What Is a Ram Air Turbine? The Little Propeller That Keeps a Jet Flying

A ram air turbine (RAT) is a small wind-driven turbine that deploys into an aircraft’s slipstream to provide emergency electrical or hydraulic power when the normal engine-driven and battery sources fail. Air rushing past the airframe spins its propeller, which drives a generator or pump — giving the crew enough power to keep flying and land safely.

Most of the airplanes you’ll train in don’t have one. So why should a student pilot care about a gadget that lives on jets? Because the ram air turbine is one of the cleanest examples in aviation of a single idea you’ll use on every flight you ever make: moving air carries energy, and a well-designed airplane always has a backup. Understand the RAT and you understand redundancy, windmilling, and why airliners almost never run completely out of power. Let’s walk through it the way a good instructor would, standing next to the airplane.

What is a ram air turbine?

A ram air turbine is a small turbine, driven by the air flowing past a moving aircraft, that generates emergency electrical or hydraulic power. It normally sits stowed inside the fuselage or wing root and deploys — drops out into the airstream — only when the airplane loses its primary power sources. The term “ram air” simply means air forced into an opening by the aircraft’s own forward motion, the same effect that drives your pitot tube and many cabin air systems.

Think of it as a wind turbine that lives in the belly of a jet, waiting for the day it’s needed. When normal generators and pumps quit, the RAT swings into the slipstream, its little propeller spins up in the rushing air, and that rotation becomes the power the crew needs to keep flying. The clever part is what it asks for: nothing from the engines, nothing from the fuel. It only needs the airplane to be moving through the air, which a flying airplane always is.

For a student pilot, the RAT is worth knowing not because you’ll operate one soon, but because it shows two fundamentals in their clearest form: redundancy and ram air energy. Every certificated airplane is built so the failure of one system doesn’t end the flight, and the RAT is the dramatic, visible version of that idea.

How does a ram air turbine work?

A ram air turbine works by converting the kinetic energy of the airstream into mechanical rotation, then into electrical or hydraulic power. When deployed, the aircraft’s forward speed forces air through the RAT’s small two- or multi-blade propeller. The spinning propeller turns a shaft connected to an electrical generator, a hydraulic pump, or both, supplying power to the systems wired to it.

The amount of power a RAT produces depends on airspeed — faster air means more energy to harvest, exactly like a windmill in a stronger breeze. To keep its output steady across a range of speeds, many RATs use a governor or variable-pitch blades that adjust blade angle as airspeed changes, the same governing idea behind a constant-speed propeller. This keeps the generator turning at a usable rate whether the airplane is descending fast or holding a slower glide.

You’ll notice the RAT borrows physics you already study as a private pilot. A propeller turned by passing air is just a windmilling propeller — the same thing that happens to a piston engine’s prop after a failure in flight. Bernoulli’s principle and simple momentum explain why moving air pushes on the angled blades and makes them spin. The RAT takes that everyday aerodynamics and puts it to work as an emergency power plant.

When does a ram air turbine deploy?

A ram air turbine deploys when the aircraft loses its normal sources of electrical or hydraulic power — most dramatically during a dual-engine failure or a complete loss of normal generator power. On many transport aircraft the RAT deploys automatically when sensors detect that condition, and the crew can also deploy it manually with a guarded switch. Once it’s out, it stays out until the aircraft is on the ground and serviced.

The trigger is loss of the primary system, not a routine event. In normal flight, engine-driven generators supply electrical power and engine-driven pumps supply hydraulic pressure, with batteries and accumulators as the first layer of backup. The RAT is a deeper layer — it comes into play when those normal and first-backup sources can no longer do the job, which is why a typical airline pilot may go an entire career without ever seeing one deploy for real.

Because deployment is a serious, generally one-way event, it isn’t done casually. The system is designed to act fast when it matters — getting power back to the crew within seconds — because in a dual-engine-failure scenario, every moment of lost control authority counts.

What does a ram air turbine power?

A ram air turbine powers the essential systems a crew needs to keep flying and land — primarily the critical flight instruments, key flight controls, and core avionics, depending on the aircraft. It is sized to run the essentials, not the entire airplane. The cabin lights, galley, and convenience systems go dark; the equipment that keeps the airplane controllable stays alive.

On aircraft with hydraulically powered flight controls, the RAT’s job is often to drive an emergency hydraulic pump so the crew retains the muscle to move the control surfaces. On others, it drives a generator that feeds the essential electrical bus — the instruments and avionics that let the pilots see attitude, airspeed, and altitude and talk to air traffic control. Some RATs do both, with the specific architecture varying by manufacturer and model.

The design philosophy is “enough to fly the airplane.” A pilot facing a dual-engine failure needs three things: to keep the airplane under control, to know what it’s doing, and to communicate. The RAT exists to protect exactly those capabilities while the crew works the emergency and sets up for the best landing they can make.

Which aircraft have a ram air turbine?

Ram air turbines are found on transport-category airliners and many business jets — aircraft large and fast enough that a wind-driven turbine is a practical emergency power source. Common examples include the Airbus A320, A330, and A350 families and the Boeing 757, 767, 777, and 787, along with numerous corporate jets. Light single-engine training airplanes do not carry them.

Why the split? It comes down to speed, size, and systems. Airliners cruise fast, fly high, and depend on electrical and hydraulic systems for their flight controls, so they need a power source that keeps working even with the engines out. A wind-driven turbine fits that bill perfectly. Lighter, slower airplanes meet the same redundancy goal with a simpler battery-and-alternator setup, which we’ll look at next.

Why don’t light training airplanes have a RAT?

Light training airplanes don’t have a ram air turbine because they don’t need one — they achieve the same redundancy with a simpler, lighter system. A typical trainer like a Cessna 172 has a battery and an engine-driven alternator (or generator) supplying electrical power, and its flight controls are operated directly by cables and pushrods rather than hydraulics, so it never depends on a power source to move the controls.

That’s the key difference. In a light airplane, you can fly with a totally dead electrical system — the engine keeps running on its self-powered magnetos, and you keep flying with your hands on the yoke and your feet on the rudders. You’d lose radios, some instruments, and electric flaps, but the airplane is still fully controllable. A RAT would add weight and complexity to solve a problem a light airplane doesn’t have.

So the RAT and your trainer’s battery-alternator system are really two answers to the same exam question: how do we make sure a single failure doesn’t take the airplane down? Once you see it that way, the RAT stops being an exotic jet curiosity and becomes a familiar idea scaled up to a faster, more system-dependent airplane.

If you want this kind of “how the whole airplane actually works” understanding before your checkride — systems explained so they finally click instead of being memorized — our Private Pilot Ground School walks through every aircraft system with cockpit-grade visuals, so you show up to lessons already understanding the machine.

The RAT in action: a dual-engine failure

Picture an airliner crew at a few thousand feet when both engines abruptly quit — the scenario every transport pilot trains for and almost never faces. In an instant, the engine-driven generators and pumps stop. The cockpit could go dark and the controls could stiffen. This is the exact moment the ram air turbine was built for, and on most modern airliners it deploys automatically within seconds, swinging into the slipstream and spinning up on the rushing air.

With the RAT supplying power, the picture changes. The essential flight instruments stay lit, the crew keeps the control authority they need, and the radios stay alive to declare an emergency and coordinate. The airplane is now a glider — but a controllable, instrumented glider, which is everything. The pilots can trim for best glide, pick the best available landing site, and fly a deliberate, stabilized approach instead of fighting a dead airplane.

This isn’t hypothetical. When US Airways Flight 1549 lost both engines to a bird strike after departing New York in 2009, its Airbus A320’s RAT deployed and helped power the airplane while the crew executed the now-famous landing on the Hudson River, with everyone aboard surviving. The RAT didn’t fly the airplane — the pilots did — but it gave them the power they needed to do their job.

Here’s the takeaway for a student pilot. You’ll likely never touch a RAT, but you’ll fly the same principle every time you go up: a moving airplane carries energy you can use, and good airmanship means always having a plan for when the primary system fails. “Calm as a skill” is what turns a frightening failure into a managed event — and a well-designed airplane gives a calm crew the tools to manage it.

PLT Study Guide

The FAA tags knowledge-test questions with PLT (Pilot Learning Statement) codes. These are the codes whose official FAA wording actually maps to the ram air turbine and the systems it backs up, translated into plain study points. (Note: the code sometimes paired with this topic — PLT250, about fuel types, characteristics, contamination, fueling, and precautions — is about fuel handling and does not apply to a wind-driven emergency power source. Ignore it for this subject.)

PLT207 — Recall electrical system: components, operating principles, characteristics, static bonding and shielding.
Know how an aircraft electrical system is powered and backed up — from the engine-driven generator or alternator and battery in normal operation to emergency sources like a RAT. Understand the idea of an essential bus that keeps critical instruments and avionics alive when normal power is lost.

PLT107 — Recall aircraft alternator / generator system.
Understand how a generator or alternator turns mechanical rotation into electrical power. The RAT is the same concept driven by airflow instead of the engine: a spinning shaft turning a generator, which is exactly how your trainer’s engine-driven alternator works in normal flight.

PLT273 — Recall hydraulic systems: components, operating principles, characteristics.
On aircraft with hydraulically powered flight controls, the RAT often drives an emergency hydraulic pump so the crew keeps the pressure needed to move the control surfaces. Know what a hydraulic system does and why losing its pump pressure matters.

PLT114 — Recall aircraft design: construction / function.
Understand redundancy as a design principle — why aircraft carry backup power sources, and how the RAT fits into a layered system of generators, batteries, and emergency power. This is the big-picture “why it exists” code for the topic.

Frequently Asked Questions

FROM CHRIS

Understanding the ram air turbine isn’t about flying a jet tomorrow — it’s about seeing the principle underneath it. A moving airplane makes its own energy, and a well-built airplane always plans for the failure of its primary system. Carry that mindset into your own trainer: know your electrical backups, know what still works when the alternator quits, and fly every flight like a pilot who has a plan when the primary system lets go.

Throttle On!

Chris Palmer

Founder & Chief CFI, Angle of Attack — Two-Time Master Aviation Educator and Gold Seal CFI