Flight Test Results for an Experimental GPS C/A-code Receiver in a General Aviation Aircraft*

Abstract

This paper describes the design and flight test results of an experimental Global Positioning System receiver installed in a general aviation aircraft. These tests were part of a GPS test and evaluation project conducted for the Federal Aviation Administration by M.I.T. Lincoln Laboratory. The purpose of the project was to design a GPS C/A-code receiver that: 1) meets the current FAA requirements for two-dimensional area navigation (RNAV) systems, 2) employs techniques which could potentially lead to low-cost commercial avionics, and 3) is operationally compatible with existing ATC procedures and aircrew practices.Novel features of the design are: 1) the use of a dual-channel CA-code receiver, and 2) the tracking of all visible satellites in view rather than a minimum set of four satellites. The system employs two DEC LSI-11123 computers, one to perform position fixing and receiver control, and the other to perform navigation and data recording tasks. Pilot displays include a conventional course deviation indicator (CDI), omni-bearing selector COBS), and intelligent control and display unit (CDU).The GPS receiver was flight tested at a large urban airport, at several small general aviation airports, and over mountainous terrain. The horizontal system accuracy during typical aircraft flight profiles was measured to be 333 feet (95% confidence). This level of accuracy meets the FAA's current accuracy requirements for two-dimensional area navigation systems and is consistent with future navigational accuracy requirements.