flash action script press a keyboard letter

hello can anyone help all i want to do is press the "a" on the keyboa开发者_开发百科rd and it goes to frame 2 i have the following working button but this only works for up down left right etc

    this.onKeyDown = function() {
if (Key.isDown(Key.SPACE)) {
desert._visible = false;
forest._visible = false;
tunnel._visible = true;
gotoAndPlay(2);
}}

how do i change the above so instead of SPACE i can press "a"

You can find all available keycodes right here. A great resource on this topic.