With the January 1, 2020, deadline for ADS-B out certification drawing near for aircraft flying in U.S. airspace that currently requires a Mode-C transponder, the FAA says pilots will be required before takeoff to assess how well their position-reporting avionics will perform along their filed flight plan route. The agency is specifically targeting GPS receivers that are not WAAS compatible.
The agency says pilots can use a service availability prediction tool (SAPT) to verify their GPS receivers meet the navigation integrity category (NIC) performance requirements used to define the accuracy of that position reporting equipment. NIC is the containment radius around an aircraft’s reported position which must be accurate within less than 0.2 nm of the airplane’s actual position. Using the SAPT creates a record of the check. Pilots should also refrain from checking GPS availability more than 24 hours prior to departure.
If the pilots receive a satisfactory prediction, the flight is good to go. Once the aircraft is airborne, pilots will not be held accountable if the GPS status changes, such as with an unexpected government interference test or a weather diversion that requires aircraft to enter an area of GPS unreliability.