What is the purpose and operation of the Ram Air Turbine (RAT) on a narrowbody in an electrical outage?

• A. RAT provides emergency electrical power (and, in some designs, hydraulic power) during total loss of normal sources; it deploys automatically or manually per procedure.
• B. RAT powers the main engines.
• C. RAT cools the avionics.
• D. RAT is a decorative vent.

Answer: (C)

The key idea is that the Ram Air Turbine is an emergency power source used when all normal electrical (and sometimes hydraulic) sources are lost. It’s a small turbine that captures ram air from the airstream to spin up a generator and/or hydraulic pump. That means it can keep essential systems alive when the engines’ generators and the APU aren’t supplying power.

How it works in practice: during a total loss of power, the RAT deploys—either automatically, triggered by the aircraft’s systems, or manually by the crew per procedure. Once deployed, the turbine drives the emergency electrical generator to supply essential buses, and in some designs also drives a hydraulic pump to provide limited hydraulic pressure for critical flight-control surfaces and other essentials. It does not power the main engines, nor is it used for cooling avionics, and it certainly isn’t a decorative vent. The RAT’s role is to buy time by preserving the operation of vital systems until normal power can be restored.