AIM Text
- 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.
- At uncontrolled airports that are equipped with ASOS/AWOS with ground-to-air broadcast capability, 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. Some part-time towered airports may also broadcast the automated weather on their ATIS frequency during the hours that the tower is closed.
- 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.
Source: FAA Aeronautical Information Manual · current edition · paragraph 4-3-27.
The short answer
AIM 4-3-27 is FAA advisory guidance for operating at uncontrolled airports equipped with ASOS or AWOS. It explains that one-minute updated airport weather is available via ground-to-air broadcast within about 25 NM below 10,000 feet, and that pilots—who have more current weather than distant controllers—should monitor it, especially in Class E airspace where conditions affect IFR/VFR status.
Research Notes
Common Questions
How close to an ASOS/AWOS airport can I receive the one-minute weather?
Per AIM 4-3-27, at uncontrolled airports equipped with ASOS/AWOS that have ground-to-air broadcast capability, the one-minute updated airport weather should be available within approximately 25 NM of the airport below 10,000 feet. The broadcast frequency is published on sectional charts and in the Chart Supplement.
Why do controllers rely on the pilot for weather at these airports?
AIM 4-3-27 notes pilots have access to more current weather at uncontrolled ASOS/AWOS airports than controllers located several miles away. Controllers issue SVFR or IFR clearances based on pilot request, known traffic, and reported METAR/SPECI when available, and rely on the pilot to determine current airport weather from the ASOS/AWOS.
How should I request an approach after getting the one-minute weather?
Per AIM 4-3-27, if ATC service is required for IFR/SVFR or requested for VFR, advise the controller you have received the one-minute weather and state your intentions, for example: “I have the (airport) one-minute weather, request an ILS Runway 14 approach.” Pilots in Class E airspace must stay alert for changing conditions affecting IFR/VFR status.