What is the smallest size cable permitted in aircraft primary control systems?

In aircraft primary control systems, the standard minimum size for cables is 1/8 inch. This size is established to ensure adequate strength and reliability for the critical functions of flight control. Using cables that are too small could compromise the durability and safety of the control system, leading to potential failures during operation. A 1/8 inch cable strikes a balance between flexibility and structural integrity, allowing it to transmit the necessary forces while withstanding various operational stresses experienced during flight.

Considering other possible sizes like 1/4 inch or 3/16 inch, they may not meet the aircraft's design specifications for primary control systems. A 1/4 inch cable would be unnecessarily large and potentially add unwanted weight. Similarly, while a 3/16 inch cable is larger than the minimum required, it also does not fit within the established guidelines for primary controls, which clearly stipulate 1/8 inch as the acceptable minimum size for effective and safe operation. Thus, 1/8 inch is recognized as the smallest permissible size cable in this context.