EnityClientPlayerMCP.java
----------------------------

if(vars.fly) //if it's on
            {
                vars.Chat("Flying Enabled");//read further, this is an awesome shortcut
        	}
        	if(!vars.fly) //! means fly is off
            {
                vars.Chat("Fly Disabled");//read further, this is an awesome shortcut

GUIINGAME.JAVA
-------------------------
if(vars.fly) //if it's on
        {
    		mc.thePlayer.capabilities.isFlying = true;
    	}
    	if(!vars.fly) //! means fly is off
        {
    		mc.thePlayer.capabilities.isFlying = false;