Which of the following is a characteristic of mechanical back-up?

In the context of mechanical back-up systems in an aircraft, the correct response focuses on how pitch control can be manually adjusted without relying on hydraulic systems. The manual trim wheel allows pilots to fine-tune the aircraft’s pitch attitude in a simplified manner, especially during situations where hydraulic power may be compromised or unavailable. This characteristic becomes particularly important for maintaining control under adverse conditions where primary systems may be failing or have limited functionality.

The manual trim wheel provides a direct mechanical means for pilots to adjust the elevator position, offering a practical solution to maintain desired flight parameters. This design feature highlights the redundancy built into aircraft systems, ensuring that, even without hydraulic assistance, pilots can still effectively manage pitch control.

While the other responses may contain aspects of aircraft control, they do not specifically align with the fundamental characteristics of mechanical back-up systems. For instance, lateral and roll control through the sidestick primarily relies on electronic signals and hydraulic systems, rather than mechanical inputs. Similarly, hydraulic power being unnecessary or sidestick autotrim functionality focusing exclusively on pitch does not pertain to the specific operation and advantages offered by the manual trim wheel in mechanical back-up.