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Selective Availability

Selective Availability (SA) was an intentional degradation of public GPS signals implemented for national security reasons.

In May 2000, at the direction of President Bill Clinton, the U.S government discontinued its use of Selective Availability in order to make GPS more responsive to civil and commercial users worldwide.

The United States has no intent to ever use Selective Availability again.

In September 2007, the U.S. government announced its decision to procure the future generation of GPS satellites, known as GPS III, without the SA feature. Doing this will make the policy decision of 2000 permanent and eliminate a source of uncertainty in GPS performance that had been of concern to civil GPS users worldwide.

The Interagency GPS Executive Board (IGEB) issued the following public statements to reaffirm the continued availability and accuracy of civil GPS following the September 11, 2001, terrorist attacks and the subsequent wars in Iraq and Afghanistan. The IGEB was the predecessor to today's National Executive Committee for Space-Based PNT.

U.S. Policy Statement Regarding Civil GPS Availability
March 21, 2003
The United States Government recognizes that GPS plays a key role around the world as part of the global information infrastructure and takes seriously the responsibility to provide the best possible service to civil and commercial users worldwide. This is as true in times of conflict as it is in times of peace.

The U.S. Government also maintains the capability to prevent hostile use of GPS and its augmentations while retaining a military advantage in a theater of operations without disrupting or degrading civilian uses outside the theater of operations.

We believe we can ensure that GPS continues to be available as an invaluable global utility at all time, while at the same time, protecting U.S. and coalition security requirements.

Special Notice
September 17, 2001
GPS Selective Availability (SA) has not been used since its deactivation by the President on May 1, 2000. At that time, the United States Government stated that it has no intent to ever use SA again. There has been no change in this policy.

It is important to note that, pursuant to both the United States GPS Policy and the Federal Radionavigation Plan, the Global Positioning System and all other federally provided radionavigation systems are responsive to the National Command Authorities.

For the most current information on the operational status of GPS and GPS-related services, please refer to the U.S. Coast Guard Navigation Center, which is responsible for disseminating operational GPS information to the civilian user community.

Frequently Asked Questions About Selective Availability

Selective Availability ended a few minutes past midnight EDT after the end of May 1, 2000. The change occurred simultaneously across the entire satellite constellation.

The United States has no intent to ever use SA again. To ensure that potential adversaries do not use GPS, the military is dedicated to the development and deployment of regional denial capabilities in lieu of global degradation.

No. Existing GPS receivers around the world should be getting the higher accuracy right now without any modifications.

It depends on your specific user requirements. If you are using GPS for safety-critical navigation, you will still need to use the Coast Guard DGPS or Nationwide DGPS to get the higher accuracy (1-3 meter) and the integrity monitoring/warning service. If you are a surveyor requiring sub-meter positioning, you will still need some form of DGPS to achieve that level of precision.

On the other hand, if you are a trucking company using GPS to track and manage assets, the < 20 meter accuracy now available from the basic civil signal may be sufficient to meet your needs without DGPS augmentations.

Yes. The U.S. Coast Guard will continue to run the maritime DGPS network to provide the higher accuracy and integrity monitoring/warning service required for safety-critical navigation. In fact, efforts are currently under way to expand the Coast Guard DGPS network across the continental United States to provide the same GPS augmentation service to terrestrial users on railroads and highways. The expanded network is known as the Nationwide DGPS, or NDGPS, service.

No. There should not be much change in the accuracy of DGPS. However, DGPS corrections may not need to be broadcast as frequently any more. As a result, we may see future commercial DGPS services that use less radio bandwidth and thus cost less to the end user.

No. You have been misinformed. Selective Availability was a global degradation of the GPS service. It could not be applied on a regional basis. By turning it off, the President immediately improved GPS accuracy for the entire world. The United States has no intention of reactivating SA ever again.

Users in the U.S. and the rest of the world should now be experiencing the same basic GPS accuracy of 10-20 meters or better.

In theory, civil receivers should now match the accuracy of PPS receivers under normal circumstances. We are in the process of collecting data to verify whether this is true. PPS still gives advantages to the military beyond accuracy.

On October 4, 2001, the agencies of the Interagency GPS Executive Board finalized and released the revised GPS Standard Positioning Service (SPS) Performance Standard, taking into account the new levels of performance achievable without SA.

The SPS Performance Standard differs from the previous SPS Signal Specification in several ways. Rather than focus on the accuracy levels achievable on the ground, the document provides guarantees on the characteristics of the signal in space and the satellite constellation. This allows end users in different parts of the world to make more accurate predictions of GPS performance in their particular location, taking into account regional effects of the atmosphere and satellite geometry, as well as the effects of their particular user equipment.