Clearance void times are used at airports where?

Clearance void times are implemented at airports where communications with aircraft are difficult until they are airborne and where there is no control tower present. This situation often occurs in uncontrolled airspace or at airports where there is limited communication capability, which can impede the ability to provide timely and effective air traffic control instructions.

In these circumstances, a clearance void time allows pilots to accept a clearance for departure but requires them to take off within a specified time. If they are unable to depart within that timeframe, they must contact ATC again for a new clearance. This procedure helps to ensure safety and maintain an orderly flow of air traffic in environments where real-time direct communication is tricky, such as those without a control tower.

The other options suggest conditions that do not directly relate to the need for clearance void times. Unpredictable weather, high traffic density, or the operation of flights solely under visual flight rules may present their own challenges, but they do not specifically necessitate clearance void times as a solution.