WAAS PRN 135 Satellite Ceases Broadcast
December 17, 2010The Federal Aviation Administration announced that the Wide Area Augmentation System (WAAS) Intelsat CRW geostationary (GEO) satellite PRN 135 has ceased broadcasting the WAAS signal as of December 16, 2010. The deterioration of the satellite’s ability to remain stable over the past few days caused intermittent data link disruptions that rendered the satellite unreliable for further data transmissions. The FAA’s mitigation plan to activate another satellite in November 2010 was successful and the new GEO satellite, Inmarsat AMR (PRN 133), has been transmitting the WAAS signal in addition to the Telesat CRE GEO.
December 16, 2010 WAAS GEO Coverage Map (Courtesy: FAA)
According to the announcement, sixteen airports north of a line from 70N150W and 64N164W in northwest Alaska are affected by the failure. Only one of the 16 airports located in the affected area has published LPV approaches, and that airport is NOTAMed out for any WAAS procedures. Users of these 16 airports will continue to fly the existing lateral navigation (LNAV) procedures and are required to confirm that GPS receiver autonomous integrity monitoring (RAIM) will be available for all flights during planning. Please refer to Anchorage Center NOTAMS for specific guidance.
The WAAS broadcast over a large portion of the rest of Alaska will now be provided by a single GEO. WAAS users in this area may experience temporary service outages due to lack of redundant GEO signals. These outages will occur during a switch between the primary and backup GEO Uplink System (GUS) stations. These switchovers will occur approximately 4 – 5 times a month and it may take up to 5 minutes to fully restore LPV service after an occurrence.
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