What visual change occurs when a flight's position is frozen?

When a flight's position is frozen, the position symbol is transformed into an hourglass. This visual change indicates that the flight's data is paused and not currently updating. The hourglass serves as a clear indicator to controllers that while they can still see the aircraft's last reported position, they should not assume it is ongoing or moving until further data is available. This is crucial for air traffic management as it helps ensure situational awareness and can prevent misunderstandings about the flight's actual movement or intentions.

The other visual representations in the other answer choices do not accurately reflect what happens when a flight's position is frozen. For instance, the disappearance of the track symbol would imply that the flight can no longer be monitored, which is not the case when its position is merely frozen and still displayed. Similarly, the prominent display of Mode C is unrelated to the freezing of the flight’s position; it pertains to altitude information. Lastly, a track position that moves continuously contradicts the concept of a frozen position, as that would suggest live data updates which do not occur in that state.