Which regulation offers guidance on instrument range markings for aircraft certificated in the normal category?

The regulation that offers guidance on instrument range markings for aircraft certificated in the normal category is 14 CFR Part 23. This part of the Code of Federal Regulations specifically outlines the airworthiness standards for aircraft that fall under the normal category, which includes small general aviation aircraft.

Part 23 includes detailed requirements regarding various systems on these aircraft, including the operation and design of instruments. The regulations are focused on ensuring safety and performance in typical flying conditions, which is crucial for pilot operations and decision-making. Therefore, it provides specifications for how instruments should be marked, ensuring that pilots can easily read and interpret the information they need during flight operations.

In contrast, other parts mentioned, such as Part 21, primarily encompass the general requirements for the certification process, Part 25 pertains to transport category aircraft, and Part 27 deals with rules applicable to rotorcraft, such as helicopters. These do not specifically address the normal category aircraft, hence why they do not apply in this context concerning instrument range markings.