As part of the pre-flight planning procedure, a Pilot should check the availability of the GNSS satellites through NOTAMs, GNSS outage advisories, such as NANUs, or consulting their operator's procedures, so he/she can be aware in advance of whether the constellation and augmentation will be available at all stages of the flight, but especially for the destination airfield and alternate at the estimated time of arrival.

An instrument approach procedure, based on GNSS guidance and integrity information for lateral and/or vertical navigation, requires that the constellation and associated augmentation/integrity services are available at the time that approach is initiated.