Deployment of the RAT in actual flight operations signifies a cockpit crew has nearly run out of power-source options, usually because all engine-driven generators as well as the APU have become inoperative. With no electric power except for ship’s batteries, there is little energy left to operate the hydraulic or electrical systems necessary to move the flight controls and power critical systems.
The RAT is a small turbine connected to a support bracket that allows it to hang beneath the aircraft once it is deployed. RATs come in a variety of power options, including hydraulic, electric and hybrid, and include a variable-pitch propeller that normally faces into the slipstream to spin an internal electric generator or hydraulic pump. The propeller’s pitch varies in order to maintain a constant output from whichever device is connected.
A RAT remains invisible inside the belly of the aircraft until it’s needed. Deployment is normally automatic, triggered when other power sources drop below a specified threshold that varies by aircraft. Aircraft that use a RAT normally include a cockpit switch that allows the flight crew to manually open the tiny doors beneath the aircraft and deploy the turbine when they believe it is needed. Usually there is no upper speed limit at which the RAT may be deployed, but there is a low-speed operational limit, below which the RAT ceases producing a constant electric current o