Which aircraft category cannot be type certificated in more than one category?

The category of aircraft that cannot be type certificated in more than one category is the commuter category. This is primarily because the commuter category is specifically defined for aircraft used in commuter operations that typically have a specific configuration or operational limitations associated with small passenger air transport. The regulations governing commuter aircraft are distinct and emphasize safety, reliability, and efficiency for this particular use, which sets it apart from other categories.

In contrast, the other categories—acrobatic, utility, and normal—have more flexible definitions that allow for varying uses and can often overlap. For example, a normal category aircraft can be designed to also serve as a utility aircraft, with certain limitations in place regarding operations like carrying passengers or cargo. Similarly, acrobatic aircraft are defined for specific maneuvers but can still fall into other categories depending on their design and intended use. Thus, the commuter category's specialized nature restricts it from being certified under more than one category.