---
title: "CNS.TR.205 Allocation and use of Mode S interrogator codes — SPECIFIC REQUIREMENTS FOR PROVIDERS OF COMMUNICATION, NAVIGATION, OR SURVEILLANCE SERVICES, ATM/ANS · Avioverse"
description: "A surveillance services provider shall only operate an eligible Mode S interrogator, using an eligible interrogator code (IC), if it has received an…"
url: "https://avioverse.aero/regulations/easa/atm-ans/part-cns/subpart-b/cns-tr-205"
---

# CNS.TR.205 Allocation and use of Mode S interrogator codes

SPECIFIC REQUIREMENTS FOR PROVIDERS OF COMMUNICATION, NAVIGATION, OR SURVEILLANCE SERVICES · Regulation (EU) 2017/373 · EAR revision 12 Mar 2025

IR Implementing rule

## CNS.TR.205 Allocation and use of Mode S interrogator codes

(a) A surveillance services provider shall only operate an [eligible Mode S interrogator](https://avioverse.aero/glossary/easa/eligible-mode-s-interrogator), using an eligible interrogator code (IC), if it has received an interrogator code allocation, for this purpose, from the Member State concerned.

(b) A surveillance services provider that intends to operate, or operates, an eligible Mode S interrogator for which no interrogator code allocation has been received, shall submit to the Member State concerned an interrogator code application, include the following key items, as a minimum:

(1) a unique application reference from the Member State concerned;

(2) full contact details of the Member State’s representative responsible for the coordination of the [Mode S interrogator](https://avioverse.aero/glossary/easa/mode-s-interrogator) code allocation;

(3) full contact details of the [Mode S operator](https://avioverse.aero/glossary/easa/mode-s-operator)’s point of contact for Mode S IC allocation matters;

(4) Mode S interrogator name;

(5) Mode S interrogator use (operational or test);

(6) Mode S interrogator location;

(7) Mode S interrogator planned date of first Mode S transmission;

(8) requested Mode S coverage;

(9) specific operational requirements;

(10) SI code capability;

(11) “II/SI code operation” capability;

(12) coverage map capability.

(c) A surveillance services provider shall comply with the key items of the interrogator code allocations it has received, including the following items as a minimum:

(1) the corresponding application reference from the Member State concerned;

(2) a unique allocation reference from the interrogator code allocation service;

(3) superseded allocation references, as required;

(4) allocated interrogator code;

(5) surveillance and lockout coverage restrictions under the form of sectored ranges or Mode S coverage map;

(6) implementation period during which the allocation needs to be registered into the Mode S interrogator identified in the application;

(7) implementation sequence which needs to be complied with;

(8) optionally and associated with other alternatives: cluster recommendation;

(9) specific operational restrictions, as required.

(d) A surveillance services provider shall inform the Member State concerned at least every 6 months of any change in the installation planning or in the operational status of the eligible Mode S interrogators regarding any of the interrogator code allocation key items listed in point (c).

(e) The surveillance services provider shall ensure that each of their Mode S interrogators uses exclusively its allocated interrogator code.

IR · CNS.TR.205 — Regulation (EU) 2017/373 · Regulation (EU) 2023/1771 · ATM/ANS Easy Access Rules · EAR revision 12 Mar 2025

[All rules in SUBPART B — TECHNICAL REQUIREMENTS FOR PROVIDERS OF COMMUNICATION, NAVIGATION OR SURVEILLANCE SERVICES (CNS.TR)](https://avioverse.aero/regulations/easa/atm-ans/part-cns/subpart-b)

Consolidated from the EASA Easy Access Rules (revision 12 Mar 2025, extracted 13 Oct 2026) for convenience. Not the official publication — verify against the Official Journal of the European Union and the EASA publications before operational use.