What are you speaking about ?
What is waiting ? For what ?
Flex is asynchron, you don't wait, you react to events.
Flex is asynchronous, so you can't have any part of your app depend on the data being back. Rather, you do things once the data is back. So in your result handler after data has been processed you might call a function or set a bindable variable, indicating the app is in a state for the next operation to continue.
If you really wanted to force this issue, you could use a Timer (see FB3 help sys), but that is an undesireable hack.