When an aircraft is at a higher altitude and greater airspeed, what must be allowed for?

When an aircraft operates at a higher altitude and greater airspeed, it's crucial to allow for increased compliance time and distance. This is because the aircraft's speed affects the time it takes to reach a specific point along its route, as well as the distances that must be managed for separation and spacing.

At higher speeds, the aircraft covers more ground in a shorter period, which requires air traffic controllers to provide more precise spacing and timing between aircraft to ensure safety and efficiency in their flight paths. Additionally, the increased altitude can also affect the aircraft's performance and flight characteristics, necessitating closer attention to navigation and compliance with air traffic control instructions.

In contrast, the other options may be features of operations but are not the primary considerations in this scenario. For instance, while fuel consumption could increase with speed, it is not the direct focus of managing compliance times. Similarly, radar range may not decrease with altitude; in fact, often aircraft at higher altitudes have improved radar coverage. Communication with air traffic control is essential, but the specifics of altitude and speed primarily relate to compliance requirements regarding time and distance.