Which condition triggers the RAT deployment procedure?

Which condition triggers the RAT deployment procedure?

• A. Loss of cabin pressure
• B. Failure of one main power source
• C. Both main power sources fail
• D. When the aircraft is on the ground in standby mode

Answer: (C)

RAT deployment is triggered by a complete loss of primary power. The Ram Air Turbine automatically extends into the airstream to provide emergency hydraulic power to essential flight controls and critical systems when both main power sources fail. On the 787, the normal sources are the two engine-driven generators (with the APU generator available if needed). If both of these fail, there’s no power to operate the flight controls, so the RAT steps in to keep control possible and allow a safe return or landing. Losing cabin pressure is handled by oxygen systems, not the RAT. Losing only one main power source still has another source available, so RAT deployment isn’t required. On the ground in standby mode, RAT deployment isn’t triggered because there isn’t a complete flight-power loss.

RAT deployment is triggered by a complete loss of primary power. The Ram Air Turbine automatically extends into the airstream to provide emergency hydraulic power to essential flight controls and critical systems when both main power sources fail. On the 787, the normal sources are the two engine-driven generators (with the APU generator available if needed). If both of these fail, there’s no power to operate the flight controls, so the RAT steps in to keep control possible and allow a safe return or landing. Losing cabin pressure is handled by oxygen systems, not the RAT. Losing only one main power source still has another source available, so RAT deployment isn’t required. On the ground in standby mode, RAT deployment isn’t triggered because there isn’t a complete flight-power loss.