Originally Posted by DAL4EVER

Not knowing specifics, but the only way an ADG can deploy on the ground sans a manual deployment is through a failure of the ground prox logic. Its been eight years or so but I recall that the ADG logic/ground prox was located on the DC Bat Bus. The backup was the parking brake. If the parking brake is turned off and the Bat is off then if the Ext. Power is turned off there is no more back up. In this scenario, if the Ground Prox loses power a microsecond before the ADG Auto Deploy logic then the ADG will sense it is losing AC Power and auto deploy the ADG.