Which type of flight route involves restricted flight paths?

The type of flight route that specifically involves restricted flight paths is known as a restricted flight route. These routes are designated for use under particular conditions and typically impose limitations on who can fly in that airspace, as well as when and how they can do so. Restricted flight routes may be established due to various factors, including the presence of military operations, airspace management requirements, or safety concerns related to environmental hazards.

In contrast, flight corridors are generally designed to allow for safe navigation through busy airspace and are less restrictive. Flight axes represent broader paths for flight operations but do not necessarily imply restrictions. Open flight routes are those with few or no limitations, allowing for greater flexibility in flight plans. Therefore, the unique characteristics of restricted flight routes make them the correct answer in this context.