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NOTEWind
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 3.5-2, Weather Observing Programs.
8.6 Service Standards. During 1995, a government/
industry team worked to comprehensively
reassess the requirements for surface observations at
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GEN 3.5-27
15 MAR 07
Federal Aviation Administration Nineteenth Edition
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 3.5-3, 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 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
elements in the event of an ASOS malfunction or an
unrepresentative ASOS report.
8.6.3 In backup, the human observer inserts the
correct or missing value for the automated ASOS
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. 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.
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15 MAR 07
Nineteenth Edition Federal Aviation Administration
TBL GEN 3.5-2
Weather Observing Programs
Element Reported AWOS-A AWOS-1 AWOS-2 AWOS-3 ASOS MANUAL
Altimeter X X X X X X
Wind X X X X X
Temperature/Dew point X X X X X
Density altitude X X X X
Visibility X X X X
Clouds/Ceiling X X X
Precipitation X X
Remarks X X
TBL GEN 3.5-3
Weather Observation Service Standards
SERVICE LEVEL A
Service Level A consists of all the elements of
Service Levels B, C and D plus the elements
listed to the right, if observed.
10 minute longline RVR at precedented sites or
additional visibility increments of 1/8, 1/16 and 0
Sector visibility
Variable sky condition
Cloud layers above 12,000 feet and cloud types
Widespread dust, sand and other obscurations
Volcanic eruptions
SERVICE LEVEL B
Service Level B consists of all the elements of
Service Levels C and D plus the elements listed to
the right, if observed.
Longline RVR at precedented sites
(may be instantaneous readout)
Freezing drizzle versus freezing rain
Ice pellets
Snow depth & snow increasing rapidly remarks
Thunderstorm and lightning location remarks
Observed significant weather not at the station
remarks
SERVICE LEVEL C
Service Level C consists of all the elements of Service
Level D plus augmentation and backup by a human
observer or an air traffic control specialist on location
nearby. Backup consists of inserting the correct value if
the system malfunctions or is unrepresentative.
Augmentation consists of adding the elements listed to
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