Flash KeyboardEvent

Hi all. I am facing a problem with KeyboardEvent, I have written the following code

stage.addEventListener(KeyboardEvent.KEY_DOWN,on_keyDown);
private function on_keyDown(e:KeyboardEvent):void{
trace(“key down”);
}

It is working for some keys, but not for all, such as, it do nothing when I press delete key, ‘a’,‘s’ and many other keys.