December 28, 2010
By Dan Namowitz
The satellite providing Wide Area Augmentation System (WAAS) signals that began to malfunction this spring has ceased broadcasting, the FAA announced. AOPA reported on the satellite’s technical problems on April 13.
The FAA described the operational impacts of the discontinuation on routings in northwestern Alaska, and the availability of alternate routes, in this Oct. 20 letter to Heidi Williams, AOPA senior director of airspace and modernization.
The outage also affects minimums for two lateral precision with vertical guidance (LPV) approaches: the RNAV (GPS) RWY 7 approach at Wiley Post-Will Rogers Memorial Airport in Barrow and the RNAV (GPS) RWY 9 approach at the Ralph Wien Memorial Airport in Kotzebue.
“The Wide Area Augmentation System (WAAS) Intelsat CRW geostationary (GEO) satellite has ceased broadcasting the WAAS signal as of today. 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, has been transmitting the WAAS signal in addition to the Telesat CRE GEO,” said the FAA in a Dec. 16 news release on its Navigation Services Web page.
Of the 16 airports in northwest Alaska affected by the failure, two have published LPV approaches, and those airports are under a notice to airmen (NOTAM) barring 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,” the FAA said.
WAAS broadcasts over much of the rest of Alaska are now provided by one GEO satellite.
“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 four [to] five times a month, and it may take up to five minutes to fully restore LPV service after an occurrence,” the FAA cautioned.
Dan Namowitz is an aviation writer and flight instructor. He has been a pilot since 1985 and an instructor since 1990.
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