Ram Air Turbine ( RAT)
How the Ram Air Turbine (RAT) Protects Modern Aircraft During Emergencies
Description
Discover how the Ram Air Turbine (RAT) works, why it is essential to aviation safety, and how modern airliners use this emergency power system.
Ram Air Turbine (RAT): The Emergency
Lifeline of Modern Aircraft
1.0 Introduction
What happens if a modern airliner suddenly loses all engine power and most of its electrical generation capability?
To many people, this scenario sounds catastrophic. Yet commercial aircraft are designed with multiple layers of redundancy, and one remarkable device quietly stands ready to preserve critical flight systems when conventional power sources fail—the Ram Air Turbine (RAT).
Although rarely seen during normal operations, the RAT represents one of aviation engineering’s most elegant emergency solutions. By harnessing airflow created by the aircraft’s motion, this small deployable turbine can generate hydraulic pressure, electrical power, or both, allowing pilots to retain essential flight controls and avionics.
The system gained worldwide attention after the successful ditching of US Airways Flight 1549 and Air Transat Flight 236, demonstrating how modern redundancy concepts protect aircraft and their occupants during extreme emergencies.
Understanding the Ram Air Turbine is valuable not only for pilots and engineers but also for aviation students and enthusiasts seeking insight into the sophisticated safety philosophy behind modern aircraft design.
2.0 Table of Contents
- Overview of the Ram Air Turbine
- Components and System Architecture
- How the Ram Air Turbine Works
- Functions, Applications, and Safety Benefits
- Advanced Technology and Lesser-Known Facts
- Key Takeaways
- Quick Facts Box
- Terminology Box
- Frequently Asked Questions
- Conclusion
- Discussion Questions
3.0 Overview of the Ram Air Turbine
What Is a Ram Air Turbine?
A Ram Air Turbine (RAT) is a deployable emergency power device designed to provide limited hydraulic and/or electrical power following the loss of normal aircraft power sources.
When deployed into the airstream, the turbine spins due to ram air generated by the aircraft’s forward movement.
The resulting mechanical energy drives:
- Hydraulic pumps
- Electrical generators
- Emergency power systems
4.0 Primary Purpose
The RAT exists to ensure continued operation of essential systems, including:
- Flight controls
- Critical avionics
- Primary flight instruments
- Navigation equipment
- Communication systems
- Hydraulic actuators
Its purpose is not to restore full aircraft capability but to provide enough power to maintain safe flight and landing.
5.0 Historical Background
Early jet transports depended primarily on hydraulic and engine-driven systems.
As aircraft evolved into highly computerized fly-by-wire designs, engineers introduced increasingly sophisticated emergency power architectures.
Important milestones include:
1960s–1970s
- Military aircraft adopted early RAT systems.
1980s
- Airbus introduced advanced fly-by-wire aircraft with integrated RAT capability.
1990s–Present
Modern airliners such as:
- Airbus A320 Family
- Airbus A330
- Airbus A350
- Boeing 777
- Boeing 787
incorporated highly reliable RAT systems as part of their redundancy philosophy.
6.0 Components and Architecture
Although designs vary between manufacturers, a typical Ram Air Turbine system consists of several major elements.
- Turbine Assembly
The deployable propeller-like rotor converts airflow into rotational energy.
Typical characteristics:
- Diameter: 20–63 inches
- High-speed rotation
- Lightweight composite construction
- Automatic deployment mechanisms
- Generator or Hydraulic Pump
Depending on aircraft design, the RAT may drive:
Hydraulic Pumps
Common on earlier Airbus aircraft.
Provides pressure for:
- Flight controls
- Slats and flaps (limited capability)
- Braking systems
- Electrical Generators
Common on Boeing 787 and Airbus A350.
Supplies emergency electrical power to:
- Flight control computers
- Essential avionics
- Navigation systems
- Deployment Mechanism
The RAT is normally stored inside the fuselage.
Deployment may occur:
Automatically
Triggered by:
- Dual engine failure
- Total AC power loss
- Hydraulic system failures
Manually
Pilots can command deployment using cockpit controls.
- Control Electronics
Modern aircraft monitor:
- Airspeed
- Electrical buses
- Hydraulic pressures
- Generator outputs
Flight control computers determine when deployment is necessary.
7.0 How the Ram Air Turbine Works
Step 1: Loss of Normal Power
Failures may include:
- Dual engine flameout
- Loss of generators
- Severe electrical faults
- Hydraulic failures
Step 2: Automatic Deployment
A door opens beneath the aircraft.
Spring or hydraulic actuators extend the turbine into the airflow.
Step 3: Airflow Spins the Turbine
As the aircraft moves forward, ram air rotates the blades.
No fuel is required.
No engine power is needed.
The aircraft’s speed becomes the energy source.
Step 4: Mechanical Energy Is Produced
The spinning turbine drives:
- A hydraulic pump
or - An emergency generator
depending on aircraft design.
Step 5: Essential Systems Receive Power
Power is directed to critical equipment:
Flight Control Computers
Maintaining controllability.
Primary Flight Displays
Providing attitude, airspeed, and altitude information.
Communication Radios
Allowing crews to coordinate with ATC.
Navigation Systems
Ensuring continued situational awareness.
8.0 Pilot Interaction
Modern aircraft automate much of the process.
Pilots primarily:
- Verify deployment.
- Monitor emergency electrical configuration.
- Follow QRH procedures.
- Manage aircraft energy and glide performance.
- Prepare for diversion or landing.
9.0 Functions and Applications
Maintaining Flight Control
Fly-by-wire aircraft depend heavily on computers.
Without electrical power, control laws could be severely degraded.
The RAT ensures continued operation of:
- Elevator actuators
- Ailerons
- Rudder systems
- Flight control computers
10. 0 Emergency Electrical Power
Aircraft such as the Boeing 787 use the RAT primarily as an electrical source.
Essential buses remain energized for:
- Displays
- FMC functions
- Navigation systems
- Radios
11.0 Hydraulic Backup
On Airbus aircraft, the RAT can supply hydraulic pressure to critical systems.
This capability supports:
- Pitch control
- Roll control
- Yaw control
12.0 Redundancy and Safety
The RAT is only one layer among several:
- Engine-driven generators
- APU generator
- Batteries
- Ram Air Turbine
This layered architecture reflects the aviation principle:
No single failure should result in loss of the airplane.
13.0 Real-World Examples
- Air Transat Flight 236 (2001)
After fuel exhaustion over the Atlantic, the Airbus A330’s RAT deployed automatically.
The crew successfully glided approximately 65 nautical miles to Lajes Air Base.
- US Airways Flight 1549 (2009)
Following a bird strike and dual engine failure, the Airbus A320’s RAT deployed.
The emergency systems helped maintain control during the famous Hudson River ditching.
- Airbus A330 and A350 Families
Automatic RAT deployment is part of normal emergency design philosophy.
14.0 Advanced Technology and Lesser-Known Facts
Integration with Fly-by-Wire Systems
Modern aircraft rely on:
- Flight control computers
- Electrical buses
- Hydraulic actuators
The RAT helps maintain these interconnected systems during severe emergencies.
15.0 Variable-Speed Operation
Modern RAT generators are designed to operate across wide airspeed ranges.
Higher speed generally means:
- Increased turbine RPM
- Greater power generation
16.0 Redundancy Philosophy
Airliners typically contain:
- Multiple generators
- Multiple hydraulic systems
- Backup batteries
- Auxiliary Power Units
- Ram Air Turbines
This approach follows FAA and EASA certification requirements emphasizing fault tolerance.
17.0 Engineering Insight
The RAT does not require:
- Fuel
- Combustion
- Engine rotation
It transforms the aircraft’s kinetic energy into emergency power.
In essence, the airplane becomes its own energy source.
18.0 Future Developments
Aircraft designers continue improving:
- Lightweight composite blades
- Higher-efficiency generators
- Smart power electronics
- Enhanced fault detection
Future More-Electric Aircraft architectures may further optimize emergency power systems.
19.0 Key Takeaways
- The Ram Air Turbine is an emergency backup power device.
- It deploys automatically after major power failures.
- Airflow provides the energy source.
- It can generate hydraulic pressure, electrical power, or both.
- Modern fly-by-wire aircraft rely heavily on RAT capability.
- The system preserves controllability and situational awareness.
- RAT deployment has contributed to several successful emergency outcomes.
- It forms part of a layered redundancy strategy.
- Pilots typically follow QRH procedures after deployment.
- The RAT enhances overall aviation safety.
20.0 Quick Facts Box
Item | Information |
System | Ram Air Turbine (RAT) |
Main Purpose | Emergency power generation |
Introduction | Military use in the 1960s; commercial expansion in the 1980s |
Typical Aircraft | A320, A330, A350, B777, B787 |
Power Source | Ram air from aircraft motion |
Major Components | Turbine, generator, hydraulic pump, controller |
Deployment | Automatic or manual |
Manufacturers | Collins Aerospace, Safran, Hamilton Sundstrand |
21.0 Frequently Asked Questions
- Does every airliner have a RAT?
No. Many large transport aircraft do, but designs vary depending on certification and system architecture.
- Can pilots manually deploy the RAT?
Yes. Most aircraft provide manual deployment capability.
- Does the RAT restart engines?
Not directly. It supplies emergency power needed to support restart attempts.
- Can the RAT provide full aircraft power?
No.
It only powers essential systems.
- Does the RAT work while the aircraft is stationary?
No.
Forward speed and airflow are required.
- Is RAT deployment common?
Very rare.
Most pilots never experience an actual deployment.
- Is the RAT visible from the cabin?
Usually not, though it may sometimes be seen depending on aircraft type and seating position.
- Can the RAT retract in flight?
Generally no. Once deployed, it remains extended until maintenance action after landing.
22.0 Conclusion
The Ram Air Turbine represents one of aviation engineering’s most elegant examples of redundancy and safety-focused design.
Although rarely used, it serves as a critical last line of defense when normal power sources are unavailable. By converting the aircraft’s motion through the air into usable energy, the RAT preserves flight control, communication, and navigation capabilities during some of the most challenging situations imaginable.
Real-world events have repeatedly demonstrated that this small device can play a major role in successful outcomes. As aircraft continue evolving toward more-electric architectures and increasingly sophisticated flight control systems, the importance of reliable emergency power generation remains unchanged.
In aviation, redundancy saves lives—and the Ram Air Turbine stands as a remarkable testament to that philosophy.
23.0 Discussion Questions
- Have you operated or studied the Ram Air Turbine system?
- Which aircraft family do you think employs the RAT most effectively?
- How should future more-electric aircraft improve emergency power capability?
- Share your experience or questions below.
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