I am sure all of us who love Radio communications are aware that both ships as well as aircraft across the world primarily use radio communications as a mode of ensuring that there is safe movements of passengers and cargo across the world from point to point. Although modern technologies like sattelite communications etc do play their role in keeping aircraft or ships moving safely, radio communications on VHF/HF is still the backbone of air/ocean traffic control operations. I have already published an article on ship traffic operations and so this article would focus on air traffic management.
The soft and relaxed voice from the ground has a soothing effect on the pilot who completes his tiring journey by making a successful landing. It's a wonder for many how an aircraft reaches its final destination from a departure station, who all are involved in the process of safe flight and landing ? It is understandable if they assume that the pilot is the person who takes care of everything from take off, enroute flying and landing. People in general know about the pilot, but much less about those who remain behind the screen and shoulder the responsibility of guiding the flights from the starting an engine at departure aerodrome to its landing at destination. 
The limited field of view from the pilot's cockpit limits pilot's ability to avoid any close proximity to other air traffic around him during the course of the flight as well as on the ground. He is, therefore, dependent on the Air Traffic Controller for directing him in his flight and on the ground for all manoeuvres right till the end of his journey.
To eliminate confusion in understanding a particular instruction, standard Radio Phraseologies have been laid down which are understood by the pilots and Air Traffic Controllers the world over. A small mistake by Air Traffic controller or a misunderstanding by a pilot can result in a disaster and the loss of many lives. While pilots are required to follow Controller's instructions faithfully and meticulously, Air traffic Controller ensures that the instructions given are clear and flawless.
Although globally there are private players you manage air traffic operations, in India strictly air traffic operations is under the control of Airports Authority of India who manage the entire civilian skies which India controls. Defence has their own Air Traffic operations primarily managed by the Indian Air Force.
Civilian Air traffic management across the country is executed through a network of control towers, navigational aids and beacon stations which are located both at airports as well as non airport locations across the country. The Radio communication part of its consists of three main components.
Control Towers - Any airport you see you cannot miss a tall oval building which rises above other structures in the airports and that essential is the control tower with which an aircraft contacts first before a pilot can start his engine. Then its the tower control which guides the aircraft till take off and upto say 5-10 nautical miles when its handed over to Radar.
Chennai Airport Tower Frequency : 118.100 MHZ
Approach Radar - Once taken off the aircraft then switches to another radio frequency which guides them till possibly approx 200 nautical miles from the takeoff location or to another ground control enroute to final destination airport. Once the aircraft nears the destination airport the process happens vice-versa with first approach radar controllers guiding the aircraft till visual sight of control tower and air traffic controllers guide the aircraft to land safely.
Chennai Airport Approach/Radar Frequency : 127.900 MHZ / 124.450MHZ
FIC Region - This is more at a global level where the whole world is divided into various Flight information regions and aircraft when they travel from say Asia to Europe pass through multiple FIC Region controls. Chennai is an FIC Region and has control upto near Singapore on the eastern side and many airports under its region.
Control Towers and Approach Radar operations use VHF communications for contacting aircrafts, whereas FIC's use HF for long distance communication.
If you are more interested to know about Air Traffic Control operations in India AirSpace , pls visit the Indian Air Traffic Controllers guild website which has plenty of info.
G.Vipin Shankar, SWL
