UNICOM vs CTAF

[Aussie Andy]

I am a bit confused about the difference, when flying in the US, betweem UNICOM and CTAF. My questions are:

• What is the difference between UNICOM and CTAF?
• Does it matter?
• Why do some airports have both a TWR and UNICOM frequency?

My rough understanding is that both CTAF and UNICOM are used to make blind-calls, as we do here when TWR / RADIO etc. is unmanned, in order to get arifield / arrival information, which the Yanks (a term of enderment! ) seem to refer to as "traffic advisories", i.e. who is in the circuit, wind, which RWY is in use etc. I also understand that the frequencies allocated to these services are shared amongst a large number of non-TWR'd airfields, and thus you are likely to hear traffic and circuit calls from multiple airfields - hence use of the airfield name at the beginning and end of each transmission to avoid condusion. But I still don;t appreciate the difference between the two, hence my questions above.

Thanks PPruNers!


Andy

[englishal]

What is the difference between UNICOM and CTAF?

Essentially nothing. They are both used to announce your position / intentions. There may be some technical difference but in reality its the same (Unicom may be reserved for non airfield ops, like VFR corridors and the like).

Why do some airports have both a TWR and UNICOM frequency?

The UNICOM or CTAF frequency becomes active when the tower closes. Unlike the UK, you can still turn up at a large airport when it is closed, and it is treated like a "Radio" field in the UK. I landed at LGB 2am one morning, I had 5 runways, approach lighting system all at my disposal, and no one else there

Cheers

[Field In Sight]

Addressing the call to UNICOM is directing the call to (usually) the FBO on the field. i.e. for a taxi from the airport/fuel etc.

Otherwise direct your calls to TRAFFIC.

If it doesn't have a UNICOM/CTAF frequency then there is a general frequency 122.9 MULTICOM.



FIS.