Where would you look to find out if a specific airplane can be certified in more than one category?

To determine if a specific airplane can be certified in more than one category, the most reliable source is the Aircraft Specifications or Type Certificate Data Sheet. These documents provide detailed information about the aircraft's design, performance, and the categories under which it can be certified, such as normal, utility, acrobatic, etc.

The Type Certificate Data Sheet specifically lists the applicable regulations and any limitations pertaining to the aircraft's certifications, including any multipurpose designations or possible operational categories. This makes it the authoritative source for understanding the certification capabilities of the aircraft.

Other sources, although useful in different contexts, do not provide the specific details required for understanding the certification categories. The FAA's website can provide general information, but it might not contain the specific details for individual aircraft. The aircraft's maintenance logbook primarily documents maintenance and service history rather than certification status. Similarly, service bulletins offer updates and recommendations for the aircraft but do not address certification categories. Thus, the Type Certificate Data Sheet is the most direct and authoritative source for this information.