Air traffic flow management
Encyclopedia
Air Traffic Flow Management (usually seen abbreviated as ATFM) is the regulation of air traffic in order to avoid exceeding airport
or air traffic control
capacity in handling traffic, and to ensure that available capacity is used efficiently.
s available, layout of taxi tracks, availability of air traffic control, and current or anticipated weather
. Especially the weather can cause large variations in capacity because strong winds may limit the number of runways available, and poor visibility may necessitate increases in separation between aircraft.
Air traffic control can also be limiting, there are only so many aircraft an air traffic control unit can safely handle. Staff shortages, radar maintenance or equipment faults can lower the capacity of a unit. This can affect both airport air traffic control as well as en-route air traffic control centers.
When an air traffic control unit that will control a flight reaches capacity, arriving aircraft are directed towards holding patterns
where they circle until it is their turn to land. Because aircraft flying in circles is an inefficient and costly way of delaying aircraft, it is preferable to keep them on the ground at their place of departure, called a ground delay program
. This way, the delay can be waited out on the ground with engines off, saving considerable amounts of fuel. Obviously, careful calculation of en route time for each flight (and the effect of current wind upon it) and traffic flow as a whole is needed, which is highly dependent on computer
s.
s are tracked by a CFMU (Central Flow Management Unit). Each airport and air traffic control sector has a published maximum capacity. When capacity is exceeded, measures are taken to reduce the traffic. This is termed regulation. The aim is to utilize capacity effectively, keeping the average delay as low as possible, while ensuring capacity is not exceeded.
As a (highly simplified) example, if two flights are scheduled to arrive at an airport at exactly the same time, and the airport can handle one aircraft every 5 minutes, the aircraft may be assigned delays to ensure that the second aircraft arrives 5 minutes after the first. Similarly, the first aircraft will be required to depart on schedule and not allowed to depart late. This way, the second aircraft will not need to wait in the air.
In practice, the process is much more complex and highly computerized. One aircraft may be subject to several regulations at the same time. For example, a flight from Amsterdam
to Paris
may be regulated both by limited capacity at Paris as well as by limited capacity in Belgian
airspace.
In some cases, it may be possible to avoid delay by taking a different route. For instance, if Belgian airspace was the only regulation for the flight in the previous example, changing the route to avoid Belgium and going via Germany
instead might allow a flight to depart without delay, although the route might be a bit longer. In many cases, airlines authorize the CFMU to make changes in a flight's route to avoid delay.
Certain flights are exempt from regulation, for instance time-critical flights carrying human
organ
s for organ transplant
ation. If such flights are scheduled, regular traffic will be delayed instead.
If an airport is completely closed unexpectedly (for instance, because the only runway is blocked), a zero rate may be set for a certain time period (e.g. until the runway is expected to be reopened), which will cause all inbound flights to be issued a delay that will cause them to arrive after the reopening time. Flights already en route would either enter the holding or divert to an alternate airport.
to integrate the aircraft into the other traffic.
If a slot is missed (or if it is already certain in advance that it will be missed), CFMU assigns a new one. A different aircraft which has a slot because of the same regulation may be issued an improvement on its slot to make use of the newly available capacity. The slot and any revisions are communicated to the aircraft operator as well as the air traffic control unit at the departure airport via a special network called AFTN
.
It is perhaps surprising to some, that a delay in Istanbul may be incurred because inclement weather is expected at the destination in London, 3 hours later, even though the weather in Istanbul is good and there is no congestion. Blaming a delay on the departure airport or the airline is often not correct. Capacity limitations of the airspace between the two aerodrome
s, in the en-route segment, can also be a reason for delays.
Airport
An airport is a location where aircraft such as fixed-wing aircraft, helicopters, and blimps take off and land. Aircraft may be stored or maintained at an airport...
or air traffic control
Air traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...
capacity in handling traffic, and to ensure that available capacity is used efficiently.
Reason for use
Because only one aircraft can land or depart from a runway at the same time, and because aircraft must be separated by a certain time to avoid collisions, every airport has a finite capacity; it can only safely handle so many aircraft per hour. This capacity depends on many factors, such as the number of runwayRunway
According to ICAO a runway is a "defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft." Runways may be a man-made surface or a natural surface .- Orientation and dimensions :Runways are named by a number between 01 and 36, which is generally one tenth...
s available, layout of taxi tracks, availability of air traffic control, and current or anticipated weather
Weather
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...
. Especially the weather can cause large variations in capacity because strong winds may limit the number of runways available, and poor visibility may necessitate increases in separation between aircraft.
Air traffic control can also be limiting, there are only so many aircraft an air traffic control unit can safely handle. Staff shortages, radar maintenance or equipment faults can lower the capacity of a unit. This can affect both airport air traffic control as well as en-route air traffic control centers.
Area Control Center
In air traffic control, an Area Control Center , also known as a Center, is a facility responsible for controlling instrument flight rules aircraft en route in a particular volume of airspace at high altitudes between airport approaches and departures...
When an air traffic control unit that will control a flight reaches capacity, arriving aircraft are directed towards holding patterns
Holding (aviation)
In aviation, holding is a maneuver designed to delay an aircraft already in flight while keeping it within a specified airspace.-Implementation:...
where they circle until it is their turn to land. Because aircraft flying in circles is an inefficient and costly way of delaying aircraft, it is preferable to keep them on the ground at their place of departure, called a ground delay program
Ground delay program
An Air Traffic Control Ground delay program or FAA Flow Control is a traffic flow initiative that is instituted by the Federal Aviation Administration in the United States Air Space System....
. This way, the delay can be waited out on the ground with engines off, saving considerable amounts of fuel. Obviously, careful calculation of en route time for each flight (and the effect of current wind upon it) and traffic flow as a whole is needed, which is highly dependent on computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
s.
Operation
All IFR flight planFlight plan
Flight plans are documents filed by pilots or a Flight Dispatcher with the local Civil Aviation Authority prior to departure...
s are tracked by a CFMU (Central Flow Management Unit). Each airport and air traffic control sector has a published maximum capacity. When capacity is exceeded, measures are taken to reduce the traffic. This is termed regulation. The aim is to utilize capacity effectively, keeping the average delay as low as possible, while ensuring capacity is not exceeded.
As a (highly simplified) example, if two flights are scheduled to arrive at an airport at exactly the same time, and the airport can handle one aircraft every 5 minutes, the aircraft may be assigned delays to ensure that the second aircraft arrives 5 minutes after the first. Similarly, the first aircraft will be required to depart on schedule and not allowed to depart late. This way, the second aircraft will not need to wait in the air.
In practice, the process is much more complex and highly computerized. One aircraft may be subject to several regulations at the same time. For example, a flight from Amsterdam
Amsterdam
Amsterdam is the largest city and the capital of the Netherlands. The current position of Amsterdam as capital city of the Kingdom of the Netherlands is governed by the constitution of August 24, 1815 and its successors. Amsterdam has a population of 783,364 within city limits, an urban population...
to Paris
Paris
Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...
may be regulated both by limited capacity at Paris as well as by limited capacity in Belgian
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
airspace.
In some cases, it may be possible to avoid delay by taking a different route. For instance, if Belgian airspace was the only regulation for the flight in the previous example, changing the route to avoid Belgium and going via Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
instead might allow a flight to depart without delay, although the route might be a bit longer. In many cases, airlines authorize the CFMU to make changes in a flight's route to avoid delay.
Certain flights are exempt from regulation, for instance time-critical flights carrying human
Human
Humans are the only living species in the Homo genus...
organ
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...
s for organ transplant
Organ transplant
Organ transplantation is the moving of an organ from one body to another or from a donor site on the patient's own body, for the purpose of replacing the recipient's damaged or absent organ. The emerging field of regenerative medicine is allowing scientists and engineers to create organs to be...
ation. If such flights are scheduled, regular traffic will be delayed instead.
If an airport is completely closed unexpectedly (for instance, because the only runway is blocked), a zero rate may be set for a certain time period (e.g. until the runway is expected to be reopened), which will cause all inbound flights to be issued a delay that will cause them to arrive after the reopening time. Flights already en route would either enter the holding or divert to an alternate airport.
Slot & Calculated Take-Off Time
The CFMU issues delays by means of a CTOT (Calculated Take-Off Time), also known as slot time or simply slot. The slot is actually a period of time within which take-off has to take place; in Europe (Eurocontrol) it is defined between −5 and + 10 minutes from CTOT. The aircraft is required to be at the runway, ready for departure at its CTOT, the leeway is for air traffic controlAir traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...
to integrate the aircraft into the other traffic.
If a slot is missed (or if it is already certain in advance that it will be missed), CFMU assigns a new one. A different aircraft which has a slot because of the same regulation may be issued an improvement on its slot to make use of the newly available capacity. The slot and any revisions are communicated to the aircraft operator as well as the air traffic control unit at the departure airport via a special network called AFTN
AFTN
The Aeronautical Fixed Telecommunication Network is a worldwide system of aeronautical fixed circuits provided, as part of the Aeronautical Fixed Service, for the exchange of messages and/or digital data between aeronautical fixed stations having the same or compatible communications characteristics...
.
It is perhaps surprising to some, that a delay in Istanbul may be incurred because inclement weather is expected at the destination in London, 3 hours later, even though the weather in Istanbul is good and there is no congestion. Blaming a delay on the departure airport or the airline is often not correct. Capacity limitations of the airspace between the two aerodrome
Aerodrome
An aerodrome, airdrome or airfield is a term for any location from which aircraft flight operations take place, regardless of whether they involve cargo, passengers or neither...
s, in the en-route segment, can also be a reason for delays.
External links / sources
- Metron Aviation
- Bay of Bengal Cooperative Air Traffic Flow Management SystemBay of Bengal Cooperative Air Traffic Flow Management SystemBay of Bengal Cooperative Air Traffic Flow Management System is the Air Traffic Flow Management of Asia.CFMU was launched in 2007 by the International Civil Aviation Organization and Aeronautical Radio of Thailand, Ltd ....
, BOBCAT - Eurocontrol CFMU Website
- FAA Air Traffic Control System Command Center home page