eATM Portal

ATC02.9 — Short Term Conflict Alert (STCA) for TMAs

STCA (Short Term Conflict Alert) is a ground system designed and deployed to act as safety net against the risk of having collisions between aircraft during airborne phases of flight. STCA can be used in both en-route and TMA surveillance environments.

The difficulty of STCA development lies in the need to avoid having a high nuisance alert rate, while still making sure that real conflicts always trigger an appropriate and timely warning. Specific tuning is necessary for STCA to be effective in the TMA, in order to account for lower separation minima, as well as increased frequency of turns, climbs and descents.

It is therefore recognised that STCA may not be operationally usable in some dense TMA operations, because the nuisance alert rate generated by a linear STCA algorithm is evaluated to be too high.

The aim of this Objective twofold:
• To address the implementation of STCA functionality in TMAs
• For the TMA where, due to their complexity, the linear STCA algorithms are not fit for purpose, to address the improvement of the STCA functionality. This could be achieved by using multi-hypothesis algorithms, or other technical solutions ensuring earlier warning and lower nuisance alert rates related to steady and manoeuvring aircraft, in comparison to linear STCA algorithms.

NOTE 1: the scope of this Objective is limited to the deployment of the STCA functionality in TMAs. The (former) objective ATC02.2 which was addressing both en-route and TMA environments had its scope reduced to en-route allowing to consider it as achieved.

NOTE 2: SLoA ATC2.9-ASP02 does not have an associated FOC date and should be considered for specific local needs (refer to the description of SLoA below).

NOTE 3: : In certain more complex environments specific tuning is necessary for STCA to be effective especially in the terminal airspace in order to account for lower separation minima, as well as increased frequency of turns, climbs and descents. In these situations, the STCA may need to be improved with e.g. the use of multi-hypothesis algorithms, aiming to reduce the number of false and nuisance alerts compared to existing technologies, while maintaining the detection of genuine alerts (SLoA STCA02.9-ASP02). The improved STCA algorithms lead to more precise warnings and fewer false and nuisance alerts when compared against existing STCA technology.

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.

Air Navigation Service Provider


Related Elements

Applicability Area(s) and Timescales

Applicability Area:
All ECAC States except: Albania, Bosnia and Herzegovina, Cyprus, Maastricht UAC. Plus: Israel, Morocco
(Note: TMAs, according to local business needs)
Timescales From By Applicable to
Initial operational capability 01-01-2018 Applicability Area
Full operational capability 31-12-2020 Applicability Area

Links to SESAR Solutions

Links to PCP ATM Sub-Functionalities


Applicable legislation
Applicable ICAO Annexes and other references
Deployment Programme 2022
Operating Environments
Terminal Airspace

Expected Performance Benefits

Identification of conflicts between flights in TMAs. STCA based multi-hypothesis algorithm will provide an improved STCA (improved rate of genuine alert while maintaining the rate of nuisance alerts at an operationally acceptable level), thereby enhancing safety in TMAs. For TMAs with high trajectory uncertainty where operation of a single-hypothesis STCA would currently unacceptable due to its low performance, the introduction of multi-hypothesis algorithms will make it possible to implement STCA.
Operational efficiency
Cost efficiency
  Code Title From By Related Enablers
ASP01 Implement the STCA function in TMA
  • 01-01-2018
  • 31-12-2020
ASP02 Improve the STCA functionality
ASP03 Develop and implement ATC procedures related to the use of STCA in TMA
  • 01-01-2018
  • 31-12-2020
ASP04 Align ATCO training with the use of STCA in TMA
  • 01-01-2018
  • 31-12-2020
ASP05 Develop a local safety assessment
  • 01-01-2018
  • 31-12-2020
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

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


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

ASP01, ASP02, ASP03, ASP04, ASP05

EUROCONTROL - Safety Nets - A guide for ensuring effectiveness - August 2017

ASP01, ASP02, ASP03, ASP04, ASP05

SJU - SESAR Solution 60: Data Pack for enhanced STCA for TMA

ASP02, ASP03, ASP04, ASP05

Consultation & Approval

Working Arrangement in charge
Safety Team (SAFT)
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