In a failed primary hydraulic system scenario, which system might still be functional?

In a failed primary hydraulic system scenario, the emergency hydraulic system is designed to provide an alternate source of hydraulic power to critical flight control surfaces and systems. This redundancy ensures that, even if the primary system experiences a failure, pilots still have control over the aircraft and can safely manage situations that may arise from that failure.

The emergency hydraulic system is specifically engineered to engage automatically or manually, depending on the aircraft design, and can provide sufficient pressure to maintain essential functions such as landing gear operation and control of surfaces when needed. This system is a crucial safety feature in aviation, providing a backup that ensures continued operability of the aircraft's control systems.

Other options focus on systems that do not directly provide backup hydraulic support for flight controls. The primary flight control system relies on the primary hydraulic system for operation. The auxiliary hydraulic system typically supports other non-critical operations but is not the main backup for the primary systems. The environmental control system, meanwhile, is not reliant on hydraulic power and operates under other principles. Thus, the emergency hydraulic system stands out as the key option that remains functional in the event of a primary hydraulic system failure.