Chart Supplements (formerly known as "The Airport/Facility Directory" in the United States) contain additional information about airports, seaplane bases, and other aviation facilities which may not be published on aviation charts to conserve space.
Chart Supplements are a listing of additional data about airports, seaplane bases, heliports, NAVAIDs, communications data, weather data sources, and other information which may be useful to aviators in planning flights.
Chart Supplements generally include data that cannot be readily depicted in graphic form, such as airport hours of operation / attended hours, types of fuel available, runway data (surface type, arresting gear), lighting codes, etc.
US FAA Chart Supplements also include the Aeronautical Chart Bulletin, which describes major changes, in aeronautical information that have occurred since the last publication date of associated VFR Sectionals, Terminal Area Charts, and Helicopter Route Charts.
They also include telephone numbers for selected major facilities (Centers and TRACONs).