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 due to this phenomenon is a common occurrence and can lead to flight safety incidents.

The purpose of the call sign similarity service is to help aircraft operators (AOs) to de-conflict similar call signs embedded in their schedules. This helps to reduce the incidence of call sign confusion events and improves the safety of the Network.

The service is delivered by the Call Sign Management Cell (CSMC) which forms part of the Network Manager Operations Centre (NMOC).

Currently two levels of the service are available:

  • Service Level 0 - primarily raises awareness about CSS reduction processes,
  • Service Level 1 - provides support to de-conflict or eliminate similar call signs within a single aircraft operator's schedule with the help of the Call Sign Similarity Tool (CSST).

To drive the development of the CSS Service and its support tool (CSS Tool), a users group has been established. The target membership of this users group is: ANSPs, Airspace Users , Airports, Military Stakeholders as appropriate. IATA and ICAO Paris office are also observers to the CSS users Group.


  • de-conflicted call signs


Related links

Access conditions

Service Level 0 is public.

Service Level 1 is available upon subscription and signing of a service agreement and includes access to the CSS Tool.