What triggers the automatic deployment of the RAT?

The automatic deployment of the Ram Air Turbine (RAT) is primarily triggered by the loss of normal AC power. This event is critical because the RAT serves as an emergency power source when the aircraft's main electrical systems fail. The loss of normal AC power indicates that the aircraft is in a critical situation; hence, deploying the RAT provides essential electrical power and hydraulic pressure needed to maintain control and operation of the aircraft systems during emergency conditions.

In scenarios where normal AC power is lost, the RAT automatically extends into the airstream, generating its own power through the airflow. This is vital in ensuring that necessary systems can still function and that flight crew have control during an emergency.

Other potential triggers listed, such as excessive load on the electrical system or failure of the batteries, do not cause the RAT to deploy automatically. Instead, these situations may lead to different operational responses or require pilots to take action manually. Overheating of the generators may indicate issues, but it does not directly lead to the activation of the RAT. Thus, loss of normal AC power remains the key condition that triggers the RAT's automatic deployment for emergency power support.