System Wide Events: Guidance for Controllers

System Wide Events: Guidance for Controllers

Scope of the Article

This article does not deal with the Contingency planning aspects of ANSPs interruption of service, instead it refers to the tactical procedures of air traffic control service provision as a direct response to a system wide catastrophic event which compromises the safety and continuity of air travel.

System wide events in the context of the article include but are not limited to events related to volcanic eruptions, nuclear fallout, earthquakes, floods, acts of war and terrorism or any other catastrophic events which might render many airports and extensive airspace volumes unusable in wide geographic area for uncertain amount of time.

Tactical Management

The crisis management at ATC operations level (Tactical level) could be narrowed down to the following 3 phases:

Notification Phase

When an event of catastrophic nature, which renders certain airports and or airspace volume unusable, has been notified to ANSP, it is very important to evaluate the information, in particular to assess the origin of the information and gather as much detail as possible regarding the nature and the magnitude of the event. After the information has been assessed as being credible and safety critical, this initial information must be passed down to the individual ATC units, preferably with suggested courses of action for shift supervisors and controllers in the given circumstances.

Air traffic controllers without delay should notify all stations which are affected by the event.

Aircraft affected by the event might include but are not limited to:

  • inbound for destination within the area of crisis
  • having an alternate aerodrome within the area of crisis
  • planned their flight over the area of crisis
  • inbound for destination or having an alternate aerodrome in proximity to the affected area

A broadcast to ALL STATIONS might be necessary to share safety critical information. ATC units should be able to provide additional and more detailed information regarding the nature and the consequences of the event and the affected aerodromes/volumes of airspace as soon as further facts are available.

Information Collecting Phase

A crisis management team normally will be organised and engaged in a collaborative decision making process within the ANSP as per local instructions and national regulations. This team will monitor and manage the crisis, gather and distribute critical information and coordinate actions with the corresponding CAAs, military crisis command centers, the international intergovernmental organisations (such as EUROCONTROL NMOC, etc.) and adjacent flight information regions (FIRs).

At early stages of the event, airforce and military aircraft are likely to be deployed to participate in rescue operations from airbases located in proximity to the event.

In this phase, a course of actions and instructions should be elaborated that will enable ATC to mitigate the effects of the unplanned event. The course of actions will depend on the type of the event and the availability of resources, including but not limited to alternative aerodromes, suitable civilian and military airfields, and available airspace (as necessary military restricted areas will be assigned for civilian use in order to increase capacity).

It is important that the ATC units quickly ascertain the scale of the event and the implication for the safe ATC service provision. The ATC units must be able, without any delay, to pass information to the flight crews in order to facilitate their situational awareness and timely decision making. For example, such information may include (non-exhaustive list):

  • The nature, duration and consequences of the event
  • Availability of aerodromes and alternate destinations
  • Availability of airspace
  • Significant weather along the diversion route and over the alternate aerodromes
  • Impact on ATC service provided by ATC units affected by the event.

At this stage, flow control traffic restriction are likely to be put in place in order to limit both the traffic inbound to the affected area and also traffic in the adjacent areas which are very likely to be saturated, for a considerable time period, by diverging and/or holding flights .

Implementation Phase

In this phase the ANSP deploys its crisis management plan in close coordination with the adjacent FIRs and international organisations, as need may be.

The ANSP must be able to quickly assess the capacity of the ATC units to handle increased volume of traffic and process numerous re-routings and diversions to alternate aerodromes. In order to achieve this, the ANSP must be prepared to:

  • Open additional sectors
  • Provide extra staffing of controllers as necessary for short-term rotation in order to mitigate the controller’s overload
  • Examine any additional possibilities for re-routing and different alternate aerodromes usage as some aerodromes and airspace volumes might run out of capacity to handle non-planned traffic
  • Design an optimum plan for alternate aerodrome allocation taking into account all the information obtained from ground sources and from flight crews.

The different types of ATC units will face different operational challenges and no crisis management plan can predict for every eventuality. The ATC Units must be able, to the best of their ability, to respond in a safe and orderly manner with the system-wide crisis. Nevertheless the ATC Units must be prepared for certain common factors. Some of these expected common factors might include:

En-Route Control ATC Units The complexity and configuration of airspace could make the efficient and expedite provision of en-route control service problematic, particularly in congested areas of en-route airspace.


  • High volume of traffic
  • High complexity of operations due to non-standard traffic (diverging aircraft and re-routing actions) and missing/incorrect flight plans (due to possible strains on the FDP system related to the high traffic volume and numerous changes to flight trajectories)
  • Congested radio frequency due to clarifications requests and prolonged individual communications
  • Missed radio calls (due to increased discussion between the pilots and supernumerary crew and advisory messages on operator’s company frequencies)
  • Increased pilot workload
  • Increased coordination with adjacent ATC Units
  • Increased controller workload


  • Open additional sectors
  • Provide extra staffing to ensure frequent rotations on the positions and adequate rest periods
  • Provide additional advisory only frequency, as necessary, for the event clarification purposes
  • Advise crews on details regarding adjacent aerodromes including the weather conditions in case of capacity problems at the destination
  • Request information from crews about fuel reserve/flight endurance and runway parameters needed
  • Provide extra flight data and technical support personnel due to possible strain and overload of the existing CNS systems
  • Provide any other information pertinent to the situation awareness and to crews consideration related to decision making
  • Provide information for usable military airfields to aircraft which are likely to experience fuel shortage and coordinate deviations with the military controllers

Approach Control ATC Units

The proximity of the approach control unit to the affected area will determine, to a certain extent, the increase in controller's workload and may cause temporary disruption of the ATC service provided.


  • High volume of traffic (particularly in the terminal areas adjacent to the aerodromes and airspace volumes affected by the event)
  • Airspace capacity problems
  • Aerodrome capacity problems
  • Increased coordination with adjacent ATC Units
  • Flight crews not immediately familiar with aerodrome details and procedures
  • Increased pilot workload
  • Increased controller workload


  • Advise crews on details regarding adjacent aerodromes, including the weather conditions in case of capacity problems at the destination
  • Provide any other pertinent information to help pilots improve/maintain situation awareness and make informed decision about the continuation of the flight
  • Provide any additional information related to specifics of approach procedures and the aerodrome details to crews which are less likely to be familiar with the changed destination
  • Provide additional staffing to ensure frequent rotation and adequate rest of the controllers
  • Provide information for usable military airfields to aircraft which are likely to experience fuel shortage and coordinate the deviations with the military controllers

Tower Control ATC Units The proximity of the aerodrome to the affected area will determine, to a certain extent, the workload at the tower control unit.


  • Aerodrome capacity problems due to extra inbound traffic
  • Increased communication with crews requesting start up
  • Increased coordination with adjacent ATC Units
  • Crews not familiar with airport layout, slower taxi and poor situation awareness
  • Increased pilot workload
  • Increased controller workload


  • Delay or cancel start up clearances as necessary to keep number of flights in the affected area within the acceptable limits
  • Coordinate with ground control and airport authorities the usage of the available parking stands and consider possibilities to park aircraft on taxiways, if the capacity problem is severe
  • Broadcast Automatic Terminal Information Service (ATIS) messages informing crews of the event and the aerodrome procedures related to it in order to mitigate pilots' and the tower controllers' workload
  • Include in the ATIS messages information about closed airports within the affected area
  • Provide additional staffing to ensure frequent rotation and adequate rest of the controllers

Preparation - Organisational Aspects

It is well known that not all catastrophic events and related scenarios can be foreseen but a variety of measures might be taken in order to ensure institutional adequacy and personal training:

Organisational Awareness - training drills should include inter-organisational communication scenarios and should measure overall response time. The fast provision of additional ATCOs during emergency/crisis situations should be an objective at the administrative level. Periodic training and drills are likely to improve intra-organisational coordination.

Personnel Management - A non-routine situation may require additional staff to provide ATC service to non-affected traffic or act as liaison personnel. Training is another aspect that increases preparedness and reduces ATCO’s stress in non-standard situations.

Personal Awareness and Adequate Reaction – Controllers' awareness of any ongoing or planned disruption to the normal operations and communications within their area of interest should be maintained continuously. They should be prepared to provide any information necessary for the air crews to understand the scale of event and its related consequences for the safe conduct of the flights.

For further information on the organisational aspects of ANSP preparation at the strategic level for dealing with unexpected system wide events, see the dedicated article: System wide events - Guidance for ANSPs

Related Articles

Further Reading


  • Annex 11 – Air traffic services



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