CHAPTER 12:  GPS INTEGRITY AND CIVIL AVIATION

12.1 INTRODUCTION

The civil aviation view of GPS is significantly different than that of most military

users. The primary technical difference is that SPS C/A code will be the only GPS

signal available to most civil aviation users.  Therefore, the civil aviation user must

consider the reduced accuracy and statistical accuracy variations induced by SA. 

Consequently, civilian users are planning to use augmentations, for example,

differential GPS, to improve the accuracy and availability of the SPS signals.

The primary difference in use of GPS is that civil aviation will use GPS almost

exclusively for navigation and position reporting where safety of life is of

tantamount importance. Therefore, integrity of the position solution is also of

tantamount importance.  Military users take a broader view of GPS as a force

enhancement that will include peacetime as well as wartime operations and

manned as well as unmanned missions.  Therefore, military integrity requirements

can vary widely depending on the mission, and can range, for example, from the

extreme concern of safety of life for manned peacetime operations to lesser

requirements for weapon effectiveness in a war fighting environment.

Civil aviation also views GPS as a major component of a Global Navigation Satellite

System (GNSS).  The GNSS concept also includes the Russian Global Orbiting

Navigation Satellite System (GLONASS), geostationary satellites broadcasting

GPS  and/or GLONASS like signals, and a possible international civil navigation

satellite system.  In this respect, it is likely that the civil aviation community will field

systems that accept signals from more than one component of the GNSS to improve

the overall accuracy, availability, and integrity of the civil positioning solution.

GPS and GNSS equipment for civil aviation will range from minimum capability

stand alone receivers for general aviation users, to sophisticated integrated

navigation systems for commercial users.

The primary benefit of GPS and GNSS from a Civil Aviation Authority (CAA) point 

of view is that GPS/GNSS has the potential to replace many existing ground based

radio navigation aids or obviate the need to procure new systems, thereby reducing

the cost of maintaining or acquiring these systems.  This is especially true for

developing nations that do not have an extensive navaid infrastructure, and who

could instead provide a regional integrity supplement to GPS (or GNSS) at a much

lower cost than a traditional VOR navaid infrastructure.

The primary benefits of GPS and GNSS from a user point of view are potential fuel

(cost) savings from more direct routing, improved (global) navigational coverage,

and the potential to replace multiple navigation systems with a multi use system. 

The primary concerns stem from the safety of life issue and the fact that GPS

signal failures can affect large areas and consequently large numbers of aircraft

simultaneously.

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