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How Does A Ram Air Turbine Work? – Simple Flying

Thousands of turbofan-powered airliners operate scheduled commercial flights every day. In the case of a loss of power, pilots can generally rely on a plane’s Auxiliary Power Unit (APU). However, aircraft manufacturers also need to mitigate for instances in which the APU also fails. For this purpose, aircraft are fitted with a Ram Air Turbine (RAT). But how exactly does this device function?

The Mitsubishi MRJ regional jet is seen here with its Ram Air Turbine deployed during a test flight. The RAT is visible at the aircraft’s nose. Photo: Chiyoda I via Wikimedia Commons

How does the RAT work?

An aircraft’s Ram Air Turbine is a small auxiliary propellor that it can deploy in the event of a power loss. It works by generating power from the airstream passing over it as the plane flies, causing the turbine to rotate. The turbine can be connected to a generator or a hydraulic pump. This way, it can help to power either an aircraft’s electrical or control systems.

According to Skybrary, these devices are typically located in compartments in an aircraft’s wings or fuselage. The amount of power that a RAT generates is dependent on the speed of the plane at the time of its usage. They work using the concept of ram pressure. The greater the speed of the aircraft, the more power the RAT will generate.

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Airbus A350 Ram Air Turbine
An Airbus A350 with its Ram Air Turbine deployed towards the rear of its belly. Photo: Laurent Errera via Wikimedia Commons

The RAT’s size will correspond to that of the aircraft to which it is attached. As such, it is unsurprising that, at 1.63 meters in diameter, the Airbus A380 has the largest RAT among contemporary airliners. A typical RAT will be around 80 centimeters wide, and can generate between 5 and 70 kW of power when called upon in an emergency.

RAT usage in emergencies – the ‘Gimli Glider’

There have been several incidents in which an aircraft’s RAT has been deployed to provide emergency power. In fact, Collins Aerospace reports that the device has saved as many as 1,700 lives across 16 documented incidents. Among the most famous of these was Air Canada flight 143. This domestic service ran out of fuel between Montreal and Edmonton in 1983.

China-Southern-London-A380-Suspension-Getty
The Airbus A380 has the largest Ram Air Turbine among modern airliners. Photo: Getty Images

The crew successfully glided the Boeing 767 down from 41,000 feet to make an emergency landing at RCAF Station Gimli in Manitoba. This led to the incident becoming known as the ‘Gimli Glider.’ Maneuvers performed by the crew before landing disrupted the airflow around the RAT. This further decreased its hydraulic power, making the aircraft harder to control. Despite this, the crew managed to land the aircraft with no fatalities and just 10 minor injuries among the 69 passengers and crew.

Famous 21st-century RAT deployments

The RAT was also deployed in a similar fuel exhaustion incident involving Air Transat flight 236 in 2001. In this instance, the Airbus A330 flying from Toronto to Lisbon glided for over 100 miles after running out of fuel over the Atlantic Ocean. It eventually landed safely at Lajes Airport in the Azores, with no fatalities and just 18 injuries among the 306 passengers and crew.

Boeing 757 Ram Air Turbine
The Ram Air Turbine on a Boeing 757. Photo: Swampfoot via Wikimedia Commons

An aircraft can also lose power as a result of other incidents, such as bird strikes. Perhaps the best-known bird strike in recent memory involved US Airways flight 1549 in 2009. In this instance, a departing Airbus A320 lost all power over New York after striking a flock of geese. In a stunning display of skill and bravery, pilots Chesley Sullenberger and Jeffrey Skiles successfully ditched the aircraft in the Hudson River following the engine failure. With no fatalities, the ditching was unprecedented, and became known as the ‘Miracle on the Hudson.’

Did you know about Ram Air Turbines? Have you ever seen one up close and personal? Let us know your thoughts and experiences in the comments!

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