Sean,

On Wed, 26 Mar 2008 20:34:44 -0400, Sean Breheny wrote:

> Hi all,
> 
> I live in the Boston area and I like to listen to VHF aircraft comms.
> I noticed something odd recently, though: it appears that Boston
> Approach is using duplex comms. I hear only the ground to air side of
> the communication on 124.4MHz and then an immediate reply from the
> aircraft on 133.0 MHz. I found this by chance because I had heard
> traffic on both of those frequencies while scanning around and finally
> started switching between them.

That is weird!

> I had thought that the VHF air band was simplex. A quick web search
> didn't yield any answers.

It *is* simplex, and for good reason - pilots need to hear what each other is saying, not just what ATC are saying - it's a safety thing.  Also, the airband isn't very 
wide, and it's quite crowded - there wouldn't be room to make it duplex.  Also, it would be very tricky to rely on pilots to select two frequencies for a single 
contact - it's just fraught with possible mistakes.
 
> Anyone know what is going on here?

No!  But they could be using two frequencies at once (one controller handling approach and tower, for example) - then you'd hear the controller on both 
frequencies, and the pilot on only one.

Cheers,


Howard Winter
St.Albans, England


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