Final answer:
The smallest diameter cable depends on the specific regulations and requirements outlined in the certification of the airplane. The size can vary depending on the location and purpose of the cable. It is important to consult the specific aircraft manufacturer's documentation for accurate information.
Step-by-step explanation:
The smallest diameter cable that can be used in the primary control system of an airplane certificated under 14 CFR Part 23 depends on the specific regulations and requirements outlined in the certification. However, generally speaking, aircraft control cables can vary in diameter based on their location and purpose.
For example, the cables used in the primary flight control surfaces like the ailerons, elevators, and rudder, which require high load-bearing capacity, are generally larger in diameter compared to secondary control surfaces like flaps and trim tabs.
It is important to consult the specific aircraft manufacturer's documentation, such as the Aircraft Maintenance Manual (AMM) or the Type Certificate Data Sheet (TCDS), to determine the minimum diameter cable requirements for a particular airplane model.