type of automated station has different levels of approval  as outlined in individual OpSpecs. Ceiling and visibility  reports given by the tower with the departure information  are always considered official weather, and RVR reports are  typically the controlling visibility reference.  ATIS is another valuable tool for gaining weather  information. ATIS is available at most airports that have an  operating control tower, which means the reports on the  ATIS frequency are only available during the regular hours  of tower operation. At some airports that operate part-time  towers, ASOS/AWSS information is broadcast over the  ATIS frequency when the tower is closed. This service is  available only at those airports that have both an ASOS/  AWSS on the field and an ATIS-ASOS/AWSS interface switch  installed in the tower.  Each ATIS report includes crucial information about  runways and instrument approaches in use, specific  outages, and current weather conditions including  visibility. Visibility is reported in statute miles and may  be omitted if the visibility is greater than five miles. ATIS  weather information comes from a variety of sources  depending on the particular airport and the equipment  installed there. The reported weather may come from a  manual weather observer, weather instruments located  in the tower, or from automated weather stations. This  information, no matter the origin, must be from NWS  approved weather sources for it to be used in the ATIS  report.  The digital ATIS (D-ATIS) is an alternative method of  receiving ATIS reports. The service provides text messages  to aircraft, airlines, and other users outside the standard  reception range of conventional ATIS via landline and data  link communications to the flight deck. Aircraft equipped  with data link services are capable of receiving ATIS  information over their Aircraft Communications Addressing  and Reporting System (ACARS) unit. This allows the pilots to  read and print out the ATIS report inside the aircraft, thereby  increasing report accuracy and decreasing pilot workload.  Also, the service provides a computer-synthesized voice  message that can be transmitted to all aircraft within  range of existing transmitters. The Terminal Data Link  System (TDLS) D-ATIS application uses weather inputs  from local automated weather sources or manually entered  meteorological data together with preprogrammed menus  to provide standard information to users. Airports with  D-ATIS capability are listed in the CS.  The use of the aforementioned visibility reports and  weather services are not limited for Part 91 operators.  Part 121 and 135 operators are bound by their individual  OpSpecs documents and are required to use weather  reports that come from the NWS or other approved  sources. While every operator’s specifications are  individually tailored, most operators are required to use  ATIS, RVR reports, and selected reports from automated  weather stations. All reports coming from an AWOS-3  station are usable for Part 121 and Part 135 operators. Each  AWOS and ASOS/AWSS offer a wide variety of capabilities  and progressively broader weather reports. Automated  systems typically transmit weather every one to two  minutes so the most up-to-date weather information is  constantly broadcast. Basic AWOS includes only altimeter  setting, wind speed, wind direction, temperature, and dew  point information. More advanced systems, such as the  ASOS/AWSS and AWOS-3, are able to provide additional  information, such as wind speed, wind gust, wind direction,  variable wind direction, temperature, dew point, altimeter  setting, and density altitude. ASOS/AWSS stations providing  service levels A or B also report RVR. The specific type  of equipment found at a given facility is listed in the CS.  [Figure 1-12]  These systems are installed and maintained at airports  across the United States by both government (FAA and  National Weather Service (NWS)) and private entities. They  are relatively inexpensive to operate because they require  no outside observer, and they provide invaluable weather  information for airports without operating control towers.  [Figure 1-11]  An automated weather system consists of any of the  automated weather sensor platforms that collect weather  data at airports and disseminate the weather information  via radio and/or landline. The systems consist of the ASOS/  Automated Weather Sensor System (AWSS) and the AWOS.  Automatic Terminal Information Service (ATIS)  Automated Weather Systems  Digital Automatic Terminal Information Service  (D-ATIS)  1-12  Figure 1-12. CS entry for an AWOS station.  SAMPLE NOT FOR ACTUAL USE WEATHER DATA SOURCES: AWOS-3 119.675 (704) 735-6954.  AWOS/ASOS/AWSS information 