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79 Altimeter Setting: The local barometric pressure in inches of mercury, used to calibrate the altimeter in an aircraft for local conditions. Automatic Terminal Information System (ATIS): A continuous broadcast of recorded aeronautical information essential information, such as current weather, active runways, available approaches, and any other information required by the pilots, such as important Notices to Airmen (NOTAMs). Aviation Selected Special Weather Report (SPECI): A special weather report issued when there is significant deterioration or improvement in airport weather conditions, such as significant changes of surface winds, visibility, cloud base height, and occurrence of severe weather. The format of the SPECI report is similar to that of the METAR, and the elements used have the same meaning. Benefit-Cost Analysis (BCA): An accounting process quantifying and comparing the antici- pated benefits of a project to the construction and operating costs of a project. Ceilometer: A device that uses a laser or other light source to determine the height of a cloud ceiling or cloud base. Ceilometers can also be used to measure the aerosol concentration within the atmosphere. Direct User Access Terminal Service (DUATS): A discontinued weather information and flight plan processing service contracted by the FAA for use by U.S. pilots. The DUAT Ser- vice was a telephone- and Internet-based system that allowed the pilot to use a personal computer for access to an FAA database to obtain weather and aeronautical information and to file, amend, and cancel domestic IFR and VFR flight plans. The service was discontinued on May 16, 2018. Meteorological Terminal Aviation Routine Weather Report (METAR): A routine weather report issued at hourly or half-hourly intervals. It is a description of the meteorological elements observed at an airport at a specific time. National Airspace Data Interchange Network (NADIN): The FAA commissioned the NADIN II on March 31, 1995. The high-speed data communications system was designed to improve the controllersâ ability to pass information to pilots and to reduce annual tele- communications costs. National Plan of Integrated Airport Systems (NPIAS): Includes all commercial service airports, all reliever airports, and selected publicly owned general aviation airports. Glossary
80 Airport Surface Weather Observation Options for General Aviation Airports Octant: A circular sector obtained by division of the full circle into 8 equal parts. It is a sector with a central angle of 45Â°. Terminal Aerodrome Forecast (TAF): A concise statement of the expected meteorological conditions at an airport during a specified period (usually 24 hours). WXBrief: The service provided by FAA and NWS for disseminating official weather informa- tion to pilots via telephone or a dedicated web page.