I don't think polling a remote URL is the best way to check for internet connectivity (At least every 3 seconds). AIR has the ability to check the network itself like so:
air.NativeApplication.nativeApplication.addEventListener(air.Event.NETWORK_CHANGE, onNetworkChange);
function onNetworkChange(event)
{
//Check resource availability
}
The Event.NETWORK_CHANGE event does not indicate a change in all network activity, but only that a network connection has changed. AIR does not attempt to interpret the meaning of the network change.
http://help.adobe.com/en_US/AIR/1.5/devappshtml/WS5b3ccc516d4fbf351e63e3d118666ade46-7fcc.html
With that said, I would put your polling request inside the onNetworkChange
event that way it checks only when necessary.