Europe starts to use Mode S Surveillance Identifier (SI) Interrogator Codes

Brussels, Belgium – EUROCONTROL, the European Organisation for the Safety of Air Navigation, has started allocating a new type of Mode S Interrogator Code (IC) to cope with the expansion of Secondary Surveillance Radar Mode S (SSR Mode S) systems in Europe.  Mode S systems have been introduced in Europe in order to improve air traffic management (ATM) surveillance and enhance current SSR surveillance. Mode S enhances the quality, detection, identification and altitude reporting of aircraft within the airspace. Each SSR Mode S sensor or cluster of sensors requires an Interrogator Code, either an Interrogator Identifier (II) or a Surveillance Identifier (SI), in order to selectively interrogate aircraft. The codes are allocated by the EUROCONTROL Mode S IC Allocation Cell.

Assignment of interrogation codes is carefully managed to ensure that identical codes are not used in overlapping Mode S coverage areas. The Mode S IC Allocation Cell has succeeded in allocating II codes to more than 120 Mode S radars since the first installations in 2002. However, there are only 15 unique II codes, and demand now exceeds supply. This has resulted in coverage restrictions being imposed on newly installed Mode interrogators.

In order to enable the deployment of SSR Mode S radars to continue, and coverage restrictions to be limited or even lifted, EUROCONTROL has started allocating a new Interrogator Code, called a Surveillance Identifier (SI) code. There are 63 SI codes, and the first of these have been allocated to Mode S radar installations in France and the Netherlands, resulting in extended Mode S surveillance coverage.

 “The allocation of an SI code to the Schiphol Mode S radar enables the LVNL to fulfil the operational requirements by deploying the Mode S TMA radar without coverage restrictions until 150 Nm”, said Ron van Scheppingen from the LVNL - Air Traffic Control of the Netherlands.

The use of SI codes was made possible by the mandatory carriage of SI capable Mode S transponders promulgated in the frame of the EUROCONTROL Mode S Programme, and will be further supported by the Single European Sky (SES) regulation developed in collaboration with the European Commission.

EUROCONTROL manages the European-wide coordinated allocation of Mode S Interrogator Codes on behalf of ICAO for the EUR Region, in close cooperation with national regulatory authorities, air navigation service providers and radar manufacturers.

Further information on the Mode S IC Allocation and related regulations can be found on the EURONTROL website:
for the Mode S IC Allocation coordination activity
for the implementing rule for Interoperability on Mode S IC allocation, requiring SI code support from radars
for the implementing rule for Interoperability on Surveillance performance and interoperability requirements, requiring SI code support from transponders


For further information about EUROCONTROL, click here

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