A Ram Air Turbine (RAT) is a small component that generates power in case of an engine failure. While aircraft are equipped with an Auxiliary Power Unit (APU) to provide necessary power to critical systems in case of complete engine failure, the RAT offers an additional layer of safety.

RATs generate power by injecting ram pressure - that which is exerted on the aircraft due to its movement through the air. Ram pressure depends on the speed of the aircraft. A RAT is located in the aft underbelly of the aircraft and can be deployed through gravitational force.

With thousands of airliners carrying hundreds of thousands of passengers each day, safety is the utmost priority. This article explains the functions of the RAT and highlights some instances where it is used on commercial flights during emergency situations.

How does the RAT work?

An aircraft's Ram Air Turbine is a small auxiliary propellor that can be deployed 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 aircraft's speed, the more power the RAT will generate.

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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 during 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. Perhaps among the most famous of these was Air Canada Flight 143. This domestic service ran out of fuel between Montreal and Edmonton in 1983.

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 more challenging to control. Despite this, the crew managed to land the aircraft with no fatalities and just ten 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.

An aircraft can also lose power as a result of other incidents, such as bird strikes. One of, if not 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.

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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!

Sources Skybrary, Collins Aerospace