Which of the following is not a category of GPS/RNAV equipment?

The classification of GPS and RNAV (Area Navigation) equipment is based on the specific functionalities and regulatory requirements they fulfill in aviation. The correct answer identifies a category that does not fall within the recognized classifications.

Tactical IFR Systems, while they play a role in certain navigation contexts, are not categorized as standard GPS/RNAV systems. These tactical systems often have a specific application in military contexts or unique operational situations rather than being general IFR navigation aids.

On the other hand, the categories mentioned in the other choices—Mission Enhancement System, Systems meeting Requirements for IFR flight, and PGU (Portable GPS Units)—are recognized as established classifications of GPS/RNAV equipment that serve essential roles in ensuring safe navigation and compliance with regulatory standards for IFR operations. Each of these categories includes systems designed for varying operational scopes, enhancing navigation capabilities or ensuring adherence to IFR flight protocols.

Understanding these classifications helps pilots and aviation personnel recognize what equipment is suitable for their specific needs and regulatory obligations.