Imagine you’re at 35,000 feet, cruising along in a Boeing 787 Dreamliner. It’s quiet. Maybe you're watching a movie or picking at a tray of lukewarm pasta. Then, the unthinkable happens. Total power loss. Both engines go quiet, the lights flicker, and the glass cockpit displays start to go dark. In that split second, a small, propeller-like device drops from the belly of the aircraft.
It’s the 787 ram air turbine, or RAT.
Technically, it's the ultimate "break glass in case of emergency" tool. Pilots don't want to use it. Passengers don't want to see it. But without it, a "dead" airplane is just a multi-ton glider without a steering wheel. Most people think of the Dreamliner as a high-tech marvel of composite materials and lithium-ion batteries—and it is—but when the chips are down, it relies on a piece of technology that feels surprisingly old-school.
What exactly is a 787 ram air turbine anyway?
Basically, the RAT is a small wind turbine stored in a compartment under the fuselage. On the Boeing 787, it’s located near the right-hand landing gear wheel well. When the plane loses its main power sources—the engines and the APU (Auxiliary Power Unit)—this little fan drops into the airstream.
The rushing air spins the blades. This rotation generates two vital things: hydraulic pressure and electricity.
On the Dreamliner, things are a bit different than on older planes like the 767 or 747. The 787 is famously "more electric." It swapped out a lot of traditional pneumatic systems for electrical ones. This means the 787 ram air turbine has a massive job. It has to power the flight controls so the pilot can actually move the elevators, ailerons, and rudder. If those don't move, the plane doesn't fly; it just falls.
The 787's RAT is beefy. It’s designed by Collins Aerospace (formerly Hamilton Sundstrand), and it’s one of the most powerful units ever put on a commercial jet. It has to be. In an "all-engine-out" scenario, that tiny propeller is the only thing keeping the flight deck displays alive and the fly-by-wire system functioning.
The "More Electric" challenge of the Dreamliner
Most people don't realize how much the 787 changed the game for emergency power. On a traditional jet, you use "bleed air" from the engines to do things like de-ice wings or run air conditioning. The 787 killed that. It uses massive generators.
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So, when the 787 ram air turbine deploys, it isn't just a backup; it’s a lifeline for a complex computer network.
If the RAT fails to deploy, the pilots are left with a very limited battery life. We’re talking minutes. The RAT provides indefinite power as long as the plane has airspeed. It's a simple relationship: the faster the plane flies, the more power the turbine generates. However, there’s a catch. If the plane gets too slow, the turbine doesn't spin fast enough. This creates a terrifying "sweet spot" during landing where the pilots have to maintain enough speed to keep the RAT spinning, but not so much that they overshoot the runway.
Why it's not just a "propeller on a stick"
You might look at a photo of the RAT and think it looks like something off a Cessna. Honestly, that’s a mistake. The engineering behind the 787 ram air turbine is incredibly dense.
The blades are "governed." This means they change their pitch—the angle at which they hit the air—to maintain a constant RPM regardless of how fast the plane is going. If the plane is diving at 400 knots, the blades flatten out so they don't over-speed and explode. If the plane is slowing down for a final approach at 140 knots, the blades bite harder into the air to keep the generator turning.
How it actually deploys
There are a few ways the RAT comes out to play:
- Automatic: If both engines shut down in flight, the onboard computers realize the situation is dire and pop the door instantly.
- Manual: The pilots have a switch in the cockpit. If they see smoke or a total electrical bus failure, they can "blow" the RAT themselves.
- Gravity/Springs: It doesn't rely on a motor to open. It's usually held by a latch and forced out by a powerful spring or just gravity, ensuring it works even if there's zero electricity left in the airframe.
Real-world stakes: When the RAT saved the day
While there hasn't been a famous "all-engine-out" 787 incident (thankfully), we can look at its predecessors to see why this tech matters. Remember the "Gimli Glider"? In 1983, an Air Canada 767 ran out of fuel at 41,000 feet. The engines died. The cockpit went dark. The only reason Captain Robert Pearson could steer that plane to an abandoned airfield in Manitoba was the ram air turbine.
Without it, the controls would have been physically impossible to move.
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Then there’s the "Miracle on the Hudson." When Captain Chesley "Sully" Sullenberger hit those birds, both engines on the A320 failed. The RAT deployed. It gave him the flight control law he needed to flare the plane perfectly into the water. The 787 ram air turbine is the evolution of that exact technology, refined for an airplane that is essentially a flying server room.
Myths and misconceptions
People often ask, "Why don't we just use the RAT all the time to save fuel?"
Short answer: it’s incredibly "draggy."
Deploying the RAT is like sticking a giant parachute out the side of your car. It creates massive amounts of aerodynamic drag. In a fuel-starved emergency, you want to glide as far as possible. You only want the RAT out because you need the power, not because it's efficient. It’s also incredibly loud. If you’re ever on a plane and hear a low-pitched, roaring vibration that feels like a chainsaw is attached to the floorboards, and the engines are silent? That’s the RAT.
Another myth is that the RAT can power everything. It can't.
When the 787 ram air turbine is running, the plane enters a "load shedding" mode. The galley power is cut—no coffee for you. The reading lights go off. The in-flight entertainment dies. The system prioritizes the Captain’s primary flight display, the navigation radios, and the hydraulic actuators for the tail and wings. It’s about survival, not comfort.
Maintenance: The silent vigil
Since the RAT is rarely used, you’d think it just sits there and rots.
Actually, it's a huge part of the maintenance cycle. Mechanics have to perform "ground functional tests." They use a special hydraulic ground cart or an external motor to spin the turbine up and ensure it's producing the correct voltage and pressure.
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They also check the "deployment actuator." There have been cases in aviation history where a RAT door got stuck due to ice or a faulty latch. For the 787, Boeing and Collins Aerospace designed heaters and specific seal geometries to make sure that door opens even if the plane is encased in a layer of ice.
The future of emergency power
As we move toward even more electric aircraft (and eventually hybrid or electric propulsion), the role of the ram air turbine is changing. Some designers are looking at "solid-state" backups like massive hydrogen fuel cells or advanced solid-state batteries.
But for now, there’s something comforting about the 787 ram air turbine. In a world of software and invisible electrons, it’s a mechanical certainty. If the air is moving, the fan is spinning. If the fan is spinning, the pilot has a chance.
Actionable Insights for AvGeeks and Travelers
If you’re interested in the mechanical safety of the Dreamliner, here’s what you should know:
- Listen for the "Whirr": On some 787 flights, during a heavy maintenance check or a ferry flight, you might hear a distinct hum. Usually, though, you'll never hear it in commercial service unless there's a serious problem.
- Spot the Door: Next time you're boarding a 787, look at the underside of the fuselage, just aft of the right-wing root. You'll see a small, rectangular panel. That’s the "life-saver door."
- Trust the Redundancy: The 787 has multiple layers of power—main engines, the APU in the tail, large lithium-ion batteries, and finally, the RAT. It’s a quadruple-redundant system.
- Check the Logs: If you’re a pilot or technician, always ensure the RAT safety pin is removed before flight (it sounds obvious, but "human factors" are real).
The 787 is a masterpiece of modern engineering, but it’s the 19th-century physics of a spinning blade in the wind that remains its final line of defense. It’s a perfect marriage of the old world and the new.
Next time you see a 787, give a little nod to the belly of the beast. There’s a tiny wind turbine in there, waiting for a day its owners hope will never come. That’s the definition of a silent guardian.
Next Steps for Deep Diving into 787 Systems
To truly understand the Dreamliner's resilience, you should look into the Boeing 787 electrical distribution system (specifically the 235V AC architecture). Understanding how the RAT integrates with the four main starter-generators provides a complete picture of how the aircraft manages a "total dark" scenario. You can also research the Collins Aerospace Aero-Mechanical systems documentation to see the specific RPM governors used in the 787's RAT assembly.