What does the suffix 'X' indicate regarding equipment compatibility of the selected aircraft?

The suffix 'X' is indicative of a specific configuration related to aircraft equipment compatibility, primarily noting the absence of certain equipment. When this suffix is present, it signifies that the aircraft does not have a transponder or Distance Measuring Equipment (DME) installed. This is an important distinction for air traffic control and operations because aircraft equipped with transponders and DME can communicate their position, altitude, and other critical information, thereby enhancing safety and situational awareness. Understanding this designation helps air traffic controllers assess the capabilities of an aircraft and determine the appropriate procedures for handling it within the airspace system.