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- Components of a RAT System
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- Power Generation
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- Automatic Deployment
- Manual Deployment
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- Real-World Examples
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- Airbus Aircraft
- Boeing Aircraft
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- Importance of Regular Testing
- RAT Testing Procedures
- Common Issues and Maintenance
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- Aircraft Handling with RAT Deployed
- Pilot Actions During RAT Deployment
- Limitations and Precautions
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- Training for RAT Scenarios
- Awareness and Preparedness
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Aircraft rely on their engines not just to propel them through the sky, but also power everything on board.
That includes things like lights and air conditioning, but also critical parts such as flight control hydraulics and cockpit displays.
But when all engines fail midflight, how do these important systems stay powered up?
A small wind-driven backup system called the Ram Air Turbine (RAT) is a last-resort source of power for a crippled aircraft. This is what pilots need to know about it.
Key Takeaways
- A Ram Air Turbine (RAT) is a small wind-driven unit that deploys when primary power is lost.
- It can provide emergency hydraulic and/or electrical power.
- RATs power only essential systems – flight controls and core avionics.
- Deployed RATs increase drag and shorten glides. The limited output reduces available systems.
What Is a Ram Air Turbine (RAT)?

A RAT, or Ram Air Turbine, is just a small fan that normally sits stowed inside the airframe. When primary power is lost, it swings into the airstream and spins, converting airflow into usable power.
Depending on the aircraft, that rotation drives a hydraulic pump, an electrical generator, or both.
The output is limited, so you can’t fly the aircraft like nothing happened. The RAT supplies power only to essentials such as flight controls and core avionics. This lets the crew maneuver the aircraft, navigate, communicate, and land safely in an emergency.
Components of a RAT System
Let’s look at its key components and features to understand how a Ram Air Turbine works.
Turbine Blades and Hub: The heart of the RAT is the small turbine or propeller that spins in the airflow. It usually has two or four blades attached to a central hub. These blades are shaped to capture oncoming air and rotate quickly.
Some modern RAT designs even use variable-pitch blades or built-in governors. This means the blade angle can adjust automatically to maintain an optimal rotational speed.
Power Unit: The spinning blades connect to the power unit, which can be a hydraulic pump, an electric generator, or even both.
In the first case, the spinning turbine drives a small hydraulic pump that pressurizes one of the aircraft’s hydraulic systems.
In other aircraft, the RAT directly turns an electric alternator or generator, supplying electricity to an emergency bus-bar that powers critical instruments and electronics.
Dual-drive designs are more complex. They pressurize hydraulics and generate electricity simultaneously.
Deployment Mechanism and Housing: The RAT is stowed in a flush compartment when unused. It’s often found in the fuselage belly, wing root fairing, or another nook on the aircraft’s underside.
How does the RAT deploy from the housing?
Many RATs are spring-loaded. The moment it is triggered, a latch releases and a spring pushes the RAT turbine assembly out into the wind.
Some aircraft might swing the RAT out with a small hydraulic or pneumatic actuator. In all cases, the mechanism is designed to work even with no electrical power.
How Does a RAT Work?

Upon an emergency trigger, the RAT swings out from its compartment into the slipstream. When exposed to oncoming air, the airflow’s force starts spinning the turbine blades.
As the RAT blades spin, they drive the attached hydraulic pump or electric generator. The turbine’s mechanical rotation is converted into fluid pressure or electrical current.
The spinning pump pressurizes fluid in a dedicated hydraulic line for a hydraulic RAT, typically feeding an emergency or standby hydraulic circuit.
For an electrical RAT, the spinning rotor in the generator creates electricity.
Power Generation
The faster the aircraft moves through the air, the more wind energy is available to spin the RAT, and hence, the more power it can generate.
As the aircraft slows down, the RAT’s output diminishes. Most RATs have a minimum airspeed below which they can no longer sustain the required power. For airliners, this is often around 120–150 knots.
When and How Does the RAT Deploy?

Automatic Deployment
Modern aircraft are designed to pop out the RAT automatically under specific severe failure conditions. This ensures no time is wasted if the situation is dire.
What triggers automatic deployment?
The classic trigger is the loss of all main engine-driven power sources. Many designs trigger the RAT if the aircraft’s AC electrical system goes dark.
The logic often includes an airspeed check to prevent deployment on the ground or at very low speeds erroneously.
Once automatically deployed in flight, the RAT generally cannot be retracted until the aircraft is on the ground.
Even if you somehow got an engine or APU running again later, the RAT usually stays out free-wheeling and is only cranked back into its bay by maintenance on the ground.
Manual Deployment
If automatic logic fails or a checklist calls for it, pilots can deploy the RAT with a guarded cockpit control, labeled something like “RAT MAN ON.”
Some aircraft also allow manual deployment on command for testing or training purposes. This usually happens on the ground or in simulators rather than in the real air, since you can’t stow it once it’s out in flight.
Importance of the RAT in Emergency Situations

The most immediate benefit of a deployed RAT is restoring or maintaining hydraulic pressure for control surfaces. If hydraulic pressure is lost in a jet, controls become incredibly heavy or inoperative.
A hydraulic pump powered by the RAT pushes fluid into the lines so that ailerons, elevators, rudders, and spoilers can move again.
Along with control surface movement, an equally vital aspect is keeping essential electrical systems running. When you lose all generators, you don’t want to be flying blind.
If the RAT drives a generator or emergency alternator, it will power crucial instrument displays, including the attitude indicator, altimeter, airspeed, and navigation. Add to that possibly one communication radio and transponder.
Real-World Examples
US Airways Flight 1549 was an Airbus A320 taking off from LaGuardia Airport in 2009. Right after takeoff, it struck a flock of geese and lost thrust in both engines. With dual engine failure, the aircraft’s systems automatically deployed the RAT immediately.
This provided hydraulic power for the fly-by-wire controls and essential electrics. It allowed the captain to perform a controlled ditching on the Hudson, with all souls surviving.
The RAT doesn’t just help out for short intervals. In 2001, an Air Transat Airbus A330 was en route over the Atlantic when a massive fuel leak caused both engines to flame out while still about 65 nautical miles from the nearest airport.
The RAT’s hydraulic pump pressurized the flight controls, and an emergency generator provided basic electrics. This allowed the pilots to glide the aircraft with over 300 people on board for over 15 minutes, covering roughly 120 km with zero thrust.
Without the RAT, maintaining control of the aircraft for that distance and navigating to the remote island airfield would likely have been impossible.
RAT Systems in Different Aircraft Models

Airbus Aircraft
Airbus RATs are typically designed to provide both hydraulic and electrical power. They are integrated with one of the hydraulic systems and will drive an emergency generator.
Airbus pilots should know their specific RAT airspeed limitations and the location of the manual deploy switch. Airbus RATs may stall at low speeds, so keep that energy up until landing.
Also, once the RAT is out, certain systems, including autopilot and some flight control laws, will be disabled. That means the aircraft needs to be flown with a degraded configuration. It may have some safety protections disabled, but it will remain controllable.
Boeing Aircraft
Boeing also equips many of its jets with RATs, though their philosophy can differ slightly. Generally, older Boeing designs relied more on redundancies such as multiple engines, APU, and battery. Not all had RATs. Newer designs and those meant for ETOPS flights do have RATs.
Interestingly, Boeing’s counterpart of the A320, the 737, doesn’t have a RAT. It compensates using dual engine generators and a standby system with battery and an APU for backup.
On some older Boeing models, such as the 767, the RAT was more of a hydraulic backup because Boeings had historically used triple or quad hydraulic systems.
Newer Boeing jets like the 787 focus on electric power output because many of its systems are electrically actuated.
Testing and Maintenance of RATs

Importance of Regular Testing
Since RATs are rarely used, it’s crucial that they are regularly tested and maintained to ensure they’ll work perfectly when needed. Aviation regulators and manufacturers have procedures and intervals to check RAT functionality.
If a RAT is never swung out, you might not know that a hinge is corroded or a pump shaft is sticking. A test deployment might reveal odd noises, slower-than-expected spin-up, or an indicator light malfunction. Fixing those proactively prevents an in-flight failure of the RAT.
RAT Testing Procedures
How do you test a RAT on the ground without actually causing an in-flight emergency? There are special procedures and equipment for this.
Maintenance crews use RAT test rigs or hydraulic mules to test. These ground power units simulate the conditions needed for RAT operation.
One common method for a hydraulic RAT involves connecting a hydraulic test cart to the aircraft’s hydraulic system. This test simulates pressure loss or drives the RAT’s hydraulic motor.
Alternatively, some RATs can be deployed on the ground and then a wind stream or motor is applied to spin them. There are even specialized windmill test stands that rotate the RAT blades at the required RPM.
For electric RATs, a test might involve letting it power some dummy load or verifying it can power the actual essential bus.
Common Issues and Maintenance
- One potential problem is the RAT failing to deploy when commanded. This could be due to a jammed mechanism, such as a sticky hinge, a corroded pin, or a failed release latch.
Often, the fix might be lubricating moving parts, adjusting the spring tension, or replacing a faulty actuator. - Over time, the RAT’s efficiency might degrade. Worn turbine blades can make the RAT less effective at capturing air energy.
Similarly, a hydraulic pump with internal wear might not build pressure to spec. Or an electrical generator might have worn bearings or brushes, causing lower output. Maintenance addresses these by overhauling or replacing components at intervals. - A common maintenance task is checking the hydraulic lines and fittings associated with the RAT pump. After deployment tests, they’ll inspect for any signs of fluid leakage around the RAT pump or the connecting lines. Leaks would be fixed by replacing seals or lines.
- RAT deployment is triggered and detected by sensors. If a switch that senses RAT locked down is faulty, the cockpit might not get a “RAT deployed” indication even if it is out. Maintenance will check these switches and wiring.
Operational Considerations for Pilots

Aircraft Handling with RAT Deployed
Due to the deployed RAT, expect modestly higher drag and a shorter glide. You’ll have to manage the aircraft’s energy accordingly. Depending on control laws and available hydraulic pressure, handling may feel heavier or more “direct.”
Only essential systems are powered, so autopilot, anti-ice, passenger services, and some displays may be unavailable. You might slowly lose cabin pressurization, so you may have to descend to breathable altitudes.
The landing distance also increases since you won’t have reversers. It can increase further if anti-skid or spoilers aren’t fully available. That’s why you should favor longer runways and plan stopping margins accordingly.
Pilot Actions During RAT Deployment
The immediate action in a dual-engine failure or total power loss is to fly the aircraft. This means pitch for glide speed and establish positive control. Once that’s done, run the memory items or checklist.
The RAT should deploy automatically, but if the RAT didn’t auto-deploy, one pilot will likely have to deploy it manually. If, after doing so, they still don’t see the expected signs (meaning the RAT failed), then the situation is even more dire.
Limitations and Precautions
Respect the aircraft’s specified minimum RAT speed to avoid turbine stall and loss of pressure or power. That’s often on the order of 140 knots.
You’ll have to manage the aircraft’s flap and landing gear configuration to balance drag and control. That means using reduced flaps and possibly delayed gear extension to maintain the speed.
Due to the limited supply offered by the RAT, it’s best to conserve electrical load. Anticipate degraded braking or anti-skid, and brief that this is a single-attempt landing. Keep situational awareness high from glide planning through rollout.
If you let the speed fall below the threshold too early, the RAT could stop providing power seconds before touchdown, when you might need a last-moment flare input. That’s why it’s good to plan a slightly faster approach and be ready for a faster touchdown.
The Role of Pilot Knowledge and Training

Training for RAT Scenarios
Airlines and flight training programs include RAT deployment scenarios in their curriculum, especially for those flying multi-engine transport aircraft.
Modern full-flight simulators can accurately simulate dual-engine failures and RAT deployments. Pilots are put through these paces in recurrent training sessions. Doing this in a simulator builds muscle memory and reduces panic if it ever happens for real.
Awareness and Preparedness
Good pilots don’t wait for an emergency to crack open the manual. They regularly study their aircraft’s systems, including the rarely used ones. By engaging with these materials, pilots keep the knowledge fresh.
Being realistic about what the RAT can and cannot do is part of preparedness. By knowing the limitations, pilots avoid being caught off guard by, say, the loss of autopilot or the heavier controls.
Conclusion
The Ram Air Turbine may be a last-ditch system, but it is enormously important for safety. Most passengers have no idea it exists, yet their lives can depend on it.
The vast majority of pilots will not experience a RAT deployment mid-flight, but they must still be prepared for the off-chance they do end up using it.