CTAF, UNICOM, and MF
Airports without a control tower (or other air-traffic facility) normally publish a standard frequency for pilots to communicate with each-other: in the US, for example, this is called the Common Traffic Advisory Frequency (CTAF), and in Canada, it is called Aerodrome Traffic Frequency (ATF). When making calls on the CTAF, the pilot addresses them to "Traffic" (e.g. "Ogdensburg Traffic, Grob 123 downwind for runway 09").
These airports may also have a facility that is (sometimes) staffed by someone who is not an air-traffic controller or flight-services specialist, for example, a dispatcher at a flight school, or a fuel operator at an FBO. These people cannnot give official clearances, but they can often provide a field advisory including the current temperature, altimeter setting, wind, runway surface condition, fuel availability, and any known traffic, and can also provide radio checks and similar services. The frequency for obtaining the advisory is called the UNICOM (Universal Communications).
Most of the time, the CTAF and UNICOM frequencies are the same, but they can occasionally be different. The pilot should address only specific requests to "UNICOM" (e.g. "Brockville UNICOM, this is Cessna ABC, radio check seat one."). All position reporting should be addressed to "Traffic" over the CTAF; otherwise, the poor UNICOM operator will keep running to the mic thinking that someone is making a request.
Note that many airports have control towers that are not open 24/7. When the control tower is closed, the tower frequency will typically become a CTAF, and pilots do their own position reporting, as at any uncontrolled field.
In Canada and some other countries, when talking over the CTAF/ATS is required, it is referred to as the MF (Mandatory Frequency), and will often be monitored by a flight-services specialist. The MF is typically for limited hours, and outside of those, it also becomes a CTAF. If there is an FSS specialist monitoring the MF, then the pilot will address calls to "Radio" (e.g. "Kingston Radio, Cherokee FBJO turning left base 19."); otherwise, the pilot will address them to "Traffic", as with the CTAF.
Even without an MF, it is generally recommended that pilots of aircraft having radio equipment permitting two-way communications should contact the Airport UNICOM to obtain advisory information, and announce their intentions over the CTAF when within ten (10) miles of the Airport. Pilots are also encouraged to maintain a listening watch on the frequency when operating within a ten mile radius of the Airport. All departing aircraft shall announce on the CTAF their intention and runway to be used for departure.
On initial contact, pilots report altitude, aircraft type and identification, and location relative to the airport and state their intention, to land or overfly.
Pilots give position reports on downwind and final approach, and will often make an optional call on the base leg as well.
FlightGear does not fully implement CTAF entirely. CTAF works best in multiplayer, where you actually have listeners (though in real life, pilots often broadcast blind over a CTAF with no listeners, too).
- To access CTAF or UNICOM, press the dash key (-) to enter the radio chat menu. Press the number that corresponds to '[XXX TRAFFIC]'
(where 'XXX' corresponds to the airport you are closest), then choose your message.
Air Traffic Control
See Air Traffic Control for the main article about this subject.
- ATC chatter (enable "Chatter" from the File > Sound Configuration dialog): plays random records of real ATC communications, probably best left disabled if going for multi-player mode with voice communications
- ATIS generated from current METAR (tick the somewhat misleadingly named "ATC" sound configuration option): set COM1 to the ATIS frequency of the closest airport to hear a faint broadcast automatically generated by FlightGear—in a controlled multiplayer session and with FGCom turned on, you may hear a proper ATIS if it was recorded by the ATC, so always tune in first!
- FGCom (enable it from the multiplayer menu): for voice communications over the multiplayer network.
- Spoken_ATC (available as addon): allows to listen to the directives of the Air Traffic Controller.
The Automatic Terminal Information Service is broadcast from most airports, informing about active runways, weather and conditions, exceptional airport information, etc. It is typically recorded every half-hour by controllers and looped over on a published frequency for pilots to listen before making contact.
Most radio racks have similar controls. As an example look at the Kx165 VHF communication transceiver and VHF navigation receiver.