Which information is captured in Block 18 of a flight strip?

Block 18 of a flight strip is specifically designated for capturing the actual time the aircraft passes over a designated fix or, if the flight is cancelled, will display a cancellation symbol. This serves as an essential reference for air traffic controllers, allowing them to track the progress of the flight against its planned route and timing. The actual time over fix is critical for maintaining situational awareness, managing air traffic effectively, and ensuring safety, as it helps controllers understand where the aircraft is at any given point during its flight.

In contrast, other options such as the next fix or coordination fix, proposed departure time, and altitude information in hundreds of feet pertain to other aspects of flight information that are documented in different sections of the flight strip, but not specifically in Block 18.