Which of the following is NOT a potential cause of a spongy feel in hydraulic controls?

A spongy feel in hydraulic controls typically indicates that there is an issue with the hydraulic fluid or the system itself, impacting the responsiveness and performance of the controls. The presence of air in the hydraulic system can create compressible pockets in the fluid, resulting in a spongy feel when controls are manipulated. Low fluid levels can also cause a lack of adequate hydraulic pressure, leading to a similar sensation. Additionally, a kink in the hydraulic line can obstruct fluid flow, resulting in a less effective control response.

Mechanical failure, though it could lead to other types of performance issues, does not directly cause a spongy feel in hydraulic controls. Instead, if there were a mechanical failure, one would likely encounter symptoms like a complete loss of control or irregular movements, rather than the soft compressibility associated with air or fluid issues. Therefore, the correct answer identifies mechanical failure as not contributing to a spongy feel in hydraulic controls, as it represents a different category of potential problems.