Which facility type provides air traffic control services within controlled airspace during the en route phase?

The correct answer is the facility type that plays a crucial role in managing air traffic during the en route phase, particularly within controlled airspace. This facility is the Air Route Traffic Control Center (ARTCC). ARTCCs are responsible for providing air traffic control services to aircraft flying at high altitudes and across long distances, essentially overseeing the safe transit of aircraft between departure and destination airports while they are in the en route phase.

In controlled airspace, it is critical to have coordinated and organized air traffic management, which is precisely the role of ARTCCs. They ensure that aircraft are safely separated, provide instructions to pilots, and manage flight paths to avoid conflicts, which is especially important in the busy airspace found over large geographic areas.

Other facility types, while they have important roles in air traffic management, do not primarily focus on the en route phase within controlled airspace. For example, Air Traffic Control Towers (ATCT) manage traffic in the immediate vicinity of airports during takeoff and landing. Flight Service Stations (FSS) assist with flight planning and provide weather information but do not control air traffic. Control Zones (CTR) are specific airspace areas around airports, often under the jurisdiction of ATCTs rather than ARTCCs