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ATFCM General

Air Traffic Flow and Capacity Management (ATFCM) is a critical operational process in modern aviation that ensures the safe, orderly, and efficient flow of air traffic while preventing airspace or airport overload.

In general, ATFCM ensures that:

  • Too many aircraft do not enter the same airspace sector at the same time

  • Airport arrival and departure capacities are respected

  • Delays and congestion are minimised across the network

Airport Capacity

BecauseDue onlyto onelocal aircraftrestrictions can land or depart from a(e.g. runway atlayout), athe givenaerodrome time,capacity andis becauselimited aircraft must be separated byto a certain distancenumber or time to avoid collisions, every airport has a finite capacity; it can safely handle only so manyof aircraft per hour. Additionally,This certain factors, such as weather,capacity can influencevary airports'depending capacity.on different conditions (e.g. runway configuration, availability of approach types, weather or staffing). 

In overloads, traffic demand is higher than the aerodrome's capacity. Therefore, ATFCM aims to reduce the number of arriving/departing traffic to avoid the risk of overloads. 

Enroute Capacity

Every sector has a defined hourly capacity and/or an occupancy limit. These aim to keep traffic volume at a level which is workload in each sector. Sector capacity can also vary depending on certain conditions (e.g. weather) or certain sector combinations. 

Regulation

When capacity is exceeded, measures are taken to reduce the traffic. This is termed regulation. The goal of regulation is to use the available capacity effectively, keeping the average delay as low as possible. 

Regulation by CTOT

When the ATFCM system detects a possible overload at an aerodrome or enroute sector, a CTOT (Calculated Takeoff Time) will be calculated automatically. This allows for the delay departing traffic on the ground to a time window with less traffic. 

A CTOT is valid for -5 to +10 minutes. This means that an aircraft with a CTOT of 1010z is only allowed to take off between 1005z and 1020z. 

Regulation by Short-Term ATFCM Measures (ECFMP)

While CTOTs generally help to regulate traffic during possible overloads, short-term ATFCM measures allow further restricting traffic and reducing sector complexity. On the Vatsim network, short-term ATFCM measures are coordinated via the ECFMP network across all European VACCs. 

Typical short-term ATFCM measures are: 

  • Level-Capping
  • Re-Routings or mandatory routings
  • Minimum Departure Interval (MDI)
  • Average Departure Interval (ADI)
  • Miles-in-Trail Restrictions
  • Speed Adjustments
  • Ground Stops

The ATFCM system will automatically generate CTOTs at aerodromes where MDIs exist, reflecting the required spacing in minutes. This tries to offload the holding points for traffic affected by the MDI. 

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