Which action implies that the standby hydraulic system is engaged?

• A. The LOW QUANTITY light turns off
• B. The hydraulic pressure stabilizes
• C. The STBY RUD switch is activated
• D. Normal operations are resumed

Answer: (C)

The action that implies the standby hydraulic system is engaged is the activation of the STBY RUD switch. When this switch is activated, it specifically indicates that the aircraft's standby hydraulic system is being utilized, allowing the system to take over control of essential functions when the primary hydraulic system fails or is not available. This is a critical safety measure to ensure that necessary control surfaces can still be operated even in the event of a hydraulic failure.

The other options, while related to the operation of hydraulic systems, do not directly indicate that the standby system is engaged. The LOW QUANTITY light turning off might suggest that a low fluid level issue has been resolved but does not imply engagement of the standby system. Similarly, hydraulic pressure stabilizing indicates consistent system performance but does not specify which hydraulic system is in operation. Finally, resuming normal operations suggests that everything is functioning correctly, but it does not denote that the standby system is actively in use.