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AIM

10/12/17

7

−1−31

Meteorology

e.

TBL 7

−1−3 contains a comparison of weather

observing programs and the elements reported.

f. 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 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 7

−1−4.

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.

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. 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.

3. 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 special
airports in other ways that have worse than average
bad weather operations for thunderstorms and/or
freezing/frozen precipitation, and/or that are remote
airports.

4. 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 7

−1−3

Weather Observing Programs

Element

Reported

W

ind

V

isibility

T

emperatur

e

Dew Point

Altimeter

Density 

Altimeter

Cloud/Ceiling

Pr

ecipitation

Identification

Thunderstorm

/

Lightning

Pr

ecipitation

Occurr

ence

Rainfall

Accumulation

Runway Surface

Condition

Fr

eezing Rain

Occurr

ence

Remarks

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 JO 7900.5B, Surface Weather Observing, for element reporting.