Aeronautical Information Manual (AIM), page 473
5/26/16
12/10/15 AIM
e. TBL 7-1-3 contains a comparison of weather inserts the correct or missing value for the automated
observing programs and the elements reported. ASOS/AWSS elements. This service is provided by
air traffic controllers under the Limited Aviation
f. Service Standards. During 1995, a govern- Weather Reporting Station (LAWRS) process, FSS
ment/industry team worked to comprehensively and NWS observers, and, at selected sites,
reassess the requirements for surface observations at Non-Federal Observation Program observers.
the nation's airports. That work resulted in agreement
on a set of service standards, and the FAA and NWS Two categories of airports require detail beyond
ASOS sites to which the standards would apply. The Service Level C in order to enhance air traffic control
term "Service Standards" refers to the level of detail efficiency and increase system capacity. Services at
in weather observation. The service standards consist these airports are typically provided by contract
of four different levels of service (A, B, C, and D) as weather observers, NWS observers, and, at some
described below. Specific observational elements locations, FSS observers.
included in each service level are listed in 3. Service Level B is a service in which weather
TBL 7-1-4. observations consist of all elements provided under
1. Service Level D defines the minimum Service Level C, plus augmentation of additional data
acceptable level of service. It is a completely beyond the capability of the ASOS/AWSS. This
automated service in which the ASOS/AWSS category of airports includes smaller hubs or special
observation will constitute the entire observation, airports in other ways that have worse than average
i.e., no additional weather information is added by a bad weather operations for thunderstorms and/or
human observer. This service is referred to as a stand freezing/frozen precipitation, and/or that are remote
alone D site. airports.
4. Service Level A, the highest and most
2. Service Level C is a service in which the
demanding category, includes all the data reported in
human observer, usually an air traffic controller,
Service Standard B, plus additional requirements as
augments or adds information to the automated
specified. Service Level A covers major aviation
observation. Service Level C also includes backup of
hubs and/or high volume traffic airports with average
ASOS/AWSS elements in the event of an ASOS/
or worse weather.
AWSS malfunction or an unrepresentative
ASOS/AWSS report. In backup, the human observer
TBL 7-1-3
Weather Observing Programs
Runway Surface
Thunderstorm/
Accumulation
Freezing Rain
Cloud/Ceiling
Identification
Precipitation
Precipitation
Temperature
Occurrence
Occurrence
Condition
Lightning
Rainfall
Dew Point
Altimeter
Altimeter
Reported
Density
Remarks
Visibility
Element
Wind
Type
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
AWOS-4 X X X X X X X X X X X X
Manual X X X X X X X
REFERENCE- FAA Order 7900.5B, Surface Weather Observing, for element reporting.
Meteorology 7-1-29
Page 473 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures