Understanding the Airplane RAT – Ram Air Turbines Explained

What is a Ram Air Turbine (RAT)?

A Ram Air Turbine, or RAT, is a small but vital emergency power system installed in most modern aircraft. Picture it as a miniature wind turbine, tucked away in the fuselage or wing, that serves as a final lifeline when all primary and auxiliary power systems fail.

When deployed, this propeller-like device drops into the airstream, where the aircraft’s speed forces its blades to spin. This rotation captures the air’s kinetic energy through ram pressure, which the RAT then converts into either hydraulic pressure or electrical power.

While the power it generates is limited, it’s just enough to operate the most essential systems, enabling the crew to guide the aircraft to a safe landing. These critical systems include:

• Vital flight controls

• Key navigation instruments

• Communication equipment

On some aircraft, the system goes by another name: the air-driven generator (ADG).

How Does a RAT Work?

A RAT’s operation is elegantly simple yet highly reliable. It activates the moment an aircraft suffers a catastrophic loss of both primary and auxiliary power.

This rapid rotation drives a gearbox, converting mechanical energy into usable power for an electrical generator, a hydraulic pump, or both. The generator keeps essential flight instruments and communication systems online, while the hydraulic pump maintains the pressure needed for vital flight controls, such as the ailerons, rudder, and elevators.

RAT Deployment Process

The deployment of a Ram Air Turbine is a carefully orchestrated event, triggered either automatically by the aircraft’s systems or manually by the flight crew. In the most common scenario, onboard sensors detect a complete power loss from the main engines and the auxiliary power unit (APU), prompting the flight management system to command an automatic deployment. Alternatively, pilots can deploy it manually via a switch in the cockpit, providing a final layer of control in unexpected emergencies.

Tucked away inside a compartment in the fuselage or wing to preserve the aircraft’s aerodynamics, the RAT is held in place by a secure lock. When the deployment command is given, this lock is released. Instantly, a combination of spring force and gravity pushes the unit out into the slipstream below the aircraft. The entire sequence is nearly instantaneous—often completed in just a few seconds—because any delay could compromise the crew’s ability to maintain control.

Once exposed to the powerful airflow, the RAT’s propeller blades immediately begin to spin, often creating a distinct buzzing or whirring sound audible in the cabin. This rapid activation ensures uninterrupted power flows to critical flight controls and cockpit displays, equipping pilots with the essential tools to manage the emergency and execute a safe landing.

Rats in Military Aircraft

In military aviation, the loss of power is more than an emergency—it’s a critical vulnerability that can compromise a mission and endanger the pilot. While Ram Air Turbines serve the same fundamental purpose as their civilian counterparts, their role in combat aircraft is amplified by the unforgiving nature of operational scenarios. A RAT provides a lifeline, ensuring a pilot can maintain control of their aircraft even after sustaining damage or experiencing a catastrophic system failure in hostile territory. This capability is essential for pilot survival, mission continuity, and the recovery of a high-value asset.

Unlike commercial airliners, military jets depend on sophisticated fly-by-wire systems, advanced avionics, and power-hungry weapons displays. Should primary and backup generators fail, the RAT deploys to power these core functions. It ensures the pilot can continue operating the flight controls, see critical data on their heads-up display (HUD), and manage essential systems, allowing them to navigate away from a threat and attempt a controlled landing—turning a potentially fatal situation into a recoverable one.

Military Rats are designed to withstand harsh operating environments. They are compact, exceptionally robust, and engineered for flawless deployment under extreme G-forces and high airspeeds. The power generated is strictly for the bare essentials; no energy is wasted on non-critical systems. The ultimate goal is simple: give the pilot a fighting chance to fly the aircraft out of danger, making the RAT an indispensable last stand against a total loss of control.

Civilian Airliner Usage of Rats

In commercial aviation, passenger safety is the absolute priority. When a RAT deploys, it energizes only the most critical systems. Power is carefully prioritized: a single hydraulic circuit for primary flight controls might be active, along with essential instruments, while non-essential systems like cabin lighting and in-flight entertainment go dark.

Modern airliners with their complex fly-by-wire systems are especially dependent on this emergency power. The Airbus A380, for instance, features one of the largest Rats ever fitted to a commercial aircraft, with a propeller diameter of 1.63 meters (5.3 ft). This powerful unit is essential for generating sufficient hydraulic and electrical power for the massive aircraft’s control surfaces. Stowed neatly in the wing root or fuselage, the RAT acts as a silent guardian, underscoring the multi-layered safety philosophy of modern aircraft design and ensuring power is available in even the most improbable scenarios.

Notable Incidents Involving RAT Deployment

Real-world emergencies demonstrate the RAT’s critical value where it has proven to be a literal lifesaver. Two incidents, in particular, stand out:

Air Canada Flight 143 in 1983 provides one of the most famous examples Air Canada Flight 143 in 1983, an event that earned the Boeing 767 the nickname “Gigli Glider.” After running out of fuel mid-flight at 41,000 feet, the aircraft lost power from both engines, silencing the cockpit. The RAT deployed automatically, providing essential hydraulic pressure to the flight controls. This crucial power allowed the pilots to guide the massive, powerless airliner to a successful landing at a former air force base in Gigli, Manitoba, saving all 69 people on board.

The 2009 “Miracle on the Hudson” provides another dramatic example. After a bird strike caused dual engine failure on US Airways Flight 1549, an Airbus A320, the RAT deployed as the engines went silent. This was vital for the fly-by-wire aircraft, giving Captain Chesley “Sully” Sullenberger the control authority he needed to ditch the plane in the Hudson River, saving all 155 people aboard.

Power Output and Efficiency of Rats

A RAT’s power output is directly tied to the aircraft’s speed—the faster the plane moves, the more energy it can produce. For large commercial aircraft, this output typically ranges from 5 to 70 kilowatts (kW), while smaller units on low-airspeed models might generate around 400 watts.

Conclusion: The Importance of Rats in Aviation Safety

In aviation, the Ram Air Turbine exemplifies redundant engineering. Though rarely used, it is the final defense against a catastrophic loss of primary and auxiliary power, waiting silently for a moment pilots hope never comes.

From civilian airliners to military jets, the RAT provides a crucial safety net. Real-world incidents have proven its worth, turning potential disasters into remarkable stories of survival. The RAT represents more than emergency equipment—it embodies the aviation industry’s unwavering commitment to safety.