Plastic Pilot

An old marine proverb says that rats leave the sinking ship. Strangely, this somehow applies to airliners as well. Keep cool, there are not rats on board, Ram Air Turbines, abbreviated RAT. But just as the rats of the proverbs, when the RAT gets out, situation on board is not so good.

Two forms of power are required to operate a modern jet: electric and hydraulic. Electricity is needed for all the flight computers, radios, pumps, controlling environment systems, lighting, and many other systems. If all generators on board are lost, the batteries can be used but for a relatively short time only.

Hydraulic power is used to move the control surfaces: rudder, elevator and ailerons. These in turn make the airplane change its course. Hydraulic is also used to extend or retract the landing gear and other important things.

Under normal circumstances, both electricity and hydraulic pressure are produced by generators and compressors run by the engines. In the very unlikely case of everything failing (generators, pumps or engines), the last option is the RAT…

This is like a propeller which is driven by the airflow. The turbine itself drives a generator or an hydraulic pump, making power available. In case of double engine failure however, the RAT will simply make the descent controllable, like in the famous Gimly glider accident.

So when the RAT is taken outside on an airship, it’s possibly sinking…

The picture on the right hand side is the RAT of a Boeing 757. The RATs are not deployed normally in flight because of the massive drag they generate. On some planes, the RAT deploys itself in case of power failure, and this lead to some discussions when the BA Boeing 777 crash-landed in Heathrow. It was not clear on the pictures if the RAT was deployed or not, and this would have been a sign double engine failure… and this detail was sufficient to start speculations.