When does the Air Driven Generator (ADG) deploy?

The Air Driven Generator (ADG) deploys when all AC power is lost. This mechanism is designed to provide an emergency source of electrical power to essential systems when the regular AC power sources, primarily the engines' generators, fail or become unavailable. When the aircraft experiences a complete loss of AC power, the ADG automatically activates and deploys, allowing it to harness airflow to generate electricity, which helps maintain critical operations and cockpit functionality until normal power is restored or the aircraft can land safely.

In contrast, the other scenarios do not accurately describe the operational triggers for the ADG. An engine failure may affect power output but does not specifically initiate the ADG deployment. Similarly, descending below a certain altitude or having it activate only during takeoff does not relate to its primary function of responding to total AC power loss.