Traditional Mode A/C Secondary Surveillance Radar stations continuously interrogate all aircraft within their range. Mode S Secondary Surveillance Radar stations establish individually addressed interrogations with aircraft within their coverage.
In order to avoid ambiguity in operating the system, it is essential that each Mode S radar be allocated an Interrogator Code (IC) which, in a coordinated operational environment, protects its operation from interference with other Mode S radars operating in overlapping or contiguous airspace.
As the number of Interrogator Codes is limited, a centralised IC allocation system has been established for an optimised coordinated approach to the allocation and implementation of the ICs used by Mode S radars.
In the ICAO European region, the centralised IC allocation system is managed by EUROCONTROL Network Manager’s SCC Unit on behalf of ICAO’s EUR regional office. We also support ICAO’s Middle East regional office in Mode S IC Allocation coordination for the ICAO Middle East Region. Interrogator code allocation requests for this region have to be submitted through the MID ICAO regional office. The stakeholder working groups covering this activity are the Network Surveillance User Group (NSUR) and the Mode S Interrogator Code Coordination Group (MICOG).