The Air Traffic Control (ATC) is a service provided to aircraft with a purpose of preventing collisions, organizing the flow of air traffic, providing information and other support to pilots. It issues instructions that the pilots are required to obey and also gives advisories or flight information to pilots. They must coordinate the movements of thousands of aircraft, keep them at safe distances from each other, direct them during take-off and landing from airports, direct them around bad weather and ensure that traffic flows smoothly with minimal delays.
The primary method of controlling the immediate airport environment is visual observation from the airport control tower, which is usually a tall, windowed structure located on the airport grounds. Air traffic controllers in the tower are responsible for the separation and efficient movement of aircraft and vehicles operating on the taxiways and runways of the airport itself, and aircraft in the air near the airport. ATC controllers use the workstations equipped with synthetic radar screens and consoles with the information on the aircrafts/ flights, which are currently under their jurisdiction, and those which are expected to be soon at the entry of their sector (or sectors) in the next half an hour.
There is a separation of responsibility inside the control tower:
- Ground control: Responsible for airport movement on the ground, such as on the taxiways, inactive runways, aprons and holding areas. Any aircraft, vehicle, or person walking or working in these areas is required to have clearance from ground control. This is normally done via radio, but there may be special cases where other procedures are used. Aircraft or vehicles without radios must respond to ATC instructions via light signals or else be led by vehicles with radios.
- Air control: Responsible for movement on the active runways. Air control clears aircraft for take-off or landing, ensuring that prescribed runway separation (keeping aircraft at a minimum distance from one another ensuring that they don’t collide) will exist at all times.
- Flight data and clearance delivery: Clearance delivery is the position that issues route clearances to aircraft, typically before they commence taxiing. Clearances contain details of the route that the aircraft is expected to fly after departure and also contains aerodrome information such as weather and airport conditions. It also gives landing clearances. Flight data gives information such as weather changes, outages at the airport, delays, runway closures, etc.
Not all airports have towers (called non-towered airports). At non-towered airports, instead of receiving instructions from an air traffic controller, pilots follow recommended operations and communications procedures for operating at an airport without a control tower.
Traffic flow is broadly divided into departures, arrivals, and overflights. As aircraft move in and out of the terminal airspace, they are handed off to the next appropriate control facility. The ATC also uses systems and protocols like secondary surveillance radar, surface movement radar (SMR), advance surface movement guidance and control system (ASMGCS), crew resource management (CRM) and ground movement planner (GMP), TRACON, to name a few, to assist in operations.
ATC provides services to aircraft in flight between airports as well. Pilots fly under one of two sets of rules for separation: visual flight rules (VFR) or instrument flight rules (IFR). Air traffic controllers have different responsibilities to aircraft operating under the different sets of rules.
In addition, an area control centre (ACC) also known as a centre or en-route centre, is a facility responsible for controlling aircraft flying in the airspace of a given Flight Information Region (FIR) at high altitudes between airport approaches and departures. As an aircraft reaches the boundary of a centre’s control area it is “handed off” or “handed over” to the next ACC. Centres also exercise control over traffic travelling over the world’s ocean areas.
The operation costs of ATC system consists of the expenses for maintaining the ground radio-navigation facilities and equipment, their depreciation, interest, operations and staff.
Author: Arjun Krishnan
Poster Credits: Tanish Shetty
Get to know us more at: