Ever looked at a massive jet engine and wondered what happens if it just... stops? It’s the ultimate nightmare for anyone with a mild fear of flying. You’re at 35,000 feet, the hum of the turbines vanishes, and suddenly the cockpit goes dark. Well, not entirely dark. That’s because of a tiny, frantic piece of machinery hidden in the belly or the nose of the plane called the aircraft ram air turbine, or RAT.
Most people have no idea it exists. Pilots hope they never have to use it.
Basically, the RAT is a small wind turbine. Think of those giant white windmills you see on hillsides, then shrink one down to the size of a ceiling fan and tuck it inside a supersonic metal tube. When things go sideways—specifically, when a plane loses its primary and auxiliary power—this little guy drops out of the fuselage into the screaming 500 mph slipstream. It spins like crazy, generating just enough hydraulic pressure or electricity to keep the flight controls moving. It is the literal last line of defense.
How the RAT actually works when things get ugly
It’s all about kinetic energy. Usually, an airplane gets its power from the main engines. They turn generators and pump hydraulic fluid. If the engines quit, you’ve usually got an APU (Auxiliary Power Unit) in the tail, but even that can fail or run out of fuel. That’s when the aircraft ram air turbine earns its keep.
The deployment is violent. It’s not a gentle sliding door; it’s a spring-loaded or gravity-fed drop that happens in seconds. Once the blades hit the rushing air, they spin up to several thousand RPMs. This rotation drives a small hydraulic pump or an electric generator. You aren't getting enough juice to run the ovens in the galley or the in-flight movies. Forget about the reading lights. What you are getting is the ability for the pilot to move the elevators, the rudder, and the ailerons. Without the RAT, a modern fly-by-wire plane like an Airbus A320 would essentially become a very heavy, very expensive lawn dart because the pilot’s inputs wouldn't reach the control surfaces.
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Real life or death: The Gimli Glider and US Airways 1549
We aren't talking about theoretical safety here. This hardware has saved hundreds of lives. Take the famous case of "The Gimli Glider" in 1983. An Air Canada Boeing 767 ran out of fuel mid-flight because of a metric-to-imperial conversion error. Both engines died. The cockpit went silent. The pilots lost their main displays. But the RAT deployed. That tiny fan gave Captain Robert Pearson the hydraulic pressure he needed to steer that massive, fuel-less bird onto a converted racetrack in Gimli, Manitoba. Everyone survived.
Then there’s Captain "Sully" Sullenberger and the "Miracle on the Hudson." When those geese took out both engines of US Airways Flight 1549, the aircraft ram air turbine deployed automatically. It provided the electrical power needed for the flight control computers to remain active in "Alternate Law," allowing Sully to maintain precise control during the ditching. Without that backup power, the story of Flight 1549 might have had a much darker ending.
Why don't we just use batteries?
You might think, "Hey, it’s 2026, why aren't we just using massive Tesla-style batteries?"
Honestly, weight is the enemy of aviation. Batteries are heavy, they degrade, and they can catch fire (remember the 787 Dreamliner battery issues?). A RAT is relatively light, simple, and it works as long as the plane is moving through the air. It’s an elegant solution to a terrifying problem. As long as you have airspeed, you have power. It’s a beautifully simple conversion of the plane's forward momentum into life-saving energy.
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Maintenance and the "silent" test
Engineers at companies like Collins Aerospace (who make a huge chunk of the world's RATs) have to ensure these things work after sitting dormant for years. They are checked during heavy maintenance C-checks and D-checks. Mechanics will actually "swing" the RAT, deploying it on the ground using a ground test motor to spin it up without needing a 500 mph wind. It's a loud, whirring sound that echoes through the hangar, a reminder of the raw power it’s designed to harness.
There’s a bit of a misconception that the RAT can help the plane fly longer. It can't. In fact, it creates a lot of drag. It’s like sticking your hand out the window of a car at highway speeds, but magnified by a thousand. This drag actually makes the plane lose altitude slightly faster, but it’s a trade-off any pilot would make in a heartbeat to keep the controls responsive.
Technical nuances: AC vs. DC and Hydraulic pressure
Different planes use the aircraft ram air turbine differently.
- On an Airbus A330, the RAT primarily powers a green hydraulic circuit.
- On a Boeing 777, it’s more about providing electrical power to the flight control electronics.
- The size varies too. A CRJ-700 regional jet has a RAT that looks like a toy compared to the one found on a Boeing 747 or an Antonov 124.
The blades are also clever. They use a "governor" mechanism. If the plane is flying too fast, the blades would spin fast enough to explode from centrifugal force. To prevent this, the pitch of the blades changes automatically—twisting to bite less air as speed increases—keeping the RPM within a safe range. It’s mechanical genius that doesn't rely on a computer to think.
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What pilots think about it
Talk to any commercial pilot and they'll tell you the RAT is the ultimate "break glass in case of emergency" tool. During simulator training, "dual engine flameout" drills always involve checking for the RAT icon on the display. If it doesn't deploy automatically, there's a manual override. It's a heavy handle or a guarded switch. Pulling it is a "point of no return" moment. You know that if you’re looking at that little fan spinning outside your window, you’re having the worst day of your career. But you’re also glad it’s there.
Actionable insights for the curious or the nervous
If you're a nervous flier, knowing about the aircraft ram air turbine should actually make you feel better. It proves that aviation safety isn't just about "Plan A" or "Plan B." It’s about Plan C, D, and E.
- Next time you fly: Look at the underside of the fuselage near the wing roots or the nose. You might see a small, rectangular door with a "DO NOT PAINT" sign or specific markings. That's the RAT's home.
- Study the "Gimli Glider" incident: It’s the gold standard for understanding how pilots manage energy when everything goes dark.
- Check the specs: If you're an aviation geek, look up the "minimum deployment speed" for the RAT on your favorite aircraft. It’s usually around 120-140 knots. If you go slower than that, the fan stops spinning fast enough to help, which is why the final moments of an emergency landing are so critical.
The RAT is a reminder that even in an age of AI and complex software, sometimes the best way to save a life is with a simple wooden or composite blade spinning in the wind. It's the ultimate backup in a world that usually relies on batteries and wires.
Next Steps for Aviation Enthusiasts:
To truly understand the physics involved, research the concept of "Total Air Temperature" and how it relates to the energy harvestable by a turbine at high altitudes. You can also look into the specific deployment logic of the Boeing 787, which uses a more complex "Power Management System" to decide exactly when to drop the RAT compared to older, purely mechanical systems.