Both terms come up at airports without an operating control tower. One is a frequency, the other is a ground radio station, and the exam likes to mix them up.
CTAF, the Common Traffic Advisory Frequency, is the frequency designated for airport advisory practices at an airport without an operating control tower. UNICOM is a nongovernment air/ground radio station that may provide airport information where there is no tower or FSS. A CTAF may be a UNICOM, MULTICOM, FSS or tower frequency.
The AIM names three ways for pilots to communicate and get airport and traffic information at an airport with no operating tower: by communicating with an FSS, with a UNICOM operator, or by making a self-announce broadcast. UNICOM stations can provide weather information, wind direction, the recommended runway, or other necessary information on pilot request. FSS airport advisories are available only in Alaska.
If an airport has no tower, FSS or UNICOM, the AIM table says to self-announce on the MULTICOM frequency 122.9. When a tower or FSS is not in operation, the table says to self-announce on the CTAF. The CTAF frequency is identified in aeronautical publications such as the Chart Supplement U.S., and the Study Guide says it can also be found on a sectional chart by the airport.
What it means for a remote pilot: the Study Guide says a remote pilot in command is not required to communicate with manned aircraft near a non-towered airport, but remote pilots should be familiar with traffic patterns, radio procedures and radio phraseology. The AIM warns that other aircraft may not have communication capability or may not announce their presence, so stay alert. The airspace authorization rule is explained on our 14 CFR 107.41 page.
Sources: AIM 4-1-9, Traffic Advisory Practices at Airports Without Operating Control Towers · FAA-G-8082-22, ch. 7, Radio Communication Procedures · FAA-H-8083-25C, ch. 14, Nontowered Airport
AIM 4-1-9, Communicating on a Common Frequency
A CTAF is a frequency designated 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.
AIM 4-1-9, Information Provided by Aeronautical Advisory Stations (UNICOM)
UNICOM is a nongovernment air/ground radio communication station which may provide airport information at public use airports where there is no tower or FSS.
FAA-G-8082-22, ch. 7, Radio Communication Procedures
A MULTICOM frequency of 122.9 will be used at an airport that is non-towered and does not have a FSS or UNICOM.
FAA-G-8082-22, ch. 7, Radio Communication Procedures
Although a remote pilot-in-command is not required to communicate with manned aircraft when in the vicinity of a non-towered airport, safety in the National Airspace System requires that remote pilots are familiar with traffic patterns, radio procedures, and radio phraseology.
Sources: AIM 4-1-9, Communicating on a Common Frequency · AIM 4-1-9, Information Provided by Aeronautical Advisory Stations (UNICOM) · FAA-G-8082-22, ch. 7, Radio Communication Procedures · FAA-G-8082-22, ch. 7, Radio Communication Procedures
Similar to the FAA test, not the actual test questions. Each answer shows its FAA source.
Question 1 of 3
(Few airports around the country do not have a CTAF or UNICOM frequency. A MULTICOM frequency of 122.9 will be used at an airport that is non-towered and does not have a FSS or UNICOM.)
FAA source: FAA-H-8083-25C ch. 14, Recommended communication procedures (Figure 14-1)
Question 2 of 3
According to the chart, the CTAF frequency next to the circle “C” symbol is 118.7 MHz.
FAA source: FAA-CT-8080-2H Appendix 1, Legend 1 Sectional Aeronautical Chart (Airport Data)
Question 3 of 3
(As seen in this figure, the CTAF frequency (next to the circled C) is 123.0.)
FAA source: FAA-H-8083-25C ch. 14, Nontowered Airport
MULTICOM is the frequency, 122.9, used for self-announce broadcasts at an airport that has no tower, FSS or UNICOM.
Sources: AIM 4-1-9 · FAA-G-8082-22, ch. 7
The AIM table shows inbound calls 10 miles out, then entering downwind, base and final, and leaving the runway. This is a reason to expect radio traffic near the airport.
Source: AIM 4-1-9
It quizzes you on questions like these, explains why each answer is right with the FAA page behind it, and retests the ones you miss. Free to start: 300 credits every month.
More on this topic: Part 107 operations and decision-making.