Radio - CTAF, UNICOM and MULTICOM

Communications Frequencies - CTAF, UNICOM and MULTICOM

References

• AIM section 4−1−9 Traffic Advisory Practices at Airports Without Operating Control Towers
• AIM Section 2. Radio Communications Phraseology and Techniques, section 4−2−3. Contact Procedures
• FAA Advisory Circular AC 90-66B Non-Towered Airport Flight Operations
• FAA Pilot/Controller Glossary
• FAA Chart Supplements (current PDFs for all areas)

Overview

The terms UNICOM, MULTICOM, CTAF, FSS, etc are often confusing to the new pilot (and to the experienced pilot as well). Let's examine each term, and how each relates to the pilot at a practical level.

CTAF - COMMON TRAFFIC ADVISORY FREQUENCY

From the Pilot/Controller Glossary:

COMMON TRAFFIC ADVISORY FREQUENCY (CTAF) − A frequency designed for the purpose of carrying out airport advisory practices while operating to or from an airport without an operating control tower. The CTAF may be a UNICOM, MULTICOM, FSS, or tower frequency and is identified in appropriate aeronautical publications.

Basically, every airport either has an active tower overseeing aircraft traffic (on one or more specified frequencies), or pilot's self-announce their position and intentions on the published CTAF (possibly in coordination with a ground-based non-government UNICOM or FSS entity— see below). You should refer to FAA Advisory Circular AC 90-66B Non-Towered Airport Flight Operations for further details on how to properly self-announce.

The CTAF for an airport is shown on VFR charts in the airport data block followed by a 'C' inside of a solid colored circle. The CTAF is also listed in the airport entry in the chart supplement.

There are 8 UNICOM frequencies, most of which are also typically assigned as the CTAF at non-towered airports:

• 122.700 MHz
• 122.725 MHz
• 122.800 MHz
• 122.950 MHz (for use at towered airports only - never used as CTAF)
• 122.975 MHz
• 123.000 MHz
• 123.050 MHz
• 123.075 MHz

For non-towered airports, a UNICOM frequency is typically assigned if there is a ground-based entity to provide pilots with local weather, runways in use, FBO services, or other relevant airport information. This UNICOM frequency is also used as the CTAF (Common Traffic Advisory Frequency) and is listed in the chart supplement as "CTAF/UNICOM". This ground-based entity is usually the local FBO or airport admin office, although it can also be an automated system (see Automated UNICOM, below).

For towered airports, the UNICOM frequency 122.950 is assigned. Note that 122.950 is reserved for this use at towered airports and is not assigned for CTAF or UNICOM use at non-towered airports.

For all airports, towered or non-towered, even if an FBO handles UNICOM communications for the airport it may have its own frequency for more FBO-specific communications. These FBO-specific frequencies typically come from a group of frequencies called ARINC or ASRI. Unfortunately, neither the charts nor the chart supplement lists any ARINC or ASRI frequencies used by FBOs. To determine these for a given airport you typically need to refer to additional information sources such as ForeFlight, FltPlan.com, Pilots Guide, or the FBO's website.

AUNICOM - Automated UNICOM

From the chart supplement legend:

AUNICOM — Automated UNICOM is a computerized, command response system that provides automated weather, radio check capability and airport advisory information selected from an automated menu by microphone clicks.

As mentioned above, finding people to man UNICOM stations seems to be an ongoing and growing problem. Also, a separate automated weather reporting system (typically AWOS or ASOS) require a second frequency (and associated equipment). As a result, some airports have gone to a pilot activated AUNICOM (Automated UNICOM) system that operates on the UNICOM frequency.

Automated UNICOM is not currently explicitly shown on charts, but it is listed in the chart supplement as AUNICOM rather than UNICOM in the communications section of the airport entry. For example, here is an excerpt from the chart supplement for Apple Valley KAPV:

Note the line that says:

COMMUNICATIONS: CTAF/AUNICOM 122.8

Although the pilot activation details can vary from system to system, automated UNICOM or weather is usually activated with multiple mic clicks, similar to activating pilot controlled lighting. In many cases 3 clicks will active the advisory broadcast and 4 clicks will activate a radio check "echo back." Some chart supplement entries include a comment about how to activate the system. Note the line that says:

COM/NAV/WEATHER REMARKS: Automated UNICOM–3 clicks advisory, 4 clicks radio check.

A warning when using AUNICOM: Activating AUNICOM when the frequency is already busy with pilot-to-pilot communications can be distracting at best, and dangerous at worse (if it causes more critical radio calls to obscured). Activating AUNICOM should typically be reserved for when there is little to no radio traffic already on frequency.

MULTICOM

From the Pilot/Controller Glossary:

MULTICOM − A mobile service not open to public correspondence used to provide communications essential to conduct the activities being performed by or directed from private aircraft.

There is a single MULTICOM frequency:

• 122.900 MHz

MULTICOM (122.9) is used as the CTAF (Common Traffic Advisory Frequency) at airports with no tower, FSS, or UNICOM.

Summary

Some key takeaways from the above information:

• Airports assigned a CTAF of 122.9 (aka MULTICOM) have no UNICOM and typically very few if any services.
• At airports with part-time towers, the tower frequency is almost always used as the CTAF when the tower is closed.
• Airports with a UNICOM frequency as the CTAF may or may not respond to a call to UNICOM requesting advisories, but may respond more readily to requests for fuel or parking after you have landed.
• At towered airports, 122.95 is the assigned UNICOM frequency.
• At larger airports, or airports with multiple FBOs, FBO operations tend to use non-UNICOM frequencies from the ARINC or ASRI allocations.