The decision height varies according to the type of approach being flown ie Precision / Non Precision,the airfield in use, the category of aircraft being flown and sometimes the experience of the pilot. The decision to land or not can be made at any time it isn't just made at the decision height. The decision height is the point at which if your not visual and within the landing criteria you have to go around.
Your not totaly commited to a landing until the speedbrakes pop up on touchdown ie you can still go around below decision. Should the aircraft become unstable at any stage a go around should be initiated thats above and below decision.
The go around is normaly initiated by the pilot pressing the TOGA switches and rotating the aircraft into the climb. The go around is normaly flown by the pilot but on occasion it can be flown by the aircraft depending on the autopilot set up but even in this case the aircraft doesnt make the decision its the pilots.
We have to do a little work you know..
