What must be included in the SSI categories?

The inclusion of security plans and specifications for screening equipment in the SSI (Sensitive Security Information) categories is essential because this information directly relates to the security measures taken to protect passengers and aviation systems. By classifying these plans and specifications as SSI, it ensures that sensitive operational details are safeguarded from potential threats. This level of confidentiality helps prevent unauthorized individuals from gaining insights that could compromise airport security or the effectiveness of screening protocols.

The other options do not align with the nature of SSI categories as closely. Weather conditions for flights are generally considered public information and do not present a security threat if disclosed. Passenger complaint procedures, while important for customer service, do not have direct implications for security and are thus not categorized as SSI. Similarly, airport layout designs, while potentially sensitive, typically fall within a different domain of operational information rather than the specific security measures that SSI focuses on. Therefore, the specification of security plans and equipment is the most pertinent inclusion in the context of SSI categories.