Users Advisory - DGPS

Differential GPS Equipment Generated Errors

The Coast Guard Navigation Information Service (NIS) recently received report of Differential GPS (DGPS) receivers apparently
ignoring the broadcast alarm which signals immediate discontinuation of a particularsatellite correction. In accordance with the
international and industry standards (RTCM SC104), the United States Coast Guard DGPS broadcast sets a satellite correction to
the defined "DO NOT USE" value of 10485.76 meters if broadcast integrity checks indicate there is a problem with the satellites
correction.

Reports indicate some users equipment does not properly recognize this "DO NOT USE" correction flag and instead erroneously
processes it as a correction. This can result in correction errors as large as 1500 meters, while the receiver is in the DGPS mode.
DGPS users should contact the manufacturer of their equipment immediately to determine if they require a receiver upgrade.

An error of this magnitude could result in some pretty serious navigation problems during night and inclement weather operations.