In relation to unpaired limited data blocks, what does the data block NOT contain?

In the context of unpaired limited data blocks, the data block is designed to convey essential surveillance information to air traffic controllers. Specifically, it includes details that are critical for managing aircraft position and altitude, which are vital for ensuring safe and efficient airspace operations.

The data block typically contains the beacon code, which is a unique identifier for each aircraft, and Mode C information, which provides the aircraft's altitude. It also includes altitude information directly, indicating the current vertical position of the aircraft in flight.

However, the data block does not include the aircraft callsign. This is primarily because unpaired limited data blocks focus on essential data for surveillance rather than communication purposes, where the callsign would be more applicable. The aircraft callsign is typically used in voice communication for clarity and identification but is not necessary for the basic situational awareness that unpaired limited data blocks are intended to provide.

Thus, the true characteristic of an unpaired limited data block is its omission of the aircraft callsign while including the more critical surveillance data.