10
$\begingroup$

In the United States, many non-towered airports have CTAF frequencies (often shared with UNICOM as well) that tend to overlap with various other airports within a 50-100 nm radius, at least in more populated areas and states. I personally do not find this practical, as it congests the frequency. Also, for every radio call, you have to carefully listen to each call in order to know with respect to which airport the aircraft is calling.

Of course, there are other hints such as runway numbers, but the congestion is still not ideal because it increases the workload, makes it harder for you to say something, and increases the probability of radio collisions. I also noticed that in my area (Northeast USA), the CTAF frequencies are typically multiples of 100 kHz, even though we have a 25 kHz channel spacing system in place.

My question is essentially, why is there such a huge degree of overlap? Are there really no unused frequencies remaining to assign to all these airports? And if the answer is no, how about transitioning to 8.33 kHz channel spacing? Does there exist any plan to have better separation of frequencies at any point in the future? I am not yet an experienced pilot, but I do think that the ability to listen to only your airport and not 2 to 4 additional ones could significantly reduce the workload associated with non-towered airport operations and radio communications.

Improve this question
$\endgroup$

1 Answer 1

Reset to default
8
$\begingroup$

The CTAF frequencies 122.7, 122.8 and 122.9 are called MULTICOM because they are deliberately not specific to one airport. These frequencies are holdovers from the days of 100kHz radios, when we didn’t have frequencies to spare. They’re also easy to remember and recognize.

Today, MULTICOM is still used for low-traffic airports, so there shouldn’t be too much congestion, and the same frequency is often assigned to clusters of airports in close proximity so that you’re aware of other traffic in the general area—or in practice areas between those airports.

With the advent of 25kHz radios, it became possible to move every airport with UNICOM service to a discrete frequency, and for the most part, this has been done. If your airport hasn’t changed, you can discuss that with the airport manager and/or FBO, and they can contact the FAA to get a discrete frequency if warranted. Note they may have deliberately not done that for safety reasons due to proximity with MULTICOM airports.

Also, UNICOM frequencies still do get reused, just like any other “discrete” frequency. Reuse distance is based on the expected altitude of aircraft using it, so you will occasionally hear aircraft far away if one or both of you is higher than expected. For instance, you may hear distant traffic at 3k AGL that goes quiet as you descend and enter the pattern at 1k AGL. That is normal.

Improve this answer
$\endgroup$
4
  • 1
    $\begingroup$ For clarification, in NJ, even at pattern altitude, I can typically hear multiple other airports. The majority of airports indeed use 122.7, 122.8, 122.9, or 123.0. $\endgroup$
    – aviator
    Jun 26, 2021 at 16:41
  • 1
    $\begingroup$ @aviator On a UNICOM or MULTICOM frequency? $\endgroup$
    – StephenS
    Jun 26, 2021 at 16:44
  • 1
    $\begingroup$ CTAF/UNICOM, there is rarely a MULTICOM (at least judging from the chart supplements) $\endgroup$
    – aviator
    Jun 26, 2021 at 16:51
  • $\begingroup$ "MULTICOM because they are deliberately not specific to one airport", yes, the specificity of multicom is this is a service which frequency is reserved but not licensed to any ground station in particular (air-air links). Unicom is a ground station for ground-air links, with a licensed frequency. $\endgroup$
    – mins
    Jul 6, 2021 at 18:52

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .