When does the RAT automatically extend?

The correct answer is that the RAT (Ram Air Turbine) automatically extends with a speed above 100 knots and the loss of AC buses 1 and 2. This situation is critical because the RAT is designed to provide emergency power to essential systems in the event of total electrical failure.

When the aircraft experiences significant power loss, specifically the failure of both primary AC buses, the system recognizes that an emergency power source is needed to maintain flight control and essential systems. The operation of the RAT is dependent on sufficient airspeed, as it uses the airflow over the aircraft to generate power. Therefore, if the aircraft is traveling faster than 100 knots, the airflow is sufficient for the RAT to produce the necessary hydraulic and electrical power to support critical systems, helping to ensure the safety and control of the aircraft during such emergencies.

In comparison, the other choices do not align with the specific conditions that trigger the automatic extension of the RAT. For instance, switching off the batteries above 100 knots or having the APU generator as the sole power source doesn't create the emergency condition that necessitates RAT deployment. Similarly, a dual IRS failure does not automatically lead to a situation where the RAT must deploy, as it is not related to the electrical power management