When is just clicking PTT an acknowledgement?

And, if you are in a crowded area, your "double-click" would probably "step
on" someone else's communication. If an acknowledgement is not required, it
would seem the best practice would be not to acknowledge, especially in
congested airspace...

"Blanche" wrote in message
...
Unfortunately when there are numerous aircraft in the vicinity, how is
the controller going to know which aircraft double-clicked and which
clicked by accident?