Are web method calls synchronous (not counting result/fault handlers)?

Take the following code:

<?xml version="1.0" encoding="utf-8"?>

<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" creationComplete="ws.loadWSDL('someWSDL');">

    <mx:Script>

        <![CDATA[

            private function onLoad():void

            {

                ws.WebMethodCall("msg");

                navigateToURL(new URLRequest("someURL"), "_self");

            }

        ]]>

    </mx:Script>

    <mx:WebService id="ws" load="onLoad()">

        <mx:operation name="WebMethodCall"/>

    </mx:WebService>

</mx:Application>

Will ws.WebMethodCall("msg"); definitely fully transmit the method call to the server before the next line is entered into?  I know that the server may take time to process the call and try to resond, but that's not what I'm talking about.  Will the call definitely be transmitted to the server, as in a ball being thrown from one person to another in a game of catch, before the next line of code is entered into and executed?  Is there any chance whatsoever that navigateToURL may provoke a fault?  Thank you.