What system is used only if the utility hydraulic system fails for lowering the landing gear?

The system used exclusively when the utility hydraulic system fails to lower the landing gear is referred to as the emergency hydraulic system. This system is specifically designed to provide an alternate means of lowering the landing gear in situations where the primary hydraulic system experiences a failure.

In aviation, the hydraulic system is crucial for operating various components of the aircraft, including the landing gear. If the primary utility system fails, the emergency hydraulic system activates to ensure that pilots can still safely land the aircraft by deploying the landing gear. This redundancy is vital for maintaining aircraft safety and operational reliability.

The main gear hydraulic override, while it may be involved in certain hydraulic system functions, does not serve as an emergency system for lowering the landing gear. The manual driver system can allow for manual operation of different mechanisms but is not specific to the emergency deployment of landing gear. Lastly, the nose gear manual extension refers specifically to the manual process for extending the nose gear but does not encompass the broader emergency system that affects all landing gear. Thus, the emergency hydraulic system is the correct choice as it is tailored for this exact scenario.