Almanac data stored in the receivers of some early Garmin 'Flybuddy' GPS units has led to degraded operation. Affected units, according to a service advisory from Garmin, include all Model 819 and Model 820 Flybuddy GPS units and Model 2001/2101 systems with TSO-C115b GPS sensors. The company noted that Model 2001/2101 systems with later TSO-C129 GPS sensors are not affected by the problem, which started on August 17. Because the almanac data reached the end of its programmed "GPS week," service was interrupted or degraded. Symptoms included the following status indications; no-fix; 2-D fix only; brief periods of 3-D fix; and combinations of all three symptoms. Garmin wrote it has determined that the units cannot recover normal operations on their own, and the company is in touch with the third-party supplier of the GPS sensors to resolve the issue and restore functionality. The company expects to post information on the situation within one or two weeks on its website garmin.com.