Air Traffic Control, as most of us understand,is the profession in which controllers provide the separation between aircraft so that they do not collide in the air. However, the task is much more complex than that. The main goal of Air Traffic Control (ATC) is the provision of ‘safe, orderly, and expeditious flow of air traffic’. Besides providing separation between aircraft on ground and in air,an ATC also needs to coordinate with units like Air Force, Airport Operator, Fire Services, District Administration etc. for smooth flow of air traffic.
As in a baton relay race, the baton is passed from one runner to the next in order to win the race, in ATC, an aircraft can be thought of a baton whose control is passed from one ATC unit to the other so that an aircraft can reach its destination safely and with the least delay. The relay starts with booking of a flight plan and ends when the aircraft switches the engines off at the destination.
ATC comes under the category of Air Traffic Services (ATS). So, to understand ATC, a brief idea of the objectives of ATS is needed. These objectives summarize all the work that is done by ATCOs (Air Traffic Control Officers) all around the world.
The objectives of the air traffic services is to:
- prevent collisions between aircraft;
- prevent collisions between aircraft on the maneuvering area and obstructions on that area;
- expedite and maintain an orderly flow of air traffic;
- provide advice and information useful for the safe and efficient conduct of flights;
- notify appropriate organizations regarding aircraft in need of search and rescue aid, and assist such organizations as required.
So let’s start unfolding Air Traffic Control step by step.
1. Submission of FPL (Flight Plan)
Flight Plan is a document which carries details about the flight e.g. Registration of the aircraft, Flight level at which she intends to fly, Route to be followed, Date of flight, Equipment carried by aircraft, departure and destination aerodromes (an Airport is known as aerodrome in ATC language) etc. A sample Flight Plan is attached.In case of a “controlled” aerodrome, the FPL is filed in the A.T.S. Reporting Office (ARO) at the aerodrome from where the flight is to take off. If it is “uncontrolled” e.g. some helicopter is to take off from some town not served by an aerodrome after an election rally, then the FPL is filed at the nearest controlled aerodrome. Here “controlled aerodrome” means the aerodrome where Air Traffic Services are provided to aircraft.
2. Addressing of FPL
If FPL(Flight Plan) is filed without any errors, then it is addressed by the ARO to all en-route ATC centres as well as Destination aerodrome so that all of them are well aware in advance to facilitate the aircraft. Once addressing is done, FPL is sent to the Communication section where it is transmitted to all the addressees.
3. Flight Information Centre(FIC) and Air Defence Clearance(ADC) No.
Once plan is booked then an FIC (Flight Information Centre) number i.e. a unique number is allotted to that particular aircraft flight which signifies the acceptance of the flight plan in the system. If the flight is a scheduled one e.g. Air India’s daily flight between Delhi and Mumbai, then the plan is automatically approvedby IAF (Indian Air Force). But in case of non-scheduled flight (say some special cargo flight to import Delhi Metro’s train coaches) then Air Defence Clearance (ADC) number is requested from IAF, so plan is forwarded to IAF’s Military Liaison Unit (MLU).
4. Engine Start-up
Once all the formalities regarding boarding of passengers and cargo are done and aircraft is ready, then the pilot will request the Air Traffic Control Officer (ATCO) for Push-back and start-up. Push-back means aircraft will be pushed backward from stand after disconnecting from aerobridge, using a tow tractor (as aircraft cannot push back herself). Start-up means permission to start the aircraft engine(s). Once approval is given by ATCO aircraft commences push-back and start-up procedures.
5. Taxi / Ground Control
After push back and engine start up is done, aircraft is ready to taxi (which means now she will be moving to the Runway for take-off). Pilot will request for route and taxi clearances now. The concerned ATCO issues the route clearance and assess the situation like how many other aircraft are taxing, which taxiway to be given to the aircraft so that it does not collide with other aircraft or other obstruction on the ground (Remember ATS objective #2?). Usually taxi is given up to the Runway holding point.
Runway Holding Position/Point: A point at safe distance from the runway so that aircraft taxing on ground does not possess threat for Arriving or Departing aircraft.
6. Take Off / Tower Control
Once the runway is clear and aircraft is ready for take-off, Tower controller advises the aircraft to enter the runway,line up and take off. Surface wind information is also passed along with the take-off clearance as it can be prove crucial during initial climb of the aircraft.
7. Approach Control (APP)
Once the aircraft is airborne, the tower controller hands over its control to the next control position known as Approach Control. Approach Controller now issues climb clearance to the aircraft up to a level under its jurisdiction subject to the traffic. Approach control is one of the toughest positions in ATC. It really tests one’s skills to separate aircraft that are climbing or descending within the “limited” jurisdiction and reaction time.
8. Area Control Centre (ACC)
Once the aircraft is about to reach the vertical limit of the jurisdiction of Approach, then it is handed over to next unit i.e. Area Control Centre. ACC is responsible to climb the aircraft to its final cruising level requested by the aircraft subject to separation standards. If the destination is beyond the lateral jurisdiction of the ACC, the Aircraft is handed over to next ACC.
9. Approach Control (APP)
When the aircraft is about to reach its destination, it is required to commence itsdescend.Once the aircraft is about to descend through the levels of vertical jurisdiction of ACC, the control of this particular aircraft is handed over to the destination approach unit. APP will further descend the aircraft and at the same time it will guide the aircraft to align with the Runway Centre-line.
10. Landing/ Tower Control
Once aircraft has descended sufficiently and is aligned with the runway centre-line, its control is passed to the destination aerodrome tower controller. Tower controller now issues the landing clearance if the runway is clear.The landing clearance comprises of two important things i.e. the runway number/designator on which aircraft is to land as well as the surface wind.
11. Ground Control
After the aircraft lands, it is asked to vacate the runway and contact ground controller. Ground controller now issues taxi clearance to the stand where aircraft will disembark the passengers.
Now, as they say “a picture is worth a thousand words”, I am summarizing the entire ATC process in a single picture:
So this is how the entire Air Traffic Controlling of a single flight is done. It requires immense efforts of “behind the scene heroes” who work 24*7 to ensure that you reach your destination safely. I hope you enjoyed my article.