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AIM 

6/17/21 

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24 

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26.  Operations at Uncontrolled 

Airports With Automated Surface 
Observing System (ASOS)/Automated 
Weather Observing System (AWOS) 

a. 

Many airports throughout the National 

Airspace System are equipped with either ASOS or 
AWOS. At most airports with an operating control 
tower or human observer, the weather will be 
available to you in an Aviation Routine Weather 
Report (METAR) hourly or special observation 
format on the Automatic Terminal Information 
Service (ATIS) or directly transmitted from the 
controller/observer. 

b. 

At uncontrolled airports that are equipped with 

ASOS/AWOS with ground

to

air broadcast capabil-

ity, the one

minute updated airport weather should be 

available to you within approximately 25 NM of the 
airport below 10,000 feet. The frequency for the 
weather broadcast will be published on sectional 
charts and in the Chart Supplement U.S. Some 
part

time towered airports may also broadcast the 

automated weather on their ATIS frequency during 
the hours that the tower is closed. 

c. 

Controllers issue SVFR or IFR clearances 

based on pilot request, known traffic and reported 
weather, i.e., METAR/Nonroutine (Special) Aviation 
Weather Report (SPECI) observations, when they are 
available. Pilots have access to more current weather 
at uncontrolled ASOS/AWOS airports than do the 
controllers who may be located several miles away. 
Controllers will rely on the pilot to determine the 
current airport weather from the ASOS/AWOS. All 
aircraft arriving or departing an ASOS/AWOS 
equipped uncontrolled airport should monitor the 
airport weather frequency to ascertain the status of 
the airspace. Pilots in Class E airspace must be alert 
for changing weather conditions which may affect the 
status of the airspace from IFR/VFR. If ATC service 
is required for IFR/SVFR approach/departure or 
requested for VFR service, the pilot should advise the 
controller that he/she has received the one

minute 

weather and state his/her intentions. 

EXAMPLE

 

“I have the (airport) one

minute weather, request an ILS 

Runway 14 approach.” 

REFERENCE

 

AIM, Para 7

1

10, Weather Observing Programs. 

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32 

Airport Operations