Air Traffic Management

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Air Traffic Management (ATM) plays the key role in strategically controlling commercial air traffic system. An air controller needs to pay attention to the different aspects such as the destinations, altitudes, speed and direction during the descent and approach of the aircraft. In order to ensure safety operations, a proper system is required to regulate and to guide the movements of the all controlled aircraft. The operations are carried out in accordance with the ATC procedures using the latest technology such as radars and radio navigation aids. Operating under IFR, the directions of air traffic controllers maintain the secure distances between the aircrafts. Aircrafts fly IFR for ensuring safety during the flight. For the operation of ATC, the sky is divided into many Flight Information Regions (FIR). Several different sectors are included into FIR and are supervised by the controllers: air route traffic control centre, airport traffic control tower and TRACON (Terminal Radar Approach CONtrol).


This project explains the brief operations carried out by the different controllers ensuring no collision and any other accidents for a safe flight. During each operation, the aircraft is handed off from one controller to the other i.e. from one state to the other making it little more complicated. We have used the concept of State-Space Minimization to reduce the complexity involved in going from one state to the other. This makes the system more efficient and could be implemented in less time. The other concept we are using is the queuing system. Queuing System and Timed Automaton together are responsible for the stacking of aircrafts, their arrival and departure. It has to maintain the queue and clear each aircraft as per their priority. The following section deals with the operations of each controller and how they maintain the safe flight and the proposed theory for the aircraft stacking.

Operation of ATM:

In the present world scenario, every single minute hundreds of aircrafts either arrive to or depart from the airport. For a safe flight, a common flight profile has to be followed, which is done with the help of some specific controllers. For an aircraft to begin it must obtain the weather information and accordingly a flight plan is filed. Upon receiving the departure clearance from the tower, the aircraft starts from the gate and must receive instructions from the airport's ground controller. The Ground Controller will instruct with the appropriate taxiway to takeoff from the runway. Up on receiving the departure clearance from the tower, the aircraft starts from the gate and must receive instructions from the airport's ground controller. The Ground Controller will instruct with the appropriate taxiway to takeoff from the runway.

R I = Radar Information P F = Preflight

I E = Information Exchange C to T = Clearance to Takeoff

A/C P = Aircraft Progress P D = Pilot's Discretion to takeoff

A S D Info Exchange = Altitude, Speed, Direction Info Exchange

S D W AT Exchange = Speed, Direction, Weather, Air Traffic Information Exchange

ARTCC = Air Route Traffic control center

The takeoff clearance is issued by the Local Controller. Few minutes after the takeoff, the pilot has to change the radio frequency and must contact the TRACON Zone. During the departure phase, the aircraft gets a clearance to a new altitude from the airport via an assigned heading. Now the aircraft is under the Center Controller into the en-route phase. The Center Controller then guides the pilot as the aircraft moves from sector to sector. This phase doesn't last more than a few minutes to many hours relying on the time to reach the destination airport. The decent phase starts when the aircraft reaches within approximately 150 miles of its destination airport. Nearly about 50 miles from the airport, the aircraft reaches the TRACON and hence continues with the approach phase of the aircraft. Again from the TRACON the aircraft is handed off to the Local Controller at the destination airport. And after the clearance from the Local Controller the pilot is instructed to change the radio frequency and the aircraft is safe to land and handed off electronically to the Ground Controller. The Ground Controller then directs the pilot across the taxiways to reach the destination gate.

Ground Controllers:

The taxiing of aircraft from the gates to take off runways and from landing runways to the gates is managed by the ground controllers. The person controlling the ground controller directs the pilot to push the aircraft back from the gate and thus the aircraft taxis to the runaway. While doing so, the ground radar tracks all the parameters of the aircraft ensuring that it doesn't exceed the active runway with ground vehicles. The radar Information (R I) is provided to the Aircraft. The pilot approaches the ground controller with the Preflight (P F) information. The instructions to the pilot are given through the radio, such as which way to taxi and the runway to be taken to take-off. This way the Information is exchanged (I E) between the Ground controller and the Pilot.

Another responsibility of the Ground Controllers is to protect the “critical areas”. The protected zones concentrate on:

* Localizer

* Glide Slope

* Precision approach critical areas (should we include more details on this????

As soon as the aircraft crosses the designated takeoff runway, the same information is provided to the local controller.

Local Controller:

Local Controllers are responsible to maintain the safe distances between the aircrafts as they take-off or are about to take-off. The Local Controller gets the aircraft Progress Information (A/C P) from the Ground controller and gets the control from it. Unless the local controller deems the flight to be safe, the final clearance to take-off (C to T) is not permitted. After the final clearance it's the Pilot's discretion to takeoff (P D). Taking the clearance, the aircraft is accelerated and leaves the ground. Once left from the ground, the local controller passes this information ie Aircraft's progress (A/C P) electronically to the departure control at the TRACON family. Another responsibility of the Local Controller is to safely sequence arrivals and departures. If in any case Local Controller finds any unsafe condition, a landing aircraft would be told to “go-around” and then re-sequenced into the landing pattern as per the terminal area controller. The Ground Control and the Local Control have to be always communicating and making sure, either one is aware of the operations which impact the taxiways, and work with the approach radar controllers to create “holes” or “gaps” while allowing the departing aircraft to take off or to allows the taxiing traffic to cross the runways.

TRACON (Terminal Radar Approach CONtrol or Departure Controller):

Terminal controllers play an important role while providing all ATC services within the airspace. They handle traffic which is in the proximity of 30 to 50 nautical miles (56 to 93 km) radius from the airport. This area includes many other busy airports where one single terminal control provides the service to all the airports. Depending on the factors like neighboring airports and terrain, the actual airspace boundaries and altitudes, speed, direction of the aircraft ( A S D Info Exchange) are assigned to a terminal control. The traffic flow includes departures, arrivals and overflights. Aircraft progress (A/C P) is handed off to the next control facility such as a control tower, an en-route control facility, or a bordering terminal approach control, when it starts moving in and out of the terminal airspace. Thus, the TRACON directs the transition of an aircraft from the en-route phase through to the approach phase into the destination airport within the TRACON space. There are more than one TRACON controllers in the TRACON viz:

* High altitude descent controller

* Low altitude descent controller

* Approach control

* Feeder control

An aircraft is directed between the two descent altitudes (low and high). The high controller first hands off the aircraft to the low altitude controller which then will hand off to the approach controller. The approach controller receives many such descending aircrafts heading towards the same destination airport and now it's the approach controller's responsibility to maintain the aircrafts into one line of air traffic, thereby, ensuring safe operation. As soon as the aircraft reaches about 50 miles outside the destination airport, an electronic transfer is performed by the approach controller and the aircraft is handed off to the Feeder control. Once the aircraft reaches within the airport's airspace, it is given off to the Local Controller which resides in the airport's airspace. And hence, the aircraft is no longer in control of the TRACON.

Air Route Traffic Control Centre (ARTCC):

After the aircraft leaves the TRACON area, it then enters into a sector of ARTCC, where two other air traffic controllers monitor the aircraft. Prior to entering the ARTCC, the radar associate controller receives the aircraft information anywhere from five to 30 minutes. Then the radar controller works with respect to the associate controller in the ARTCC. The radar associate controller is responsible for all air to ground communication, safety separations and thus maintain the activities with the other centers.

Then it's the centre controller's responsibility

* To provide the weather updates and the air-traffic information to the pilot.

* To give directions to the pilot with respect to the speed, altitude thereby, maintaining safe distance between the aircraft within their sector (S D W AT variations).

The controller would monitor the aircraft unless it leaves their sector and is then passed off to the other sectors controller.

Another controller, the radar hand off controller, follows the radar and associate radar controllers during the time of heavy traffic and hence maintains the smooth air-traffic flow. Thus, clearances and instructions for the aircraft are done by the En-route traffic, which are then complied by the pilot.

Proposed Application:

In 1, ARTCC is exchanging the Speed and direction of the flight with the flight pilot to ensure its having safe journey. The same two factors i.e. Speed and direction is also exchanged between TRACON zone and the pilot. According to the state space minimization, if two states reaching a state with the same event then the states can be clubbed. Here the TRACON and ARTCC are combined together as shown in the above diagram mentioned as DC. The state space minimized is as shown in 2

Fig 2: State space minimized Diagram

The Air Traffic at the airports have been a major concern in the near past as the civilian population started commuting through air transport more frequently. Constructing airports is a huge investment and a long process, so constructing new airports because of air traffic surge is the final option any country would look at. The best possible option is to make use of the existing resources at its best to provide better solutions in managing the Air traffic at peak times. At any point of time only one aircraft can land or depart from a runway. To avoid collision between aircrafts we should have certain time gap. Airports have a limitation on the number of flights to be handled in a period of time. This limitation varies based on different factors like number of runways available, availability of air traffic control, availability of taxi track and weather restrictions.

So at such times when an Air traffic control attains certain capacity, it may no longer assist the flights in providing the runway and hence the incoming flights are led to the holding patterns. The holding patterns are those where the aircrafts circle in the vicinity of the airport till they get their chance to land. 3 describes stack of holding patterns. .3 shows the current system and the proposed one where the new one has the increased capacity to stack the flights. The present system in airports have flight stacking with a height difference of 1000ft i.e. every 1000ft one aircraft will be circling until they get the clearance from the air traffic controller to land. In this system, for instance let us take flight stacking go up to the height of 12000ft, then the maximum stacking at any point of time is 12 flights.

To improve this factor we may have to reduce the height difference between flights to accommodate more flights but at the same time safety is given high priority. So how do we achieve it?

As in the 3 on the right, the proposed stacking, the height difference between the flights is reduced to 700 ft from 1000ft and all the flights which have entered the stack should maintain the same speed. Air traffic controller comes into picture here; flight's time of entry into the stack is a calculated entry as shown in the 3. The lateral distance ( X ) between the flights should be maintained at a constant distance, this can be achieved by maintaining constant speed. Therefore the flights have sufficient gap with respect to the height ( Y ) and lateral distance ( X ) between the flights and have enough degree of variations in these two parameters as shown in the .3

Efficiency Improved: For 12000 feet in the normal stacking it can pile 12 Aircrafts. In the proposed stacking we can pile 17 aircrafts. Therefore 41% of improvement is seen.

An improvisation on this can be achieved as shown in the 4 where we have two stacks of flights. The first one is called the entry stack and the other is the final stack. When ATC is at its peak operation and there are a lot of incoming flights it is advised to have two stacks than having just one. The advantage here is that it has double the capacity of flights in the stack than having one stack, so the airport can handle them one after the other.

The 4 shows two stacks; all the flights which are inbound to the airport enter the Entry stack. If there is a situation wherein there is a health emergency to a patient in the flight they can be given the privilege of landing as the next flight or if the flight is having less fuel and it cannot do more circles in the holding pattern they can be given the priority to land.

Timed Automaton:

The above learnt inbound aircraft queuing at the Airport is considered in coming up with a timed automata.

Considering there is a stack (queue) of size 5 and the airport has 2 runways. The flights willing to land can prefer any runway as they get free. The aircraft arrivals are of type A1, A2, A3, A4. If there is a weather hindrance it takes 5 minutes to land (A1). An emergency landing is required to take 2 minutes (A2). The normal operation of the flight to land will take 3 minutes (A3). If there is a ground clearance problem then it would take 4 minutes (A4).

With the above criteria's set, the event set will be ES = {Arrival (a), Departure from Runway 1 (R1), Departure from Runway 2 (R2)} = { a, R1, R2 }

State space = {Flight in Runway 1; 1: flight in the runway, 0: flight not in the runway,

Flight in Runway 2; 1: flight in the runway, 0: flight not in the runway,

Q = Stack size of Aircraft }. For example {1, 1, 2} indicates there is a flight in R1, flight in R2 and the queue or stack size is 2.

S = Aircraft landing time start, i e it is being serviced getting cleared from the stack.

a = arrival of flights, a1 = arrival of first flight, a2 = arrival of flight 2 and so on.

d = departure of flights, d1 = departure of flight 1, d2 = departure of flight 2 and so on.

E = Stack is full and is diverted to another airport nearby.

If the stack is filled completely and there is a flight willing to land then that flight is diverted to the nearest airport.

Let us have the schedule of flight arrival time, and what type of arrival it is as [1, A3] , [2,A3], [3,A3], [4,A2], [5,A1], [6,A4], [7,A1], [8,A1], [9,A3], [10,A3], [11,A3], [12,A3], [13,A3], [14,A3], [15,A3], [16,A3] then we can derive the Timed Automata as in 6.

Goals of the Project:

* Thus in this project we explained the Air traffic management system, its current operation. Based on the system, we implemented DES concept of State space minimization to reduce the redundancy in the system and make it efficient.

* In the dynamic queuing system of the In-bound aircrafts, made the system to be more efficient by stacking more flights in the stack rather than sending them to a different airport.

* Developed a timed automaton of the incoming flights at the airport and how is it serviced based on the type of the aircraft.

* The advantage is that we created an efficient aircraft stacking at the airport at the peak times and air traffic management system which is more efficient.

* The DES concepts of state space minimization and timed automaton are implemented; by this we are synchronizing the concept learnt in the class to that of the concept what we had to convey i.e. Air traffic management.


Tracking and directing the flights is a complex work as it is a 24/7 activity and involves thousands of flights at any point of time. Increase in Air traffic and travelers' security are major concerns and that's the reason lot of study is happening in increasing the capacity of air traffic management and developing decision making systems to improve the efficiency of Traffic management.