FAA: GPS Outage Won’t Count As ADS-B Violations


The FAA released a policy statement (PDF) last week assuring operators that “the FAA will not consider aircraft non-compliant with the ADS-B Out rule during periods of GPS performance degradation that are outside the operator’s control. The circumstances are identified in the policy and are valid provided the operator has exercised appropriate due diligence prior to conducting an operation.”

As long as operators exercise “due diligence” in determining GPS and, therefore, ADS-B Out coverage prior to launching, the FAA says it will not dock pilots who experience unexpected GPS glitches that affect the ADS-B system from providing a position solution. Similarly, the FAA says that pilots who are given a routing other than the one filed that results in ADS-B “failure” will not be violated.

The bulk of the FAA’s concern has to do with so-called SA-On or SA-Aware GPS units providing a position solution to the ADS-B network. The FAA notes that WAAS-enabled, complying GPS position sources, such as an IFR-approved GPS, are equivalent to radar in terms of position accuracy. 

Marc Cook
KITPLANES Editor in Chief Marc Cook has been in aviation journalism for more than 30 years. He is a 4000-hour instrument-rated, multi-engine pilot with experience in nearly 150 types. He’s completed two kit aircraft, an Aero Designs Pulsar XP and a Glasair Sportsman 2+2, and currently flies a 2002 GlaStar.

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  1. “The FAA notes that WAAS-enabled, complying GPS position sources, such as an IFR-approved GPS, are equivalent to radar in terms of position accuracy.”

    Right. As long as all of the apparatus is working. Satellites, sat receivers, navigators (“position resolvers”), position transmitters, position receivers.

    It takes as special kind of bureaucrat to characterize any of this as “surveillance.”
    Webster has a different opinion.

  2. From the FAA website

    • There are three common position sources in use for ADS-B:
    • GPS that behave as if Selective Availability (SA) is still active (SA-On);
    • GPS that behave as if SA has been deactivated (SA-Aware), and
    • GPS that have Satellite Based Augmentation System (SBAS) such as the U.S. Wide-Area
    Augmentation System (WAAS)
    • Selective Availability (SA) Impact
    • SA-On and SA-Aware GPS have been shown to have brief periods where they produce
    NIC and NACp below the rule performance requirements, particularly when there are a
    reduced number of GPS operational satellites.
    • This could have an impact on an operator’s ability to comply with the rule or gain access to
    rule airspace at desired times on desired routes.
    • Analysis has shown that SA-On GPS receivers will fail to achieve the NIC requirements with high
    availability (equal to or greater than 99.9% availability) under many expected GPS constellation
    • SA-Aware GPS receivers will have improved performance over SA-On and are likely to meet the
    NIC and NACp requirements when the GPS constellations has a large numbers of satellites
    • SBAS receivers use additional signals from geostationary satellites specifically designed
    for aviation use for improved availability and not affected by SA
    • SA-On and SA-Aware are widely used in current air transport aircraft
    • Operators must consider these characteristics and the impact on flight operations

    These SA Aware GPS receivers make up the bulk of airline fleet. These are second generation GPS navigators and have been in the fleet for years. Very few airliners have WAAS GPS sources. The FAA knows there are times the GPS satellite constellations are not in a position for these SA-ON and SA-Aware based GPS navigators to proper “see”. So, when the heavies end up in this position, they will get a “pass” instead of a violation.

    For us GA drivers, we MUST have an on-board WAAS GPS source to comply. No other options or choices. WAAS GPS source does not have the the problem with the GPS satellite constellation positioning. We bust ADS-B airspace through some GPS derived problem or equipment failure, we get violated.

    2020 will be an interesting aviation and political year.