation and may require different flying techniques as a result. Pilots may be confused by false wind indications due to intentional degradation of GPS signals. An unstable interaction between pilot and navigation may occur if more than one low‐elevation satellite can be shielded by turning the aircraft in different directions. The simulation described herein provides an experimental tool for investigating further the reaction of GA pilots to intentional degradation of GPS navigation accuracy and methods for reducing errors due to satellite shielding.