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In the context of STCA standardisation currently under progress in Europe, the I-AM-SAFE project evaluated the applicability and usefulness of the methodology used in the ACAS field in the prospect of establishing quantified performance requirements for STCA.
I-AM-SAFE stands for IAPA – ASARP Methodology for Safety net Assessment – Feasibility Evaluation. IAPA and ASARP are previous ACAS safety studies.
The project represented about a one man-year effort between June 2006 and March 2007. The work was performed by a consortium of two organisations Sofréavia and DSNA involved in ACAS standardisation and safety evaluation for more than a decade.
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This feasibility study built upon the experienced gained through the development of the ICAO performance SARPs for ACAS, and the methodology and tools that supported various ACAS safety and performance studies of the EUROCONTROL ACAS and Mode S Programme. These tools consist of a set of models that allow the replication of the environment in which ACAS is being operated in Europe, including the European ‘safety encounter model’ delivered by the ASARP project and the European ‘ATM encounter model’ delivered by the IAPA project.
For the I-AM-SAFE study purposes, a simplified STCA model has been implemented, which complies with the essential features of the reference STCA system defined by EUROCONTROL. This model was used to simulate STCA behaviour in encounters generated from the safety and ATM encounter models. Four sets of STCA configuration parameters were investigated during the study, which spanned the full range of parameter values recommended by EUROCONTROL. ACAS simulations were also performed to help assessing the relevance of the STCA alerts, identify missing alerts and provide elements on the STCA / ACAS interaction issue.
Because of the investigation nature of the project, the STCA performance metrics evaluated during the study were quite simple and did not yet consist of complex performance indicators. The focus was on the general trends that could be observed in terms of STCA alert occurrences, warning times and durations depending on the scenarios. An insight was also performed on the level of interaction with ACAS alerts.
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The study demonstrated the operational realism of the reference STCA model implemented during the project despite its simplicity. It also pointed out the potential interest of implementing other optional features described in the EUROCONTROL guidance material for STCA, as well as developing a surveillance model that would be representative of current surveillance performances in Europe.
The encounter model-based methodology has demonstrated to be applicable and useful to evaluate the performance of STCA, and the possible interaction issues with ACAS, although some adaptations would be required to specifically address STCA. In particular, the study results are in favour of the development of an ATC incident-based encounter model (derived from real incidents that occurred in Europe) that would encompass the interest of both the safety and ATM encounter models without their limitations.
Although quite simple, the STCA performance metrics evaluated during the study have shown the influence of the encounter characteristics (i.e. risk bearing situations or day-to-day conflicts in TMA or en-route), the STCA configuration (i.e. with or without the use of CFL) and parameters (i.e. high or low values), as well as the quality of the data provided to STCA, on the likelihood and relevance of the alerts. To allow evaluating the ability of STCA to alert the controller with sufficient warning time, the study results also pointed out the interest to model the controller intervention in response to an STCA alert apart from the encounter model itself.
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Conclusions and recommendations |
This feasibility study confirms that the STCA standardisation process can benefit from the experience gained in the ACAS field. Indeed, both systems raise similar issues to a certain extent. Further, the possible interaction between the two safety nets is an area of concern that needs particular attention.
Taking into account the main study findings, a more sophisticated framework that would enable the evaluation of STCA performance and safety benefits while taking into account the effect of ACAS operations has been proposed. This framework builds upon the encounter model-based methodology and the various areas of improvement identified during the study.
For maximum safety benefits, it is recommended that the standardisation of STCA be supported by a comprehensive evaluation of the effectiveness of STCA and its possible interaction with ACAS.
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I-AM-SAFE overview paper (465K) |
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A paper on the applicability and usefulness of the encounter model-based methodology for safety net assessment
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I-AM-SAFE Feasibility Study Report (375K) |
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The final report of this study.
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I-AM-SAFE replay material (17.7M) |
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A Microsoft PowerPoint presentation with linked video files showing the analysis of 9 typical encounters; the files in the Zip archive must be extracted into the same directory for the links to work. |
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Last validation: 04/04/2008
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