8.4.3 Every ASOS/AWSS will contain the follow-ing basic set of sensors.
8.4.3.1 Cloud height indicator (one or possibly three).
8.4.3.2 Visibility sensor (one or possibly three).
8.4.3.3 Precipitation identification sensor.
8.4.3.4 Freezing rain sensor.
8.4.3.5 Pressure sensors (two sensors at small airports; three sensors at large airports).
8.4.3.6 Ambient temperature/dew point temperature sensor.
8.4.3.7 Anemometer (wind direction and speed sensor).
8.4.3.8 Rainfall accumulation sensor.
8.4.4 The ASOS/AWSS data outlets include:
8.4.4.1 Those necessary for on.site airport users.
8.4.4.2 National communications networks.
8.4.4.3 Computer.generated voice (available through FAA radio broadcast to pilots and dial.in telephone line).
NOTE.
Wind direction broadcast over FAA radios is in reference to magnetic north.
8.5 A comparison of weather observing programs and the elements observed by each are in TBL GEN 3.5.3, Weather Observing Programs.
8.6 Service Standards. During 1995, a govern-ment/industry team worked to comprehensively reassess the requirements for surface observations at the nation’s airports. That work resulted in agreement on a set of service standards and the FAA and NWS ASOS sites to which the standards would apply. The term “Service Standards” refers to the level of detail in the weather observation. The service standards consist of four different levels of service (A, B, C, and D) as described below. Specific observational elements included in each service level are listed in TBL GEN 3.5.4, Weather Observation Service Standards.
8.6.1 Service Level D defines the minimum acceptable level of service. It is a completely automated service in which the ASOS/AWSS observation will constitute the entire observation; i.e., no additional weather information is added by a human observer. This service is referred to as a stand alone D site.
8.6.2 Service Level C is a service in which the human observer, usually an air traffic controller, augments or adds information to the automated observation. Service Level C also includes backup of ASOS/ AWSS elements in the event of an ASOS/AWSS malfunction or an unrepresentative ASOS/AWSS report.
8.6.3 In backup, the human observer inserts the correct or missing value for the automated ASOS/AWSS elements. This service is provided by air traffic controllers under the Limited Aviation Weather Reporting Station (LAWRS) process, FSS and NWS observers, and, at selected sites, Non.Federal Observation Program observers.
Two categories of airports require detail beyond Service Level C in order to enhance air traffic control efficiency and increase system capacity. Services at these airports are typically provided by contract weather observers, NWS observers, and, at some locations, FSS observers.
8.6.4 Service Level B is a service in which weather observations consist of all elements provided under Service Level C, plus augmentation of additional data beyond the capability of the ASOS/AWSS. This category of airports includes smaller hubs or airports special in other ways that have worse than average bad weather operations for thunderstorms and/or freezing/frozen precipitation, and/or that are remote airports.
8.6.5 Service Level A, the highest and most demanding category, includes all the data reported in Service Standard B, plus additional requirements as specified. Service Level A covers major aviation hubs and/or high volume traffic airports with average or worse weather.
TBL GEN 3.5.3
Weather Observing Programs
ElementReportedType Wind Visibility TemperatureDew Point Altimeter DensityAltimeter Cloud/Ceiling PrecipitationIdentification Thunderstorm/ Lightning PrecipitationOccurrence RainfallAccumulation Runway SurfaceCondition Freezing RainOccurrence Remarks
AWSS X X X X X X X X X X
ASOS X X X X X X X X X X
AWOS.A X
AWOS.A/V X X
AWOS.1 X X X X
AWOS.2 X X X X X
AWOS.3 X X X X X X
AWOS.3P X X X X X X X
AWOS.3T X X X X X X X
AWOS.3P/T X X X X X X X X
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