How Does the Ram Air Turbine (RAT) Deploy and Generate Emergency Power?
Modern aircraft are designed with multiple backup systems, but in extremely rare emergencies where both engines or primary power systems fail, aircraft rely on one remarkable device:
The Ram Air Turbine (RAT).
What Is a Ram Air Turbine (RAT)?
A Ram Air Turbine is a small deployable turbine installed inside the aircraft fuselage or wing. In emergencies, it extends into the airflow and uses the aircraft’s forward speed to generate:
- Emergency electrical power
- Hydraulic power
The RAT operates like a small wind turbine driven by the aircraft’s motion through air.
Why Aircraft Need a RAT
Aircraft engines normally provide electrical and hydraulic power through:
- Engine-driven generators
- Hydraulic pumps
- Auxiliary Power Unit (APU)
If all of these systems fail simultaneously, the aircraft may lose:
- Flight controls
- Cockpit displays
- Navigation systems
- Communication systems
How Does the RAT Deploy?
Under normal conditions, the RAT remains stowed inside a compartment.
Deployment can occur:
- Automatically after total power loss
- Manually by pilot command
Once activated:
- Compartment doors open
- The RAT swings into the airflow
- High-speed air rotates turbine blades
Many systems use spring-loaded or hydraulic deployment mechanisms for rapid extension.
The Physics Behind RAT Operation
The RAT converts the aircraft’s kinetic energy into rotational energy.
Where:
- P = Available wind power
- ρ = Air density
- A = Turbine swept area
- V = Aircraft airspeed
How Does the RAT Generate Emergency Power?
As airflow spins the turbine blades, the RAT drives:
- Electrical generators
- Hydraulic pumps
Depending on aircraft design:
- Some RATs provide only hydraulic power
- Others provide electrical power directly
- Some systems provide both
The generated power is routed only to essential systems.
What Systems Does the RAT Power?
- Fly-by-wire flight controls
- Essential avionics
- Communication radios
- Navigation displays
- Hydraulic flight control systems
Why RAT Power Is Limited
The RAT is small compared to engine-driven generators.
Typical RAT output:
- 5–70 kW depending on aircraft type
Main engine generators can produce far more power than this.
How RAT Deployment Affects Aircraft Performance
When deployed, the RAT creates:
- Additional aerodynamic drag
- Reduced glide efficiency
- Slight aircraft vibration
Minimum Airspeed Requirement
The RAT depends entirely on airflow, meaning it requires minimum aircraft speed to function properly.
Below a certain airspeed:
- Turbine RPM drops
- Power generation decreases
Some RAT systems require approximately 140 knots or higher for effective operation.
Why RATs Are Often Installed Off-Center
Many aircraft place the RAT slightly off the fuselage centerline.
Reasons include:
- Cleaner airflow
- Better structural mounting points
- Avoidance of landing gear airflow disturbances
Real Aircraft That Use RAT Systems
- Airbus A320 family
- Boeing 777
- Boeing 787
- Airbus A350
- Military fighter aircraft
Famous Emergencies Involving RAT Deployment
RAT systems have helped save aircraft during:
- Dual engine failures
- Severe electrical failures
- Hydraulic emergencies
The RAT became especially famous after incidents like:
- Air Canada Flight 143 (“Gimli Glider”)
Future of Emergency Power Systems
- More efficient compact turbines
- Advanced battery systems
- Hybrid emergency power systems
- Electric aircraft backup architectures
Conclusion
The Ram Air Turbine (RAT) is one of aviation’s most important emergency systems. Using only airflow and aircraft speed, it can provide critical electrical and hydraulic power during catastrophic failures.
Although rarely used, the RAT has saved lives by allowing pilots to maintain control and safely land aircraft even after complete loss of normal power systems.
