Paul kgyy wrote:

They want to know that you hear them. Sometimes I've just replied
"roger, 27D" but it's not much more of a deal to say "2994, 27D" which
I guess is what I will do from now on.


And you can drop the 2 to be even shorter. I generally just give the
last three digits as the first is obvious from the last three ... at
least at any altitude I'll ever fly at! :-)


Matt