Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace and can provide advisory services to aircraft in non-controlled airspace from the air traffic control tower.
Purpose of Air traffic control
The primary purpose of ATC worldwide is to prevent collisions, organize and expedite the flow of air traffic, and provide information and other support for pilots.
Air traffic controllers monitor the location of aircraft in their assigned airspace by radar and communicate with the pilots by radio. To prevent collisions, ATC enforces traffic separation rules, which ensure each aircraft maintains a minimum amount of empty space around it at all times.
In many countries, ATC provides services to all private, military, and commercial aircraft operating within its airspace. Depending on the type of flight and the class of airspace, ATC may issue instructions that pilots are required to obey or advisories (known as flight information in some countries) that pilots may, at their discretion, disregard.
The pilot in command is the final authority for the safe operation of the aircraft and may, in an emergency, deviate from ATC instructions to the extent required to maintain the safe operation of the aircraft.
Air traffic control towers have angled glass for a reason. Have you ever noticed that every air traffic control tower has angled windows? Windows in these towers have to be angled at precisely 15 degrees to decrease reflections and glare.
Air traffic controllers monitor the location of aircraft in their assigned airspace by radar and communicate with the pilots by radio. To prevent collisions, ATC enforces traffic separation rules, which ensure each aircraft maintains a minimum amount of empty space around it at all times.
Traffic elements
The elements that make up the air traffic control system must provide the capability to assist aircraft in traveling between airports as well as in landing and taking off.
1- Air Route
Air route traffic control centers are responsible for controlling and monitoring movement between origin and destination airports.
Each center is responsible for a defined geographic area; as an aircraft continues on a flight, crossing these areas, the responsibility for monitoring the plane is transferred (“handed off”) to the next air route center.
The flight continues to be transferred until it reaches the control area at its destination. At this point, typically within five miles of the destination airport, the air traffic control function is turned over to an airport controller, and the plane is guided through a sequence of locations in order to land.
As part of an overall objective to maintain safe and efficient air traffic flow, the pilot is required to comply with requests and instructions directed to him by the controller, subject to the pilot’s ultimate responsibility for the safety of the aircraft.
2- aids to navigation
Aids to navigation are a critical element in the air traffic control system. The navigation function needs to be satisfied by a variety of technologies to supplement destination findings when visual references are limited by weather or ambient light.
The earliest navigation aids were lighted beacons along the ground; these suffered obvious problems during adverse weather and were replaced by radio direction-finding equipment. Radio technologies are able to transmit the heading and distance to an intended destination.
Major commercial jets are now supplied with inertial navigation units, which allow an aircraft to independently navigate to a destination. A computer and gyroscope are used to sense direction and, with speed sensors, track direction and distance to the destination.
The navigation units can fly virtually automatically until in the vicinity of an airport, at which time the pilot and controller interact to safely control the landing.
The landing aids most often employed are illustrated An aircraft leaves the holding stack (a series of elliptical patterns flown at assigned altitudes while awaiting clearance to land), if there is one, and approaches a runway through an outer and an inner marker.
Airport surveillance radar and approach lights are used to assist the pilot. The landing occurs on a runway that is designed to carry the impact load of the aircraft on landing.
An important role is played by exit taxiways in expeditiously clearing aircraft from the runway in order to allow another operation (either landing or takeoff). The electronic landing aids, approach lights, and exit taxiways should work as a system to safely land and clear the runway for another operation.
3- the ability to control and direct aircraft on the ground
The final element in the air traffic control system is the ability to control and direct aircraft on the ground. Guiding safely Arriving flights to a terminal, and departing flights to the proper runway.
For smaller airports, under satisfactory weather conditions, this can be done visually. Larger airports, need ground movement radar to track planes on the ground, just as in the air.
Part of an air traffic controller’s duties is to conduct this guidance of planes along taxiways and near terminals. Exacerbated ground movement problems in the United States by the hub-and-spoke network that has evolved for most carriers since deregulation in 1978.
Carriers now operate in and out of hub airports, which are the focal points of large numbers of flights. Waves of aircraft arrive tightly spaced in a narrow time window and depart similarly bunched. Passengers frequently reach their destinations by changing planes at the hub.
This allows airlines to minimize transfer times and schedule efficiently, but it can result in extreme ground delays when many aircraft exchange gate positions simultaneously.
Airlines generally resist attempts to move flights significantly from on-the-hour or half-hour departures because of a perception of passenger inconvenience. Expansion of hub-and-spoke operations will continue the pressure on ground operations.
What are items or equipment available in the Air traffic control tower?
- Two-way radio equipment to establish contact between Tower and aircraft subject to control, surveillance, and/or information service.
- Access to handling and command of equipment serving all lighting on the airfield, such as runway and taxi lighting, approach lighting, and traffic lighting.
- Telephone and direct landlines to establish communication with all adjacent control authorities, necessary for coordination and clearance needs.
- All necessary documents to ensure up-to-date aeronautical information assisting controllers and aviators in executing their job!
Why do some airports have two control towers?
Overall size of the airport, number of runways, runway layout, number of aircraft movements, and obstructed line of sight to certain areas of the airport are all reasons airports have more than one air traffic control tower.
I’ll use for example airport in Dallas/Ft. Worth to illustrate. Currently, DFW is the 2nd largest airport in the US in terms of land area, 4th busiest in terms of passengers in the US, and 11th globally.
Initially, DFW had a central control tower to control its 3 original runways.