Call sign similarity tool

We help to de-conflict or eliminate similar call signs within a single aircraft operator’s (AOs) schedule prior to the start of the summer and winter season.

Log in Access conditions
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The use of similar call signs by aircraft operating in the same area, on the same radio frequency is referred to as 'call sign similarity.' The danger of an aircraft taking and acting on a clearance intended for another aircraft can lead to flight safety incidents.

The call sign similarity tool (CSST) allows aircraft operators to detect and then de-conflict similar call signs (according to a set of agreed rules) embedded within their aircraft operator schedules. This helps to reduce the incidence of call sign confusion events and improves the safety of the network.


The tool has comprehensive detection and de-confliction functionalities based on aircraft ‘city pair’ and airspace volume data stored by the Network Manager.

A stepped approach is being taken to organise access to the tool:

The Network Manager has put in place a 'service level 0' to provide the aircraft operators with the similarity rules to be applied in the process of the detection and resolution of conflicts.

  • Service level 1 operations focus on the detection and deconfliction of call sign similarities with a single aircraft operator’s schedule using the CSS tool.
  • If Service level 1 is successful, service level 2 will provide de-confliction between multiple aircraft operator schedules.
  • Service level 0 is public whereas service level 1 and 2 are available upon subscription and signing of a service agreement, and allow access to the CSS Tool.

EUROCONTROL established procedures with participating aircraft operators to monitor the CSST’s operational effectiveness. In particular, we are monitoring the anticipated improvements in safety performance in conjunction with the EUROCONTROL voluntary ATM incident reporting (EVAIR) scheme.

EVAIR records show that for those aircraft operators who use the CSST to de-conflict their own schedules there have been very few, if any, reported similarity and confusion events. Comparisons with their pre-CSST performance demonstrate that the CSST definitely helps reduce operational risk and improves flight safety.

Find out more

What is call sign confusion? Watch the video to learn more.

Access conditions

The tool is available to all aircraft operators through the Network Operations (NOP) portal. If you are a new user and do not have access to the protected NOP, visit our dedicated page to learn how to register.

Requesting access

Kindly submit an access request in order to obtain access to this tool. When filling out the form, please type in 'CSS tool' in the 'optional information' box to facilitate the handling of the request. Be sure to clarify that you intend to use the NOP to access the CSST.

Service request form