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STCA System Outline Safety Case

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Category: Hazard Identification Documents Hazard Identification Documents
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Document title: Outline Safety Case for STCA System

Short Term Conflict Alert (STCA) is a ground-based safety net intended to assist the controller in preventing collision between aircraft by generating, in a timely manner, an alert of a potential or actual infringement of separation minima.

The European Convergence and Implementation Plan (ECIP) contains a pan-European Objective (ATC02.2) for ECAC-wide standardisation of STCA in accordance with the EUROCONTROL Specification for Short Term Conflict Alert. The document specifies, in qualitative terms, the common performance characteristics of STCA as well as the prerequisites for achieving these performance characteristics.

STCA System Block Diagram

STCA is not a new concept; it has been used operationally for many years. However, a survey of carried out by EUROCONTROL in 2004 by the European Safety Programme (ESP) Activity Field 4 revealed that most existing STCA implementations are inherently capable of functioning as efficient safety nets but that the existing capabilities are not always used effectively. The survey identified 14 areas of concern affecting all aspects of STCA operation. This led to the establishment of the Safety nets: Planning Implementation and eNhancements (SPIN) Task Force in 2005 to develop standards and supporting guidance material for safety nets, including STCA. The work involved 11 ATS providers, 5 industrial suppliers and the EUROCONTROL Agency in the development of the material.

STCA System Architecture

The STCA Specification developed by the SPIN Task Force includes the Concept of Operation and the key (minimum) functionality and performance parameters for STCA.

The key factors necessary for safe and effective use of the Concept are addressed and significant amongst these from a safety point of view are:

  • STCA policy, whereby the sole purpose (of STCA) is to enhance safety and its presence is ignored when calculating sector capacity. This means that the Controller is not to rely on it for maintaining safe separation, and so it is safe by definition in that regard.
  • The Conops is designed to ensure that urgent alerts are notified immediately, with a warning time of up to 2 minutes, and that nuisance alerts are minimised.
  • The requirements for training and awareness of controllers in the operation of STCA.
  • The importance of monitoring the performance of the system and optimising it to maintain effectiveness.
STCA Design Outline


This Outline Safety Case contains details of the safety assurance necessary to show that STCA will be acceptably safe in ATM operations. The arguments and the evidence to give this assurance are presented in the document. Only the assurance derived during system definition phase of the STCA lifecycle is covered in any detail. The Concept of Operations (Conops) upon which this Outline Safety Case is based was developed by the SPIN Task Force. The Conops is included in the EUROCONTROL Specification for Short Term Conflict Alert.

The purpose of the Outline Safety Case for STCA is to provide guidance material for ANSPs to assure their own implementations of STCA in accordance with the EUROCONTROL Specification. It addresses in detail the assurance and evidence from the System Definition stage within the Safety Assessment Methodology (SAM) lifecycle. It outlines the likely assurance and evidence for the later stages.

Individual ANSPs implementing STCA might be starting from different points, and their concept of operations, requirements and designs may differ. Guidance is provided throughout this document where individual ANSPs may need to deviate from, or augment the arguments and evidence in this Outline Safety Case.

If ANSPs adopt a lifecycle different to one in SAM, they will need to revise this Outline Safety Case.

Top Level Claim

The top-level argument for which assurance is required is that STCA will be acceptably safe in ATM operations.

General Assumptions

No general assumptions are made though ANSPs are reminded to include in their safety case any assumptions on which the top level argument is dependent e.g. the host surveillance system is acceptably safe

Associated Hazards

None on SKYbrary

Related Regulations and Standards

  1. EUROCONTROL Specification for Short Term Conflict Alert
  2. SRC Action paper SRC28/06. SRC Policy on Ground Based Safety Nets
  3. EUROCONTROL ESARR 4 Risk Assessment and Mitigation in ATM, Edition 1.0

Document Source

  • [{{{DocumentSourceURL}}} EUROCONTROL Guidance Material for Short Term Conflict Alert Appendix B-3 Outline Safety Case for STCA System]</protect>