eATM Portal

ATC20 — Enhanced STCA with down-linked parameters via Mode S EHS

STCA (Short Term Conflict Alert) is a ground system designed and deployed as last Safety Net against the risk of collisions between aircraft due to separation loss. Enhanced STCA can be used both in En-Route and TMA radar environments to improve prediction of potential conflicts and reduce false alert rate. The difficulty of STCA development lies with the need to avoid a high false alert rate versus the need of ensure that all risk of collision always triggers a timely warning.

This objective addresses the enhancement of the STCA safety net with selected flight level (SFL) information down-linked from the suitably equipped aircraft via the Mode-S EHS protocol. Enhancing the STCA with the information downlinked from the aircraft will improve the warning times, decrease the rate of nuisance alerts and maintain or improve the rate of genuine alerts.

NOTE: The implementation of this functionality requires the appropriate equipment on board. The airborne carriage and operation of Mode S EHS capable transponders is addressed by objective ITY-SPI (ITY-SPI-USE06 and ITY-SPI-MIL02) based on the provision of Regulation (EU) No 2020587/386.

NOTE FOR MILITARY AUTHORITIES: It is the responsibility of each military authority to review this Objective IN ITS ENTIRETY and address each of the SLoAs that the military authority considers RELEVANT for itself. This has to be done on top and above of the review of "MIL" SLoAs which identify actions EXCLUSIVE to military authorities.

Regulator / Air Navigation Service Provider


Related Elements

Applicability Area(s) and Timescales

Applicability Area:
All EU SES States except: Bulgaria, Estonia, Latvia, Malta, Slovak Republic. Plus: Albania, Israel, Moldova, Montenegro, Serbia, Türkiye, United Kingdom
(ACCs and collocated ACCs/APPs. Stand-alone APP Units providing services to more than 100K IFR movements per year. Subject to local need.)
Timescales From By Applicable to
FOC used for Analytics functioning only - not for implementation planning 31-05-2019 Applicability Area
FOC used for Analytics functioning only - not for implementation planning 01-01-2030 Applicability Area

Links to SESAR Solutions

Links to PCP ATM Sub-Functionalities

ICAO Block Modules: No associated data


Applicable legislation
Regulation (EU) No 2020/587 amending Regulation (EU) No 1207/2011 (SPI)
Applicable ICAO Annexes and other references
Deployment Programme 2022
Operating Environments
Terminal Airspace

Expected Performance Benefits

A comparative analysis of STCA enhanced with the SFL DAP against conventional STCA showed that the use of the SFL DAP improves warning times, decreases the rate of nuisance alerts and maintains or increases the rate of genuine alerts.
Operational efficiency
Cost efficiency
  Code Title From By Related Enablers
REG01 Mandate the airborne carriage and operation of suitable equipment (Mode S EHS transponders)
  • 31-05-2019
  • 01-01-2030
ASP01 Deploy enhanced STCA function with the use of Selected Flight Level downlinked parameter
  • 31-05-2019
  • 01-01-2030
ASP02 Develop and implement ATC procedures related to the availability for display and use of SFL in the STCA functionality
  • 31-05-2019
  • 01-01-2030
ASP03 Align ATCO training to address the availability and use of the SFL downlinked parameter
  • 31-05-2019
  • 01-01-2030
ASP04 Develop a local safety assessment
  • 31-05-2019
  • 01-01-2030
Code Dates
1999 99
2000 00
2001 01
2002 02
2003 03
2004 04
2005 05
2006 06
2007 07
2008 08
2009 09
2010 10
2011 11
2012 12
2013 13
2014 14
2015 15
2016 16
2017 17
2018 18
2019 19
2020 20
2021 21
2022 22
2023 23
2024 24
2025 25

Supporting Material

Title Related SLoAs

EASA - CS ACNS - Certification Specifications for Airborne Communications Navigation and Surveillance - Issue 3 / 05/2021


EUROCAE - ED-73F - Minimum Operational Performance Specification for Secondary Surveillance Radar Mode S Transponders 12/2020


EUROCONTROL - Air Navigation Systems Safety Assessment Methodology (SAM) - Version 2.1 / 11/2006


EUROCONTROL - EAM 4 - ESARR 4 - Risk Assessment and Mitigation in ATM - Edition 1.0 / 04/2001


EUROCONTROL - GUID-159 - EUROCONTROL Guidelines for Short Term Conflict Alert - Part I to III - Edition 1.0 / 01/2017


EUROCONTROL - SPEC-108 - EUROCONTROL Specification for Short Term Conflict Alert - Edition 1.0 / 11/2007

ASP01, ASP02, ASP03, ASP04

ICAO - Doc 9871 - Technical Provisions for Mode S Services and Extended Squitter - Advanced Edition / 04/2012


SJU - SESAR Solution 69: Data Pack for Enhanced STCA with down-linked parameters

ASP01, ASP02, ASP03, ASP04

Consultation & Approval

Working Arrangement in charge
Outline description approved in
Latest objective review at expert level
Commitment Decision Body
Provisional Council (PC)
Objective approved/endorsed in
Latest change to objective approved/endorsed in