Plain English Meaning

It was a deliberate fuzzing of GPS accuracy for non-military users. The government built it into GPS to keep enemies from getting pinpoint accuracy, then switched it off in 2000 so civilian GPS — including aviation receivers — could be much more accurate.

Full Definition

Selective Availability (SA) was a U.S. Department of Defense feature that intentionally degraded the accuracy of civilian GPS signals by introducing small, controlled errors into the satellite timing and position data. It was used to prevent adversaries from exploiting the full precision of GPS for military purposes. SA was set to zero (turned off) on May 1, 2000, and the capability to reintroduce it was permanently removed from later GPS satellites.

Context Anchor

Seen in discussions of GPS accuracy, especially when comparing older GPS limitations with current GPS .