ATIS vs CTAF explained: what each aviation frequency does, when to use it, how AWOS and UNICOM differ, and how to make correct simulator calls.
ATIS is a one-way broadcast of recorded airport, weather and operational information, usually identified by a letter code. CTAF is a shared advisory frequency used chiefly at non-towered airports, or when a tower is closed, for position and intention reports. Listen to ATIS for information; use CTAF to coordinate traffic.
In Aviation & Real-World Flying and in flight simulators, the practical distinction is simple: ATIS tells you the airport's conditions and operating plan, while CTAF carries live traffic coordination. Our separate guide explains what an ATIS frequency broadcasts and how its information code is used.
ATIS vs CTAF at a glance
| Feature | ATIS | CTAF |
|---|---|---|
| Full name | Automatic Terminal Information Service | Common Traffic Advisory Frequency |
| Main purpose | Provides weather, runway and selected operational information | Allows traffic position and intention reports |
| Type of communication | One-way repetitive voice or digital information service | Shared two-way voice frequency |
| Typical use | Busier towered airports | Non-towered airports and towered airports after closure |
| What you hear | Wind, visibility, cloud, altimeter setting, approaches, runways and selected notices | Taxi, departure, arrival and traffic-circuit position reports; sometimes an airport advisory |
| Identifier | A phonetic code such as Alpha or Bravo | No information letter |
| Reply required | Do not transmit on the ATIS frequency; tell ATC which code you received | No reply to every call is expected, although pilots may coordinate when useful |
| Provides a clearance | No | No |
ATIS normally repeats continuously and receives a new phonetic identifier when the message is revised. CTAF has no repeating message because it is a designated communication channel, not an information broadcast.
Is ATIS an ATC frequency?
ATIS is an ATC information service, but it is not a two-way control frequency. Pilots listen without transmitting, copy the information letter and report it on their first call to the relevant controller, for example with Information Bravo.
The code tells ATC that the pilot has received that edition of the broadcast. A controller can still provide changes or corrections, and ATIS does not replace a complete briefing or every applicable notice.
What does CTAF stand for in aviation?
CTAF means Common Traffic Advisory Frequency. It is the frequency designated for airport advisory communications when an operating control tower is not providing the service.
Most transmissions are pilots announcing where they are and what they intend to do. Depending on the airport, a UNICOM operator or flight service facility may also provide an advisory, but nobody using CTAF automatically becomes a controller or assumes responsibility for separating aircraft.
CTAF terminology is prominent in FAA procedures and is used in some other jurisdictions, but frequency labels and reporting rules vary by country. Use the published local procedure rather than assuming that US phraseology applies everywhere.
Can an airport use both ATIS and CTAF?
An airport can publish both ATIS and CTAF, although they are normally used under different operating conditions rather than as interchangeable frequencies.
- Tower open: Listen to ATIS, then contact clearance delivery, ground or tower as appropriate. Communicate with ATC instead of making ordinary CTAF position calls.
- No operating tower: Obtain weather from the published service, monitor CTAF and make concise traffic reports. Do not expect a controller to answer.
- Tower closed: Check the published after-hours procedure. The tower frequency often becomes CTAF, but that is not universal, and the ATIS broadcast may stop or be replaced by automated weather.
A mistake we see constantly is assuming that the numerical tower frequency must always be CTAF after hours. Airport status and published data decide which frequency to use. Our arrival guidance explains when a VFR pilot should contact ATC and when to change to the destination CTAF.
ATIS vs AWOS vs CTAF: which service should you use?
Use ATIS or an automated weather service to gather conditions, then use the appropriate ATC or CTAF frequency for communication.
- ATIS: Provides weather plus operational details selected for arriving and departing traffic, often including runway and approach information.
- AWOS or ASOS: Primarily provides an automated weather observation. These services are common at non-towered airports and do not replace CTAF traffic calls.
- CTAF: Carries traffic advisories, position reports and intentions. It is not the airport's weather broadcast, even though pilots or a ground station may mention conditions.
At a typical non-towered airport, a pilot listens to AWOS or ASOS first and then changes to CTAF. The services may use separate frequencies, so check the airport data rather than guessing; our comparison of ATIS, AWOS and ASOS explains what information each weather service supplies.
Is CTAF the same as UNICOM?
CTAF and UNICOM are related but are not synonyms. CTAF is the designated advisory frequency; UNICOM is a non-government ground communication service, and its frequency is often designated as the airport's CTAF.
A UNICOM station may provide airport information, but it may also be unattended. Pilots still use the published CTAF for self-announced reports. See our explanation of how UNICOM communication differs from one-way ATIS information for the service-level distinction.
If search results brought you here for ATIS vs CloudCompare 2026, those terms are unrelated. CloudCompare is point-cloud processing software, not an aviation frequency or ATC service; the relevant aviation comparison is ATIS vs CTAF.
How do you use ATIS and CTAF in a flight simulator?
The correct simulator workflow is to gather airport information first, confirm whether the tower is operating and then select the communication frequency appropriate to that status.
- Check the airport data. Find the published ATIS, automated weather, tower and CTAF entries. Never assume every non-towered airport uses the same common frequency.
- Listen before transmitting. Copy the wind, runway, altimeter setting and ATIS letter, or obtain the available automated weather observation.
- Confirm the airport's status. Use ATC frequencies when the simulated tower is active. Use CTAF when the airport is non-towered or its tower is closed and CTAF is published.
- Select and monitor the correct COM radio. Check the active rather than standby frequency, audio-panel selection, radio volume and push-to-talk assignment.
- Make concise traffic calls. Give the airport name, aircraft identification, position and intention. Keep listening and looking for traffic after transmitting.
Simulator implementations differ. A built-in ATC system may play ATIS yet support CTAF only through menu-driven calls, or it may produce no response because no simulated station is listening. When flying with human controllers, use the controller or advisory frequency required by that network and the airport's operating status.
Where do you find the ATIS or CTAF frequency?
ATIS and CTAF frequencies are listed in the airport's communication data, charts or simulator airport information. Larger airports may have separate arrival and departure ATIS services, while a closed tower may use its former tower frequency as CTAF only during specified hours.
Simulator scenery, navigation data and radio logic do not always represent the same data cycle. If a frequency behaves unexpectedly, compare the simulator's airport information with the data being used for the flight and confirm that the tower is not open. For real-world flying, use current official aeronautical information rather than relying on a simulator database.
What should you say on CTAF?
A useful CTAF transmission identifies the airport, aircraft, position and intention without occupying the frequency longer than necessary.
Springfield traffic, Cessna One Two Three Alpha Bravo, ten miles west, inbound runway two-seven, Springfield traffic.Springfield traffic, Cessna One Two Three Alpha Bravo, left downwind runway two-seven, Springfield traffic.Springfield traffic, Cessna One Two Three Alpha Bravo, clear of runway two-seven, Springfield traffic.
Typical calls cover taxi, departure, inbound position, entry to the traffic circuit or pattern, downwind, base, final and clearing the runway. The recommended calls and circuit terminology depend on local procedure.
Avoid the vague transmission Any traffic in the area, please advise. It gives no position or intention and can cause several pilots to answer at once. Make your own useful report instead. A CTAF call is not a clearance, does not reserve the runway and does not guarantee that every aircraft has a working radio.
Why can you hear ATIS but nobody answers on CTAF?
Hearing ATIS confirms only that you can receive its broadcast; silence on CTAF does not necessarily indicate a fault.
- There may be no nearby traffic, or no pilot may have a useful reason to reply.
- The tower may be open, with traffic using tower rather than CTAF.
- The simulator may not model interactive CTAF transmissions.
- The active COM frequency, audio-panel source, microphone selector or push-to-talk control may be wrong.
- The simulator's airport data may contain a different or outdated frequency.
- Other traffic may be outside radio range, blocked by terrain or using a different multiplayer or online communication system.
CTAF calls are normally reports, not requests for acknowledgement. Even when nobody responds, continue making appropriate transmissions, monitor the frequency and maintain a visual scan; radio contact does not provide traffic separation.