Under certain conditions, the Garmin 400W/500W series units will not provide serial heading information to the L3 WX-500 Stormscope. Even if the WX-500 unit is wired for synchro heading, there may be issues with the WX-500, GDL-69 datalink, and crossfill between two Garmin units. Also, some issues have been encountered with the COM flip/flop key not switching between the active and standby frequencies. As of 8/20/07, Garmin plans to resolve these issue with the next software release. The software upgrade should be able to be completed at your local Garmin authorized facility.