According to NFPA 403, aircraft categories at airports are based on what primary criterion?

The correct answer, which identifies overall length as the primary criterion for categorizing aircraft at airports according to NFPA 403, is based on the specific guidelines set forth by the National Fire Protection Association. This categorization is crucial for ensuring that response plans and firefighting resources are tailored appropriately to the size and scale of the aircraft being dealt with in emergency situations.

Overall length, as a measurement, serves as a practical and effective standard, as it correlates with the aircraft's potential fire risk and the necessary firefighting resources that must be available for a swift response. Larger aircraft tend to have more complex structures and systems, which can influence the complexity and severity of incidents, making overall length a reliable indicator for determining the necessary response capability.

Other criteria, while relevant in various contexts, do not provide the same level of direct applicability for establishing response frameworks at airports. Factors such as total number of passengers, fuselage width, and fuel capacity, while important for understanding aircraft operation and safety, do not specifically guide the categorization necessary for emergency procedures as effectively as overall length does. Therefore, overall length becomes the primary measure for categorizing aircraft in the context of airport firefighting and emergency response planning.