AIM ¶ 4-3-27 — ASOS/AWOS Uncontrolled Airport Ops
AIM 4-3-27 explains pilot procedures at uncontrolled airports with ASOS/AWOS, including weather monitoring, frequencies, and ATC requests. Study guide for pilots.
In Plain English
At uncontrolled airports equipped with ASOS (Automated Surface Observing System) or AWOS (Automated Weather Observing System) with ground-to-air broadcast capability, you can receive one-minute updated weather within approximately 25 NM of the airport and below 10,000 feet. The broadcast frequency is published on sectional charts and in the Chart Supplement.
Why it matters operationally:
- Pilots at the airport have more current weather than ATC controllers who may be miles away.
- Controllers rely on you to determine current airport weather from ASOS/AWOS when issuing IFR or SVFR clearances.
- In Class E airspace, weather changes can shift the airspace status between IFR and VFR — monitor continuously.
- All arriving/departing aircraft should monitor the weather frequency to ascertain airspace status.
When requesting ATC service (IFR, SVFR, or VFR advisories), advise the controller you have the one-minute weather and state your intentions, e.g., "I have the (airport) one-minute weather, request an ILS Runway 14 approach." Some part-time towered airports also broadcast automated weather on the ATIS frequency when the tower is closed.
AIM Source Text
FAA AIM ¶ 4-3-274-3-27. 4-3-27. Operations at Uncontrolled Airports With Automated Surface Observing System (ASOS)/Automated Weather Observing System (AWOS)
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. EXAMPLE- “I have the (airport) one-minute weather, request an ILS Runway 14 approach.” REFERENCE- AIM, Para 7-1-10 , Weather Observing Programs. Previous | Top | Next AIM | ATPUBS | FAA | Send your comments regarding this website.
Oral Exam Questions a DPE Might Ask
Q1At an uncontrolled airport with ASOS/AWOS, within what range and altitude can you typically receive the ground-to-air weather broadcast?
Per AIM 4-3-27, the one-minute updated airport weather should be available within approximately 25 NM of the airport and below 10,000 feet.
Q2When requesting an IFR or SVFR clearance at an uncontrolled ASOS/AWOS airport, what should you tell the controller?
Per AIM 4-3-27, the pilot should advise the controller they have received the one-minute weather and state their intentions — for example, "I have the (airport) one-minute weather, request an ILS Runway 14 approach." Controllers rely on the pilot for current airport weather since they may be located miles away.
Q3Why is it important to monitor the ASOS/AWOS frequency when operating in Class E airspace at an uncontrolled airport?
Per AIM 4-3-27, pilots in Class E airspace must be alert for changing weather conditions that may affect the status of the airspace from IFR to VFR or vice versa, so monitoring the airport weather frequency helps ascertain the current status of the airspace.
Related Paragraphs in AIM Chapter 4