PRIMARY MEANS OF NAVIGATION
A means of navigation which satisfies the necessary levels of .accuracy and integrity for a particular area, route, procedure or operation. The failure of a “Primary Means” of navigation may result in, or require reversion to a “non-normal” means of navigation, or an alternate level of RNP. Qualification as a “primary means” of navigation typically requires that ANP/EPU be less than RNP for 99.99% of the time.