Global service availability on a day where the worst case satellite is removed from

service is 99.85%; the associated worst case regional service availability is 97.63%.

The resulting 30 day service availability values do not change much between the best

and worst cases, with the worst case value being 99.98%.

Table 6 5.  Example of 30 Day Global Service Availability

 without Component Failure

Ops Scenario Condition

Best Case

Average Case

Worst Case

3 Days   1 Satellite Down

 99.98%

 99.93%

 99.85%

27 Days   No Satellites Down

100.00%

100.00%

100.00%

Average Daily Availability

 99.99%

 99.99%

 99.98%

6.1.4  Service Reliability Characteristics

This section defines conservative expectations for GPS service reliability performance.

These expectations are based upon observed accuracy characteristics, the GPS

service failure history to date, long term failure rate projections, and current system

failure response capabilities.  The user is provided with information which indicates

expected failure rates and their effects on a global and regional basis.

6.1.4.1  Service Reliability Standards

GPS service will be provided in accordance with the reliability standards presented in

Table 6 6.

Table 6 6.  Service Reliability Standards

Service Reliability

Conditions and Constraints

 99.97% global

  Conditioned on coverage and service availability standards

average

  Standard based on a measurement interval of one year; average of

daily values over the globe

  Standard predicated on a maximum of 18 hours of major service failure

behavior over the sample interval

 99.79% single point

  Conditioned on coverage and service availability standards

average

  Standard based on a measurement interval of one year; average of

daily values from the worst case point on the globe

  Standard based on a maximum of 18 hours of major service failure

behavior over the sample interval

6 8