In what context is the term "Untracked aircraft" used?

The term "Untracked aircraft" is primarily used in reference to Mode C Intruders. This includes aircraft that are not being positively identified on radar but are still operating in controlled airspace. Mode C refers to the aircraft's transponder mode that provides altitude information to air traffic control when the aircraft is outside the radar surveillance capability. In the context of airspace management, untracked aircraft pose a significant challenge for controllers as they require additional caution to ensure the safety of airspace by monitoring potential conflicts.

The consideration of Mode C Intruders is particularly important due to their altitude reporting capabilities, which allow controllers a limited ability to determine their position relative to other known traffic. Thus, identifying and dealing with untracked aircraft—especially those that may be intruding into airspace where they should not be—is critical for maintaining safe air traffic operations.

In contrast, the other options involve specific situations or categories of aircraft that may not encompass the broader definition applied to untracked aircraft. For example, holding patterns and VFR targets (Visual Flight Rules) typically involve aircraft that are either tracked or known to air traffic control, while emergency landings refer to a distinct situation requiring specific management protocols unrelated to the untracked status designation.