What is the function of the standby hydraulic system on a 737-800?

The standby hydraulic system on a 737-800 is designed to serve as a backup in the event that the primary hydraulic systems (system A and/or B) lose pressure. This redundancy is critical for ensuring the safety and continued operability of the aircraft. The standby system provides hydraulic pressure to essential flight control surfaces and systems, which may need to operate in case the primary systems fail. By having this backup system, the aircraft can maintain a level of control even if there is an issue with the primary hydraulic systems.

While the other options present functions that are important for different systems within the aircraft, they do not accurately describe the role of the standby system. The standby hydraulic system is not the main system for all controls, nor does it specifically power non-essential systems or generate pressure solely for the landing gear. Its primary purpose is to act as an auxiliary source of hydraulic pressure to maintain function and control, reinforcing its importance in overall aircraft safety.