VOLMET
VOLMET, or meteorological information for aircraft in flight, is the term applied to a worldwide network of radio stations that broadcast TAF, SIGMET and METAR reports on shortwave frequencies. In some countries, VOLMET stations broadcast on VHF frequencies too. Reports are sent using automated voice transmissions, in the upper sideband or J3E mode. As the name suggests, pilots on international air routes, such as North Atlantic Tracks, use these transmissions to determine what maneuvers to make to avoid severe storms or turbulence, as well as which procedures to use for descent, approach, and landing, such as a visual approach versus an instrument approach and the correct arrival procedure.
The VOLMET network divides the world into specific regions, and individual VOLMET stations in each region broadcast weather reports for specific groups of air terminals in their region at specific times, coordinating their transmission schedules so as not to interfere with one another. Schedules are determined in intervals of five minutes, with one VOLMET station in each region broadcasting reports for a fixed list of cities in each interval. These schedules repeat every hour.
