ELSA Study and Recommendations

November 2016

Background to Datalink and ELSA

The availability, in Europe, of high quality data communications capabilities for ATM with appropriate Quality of Service is essential to reach the Single European Sky (SES) objectives and subsequently the deployment of SESAR.

The baseline for SESAR includes a data communications capability based on VDL/2 which is expected to support the initial SESAR developed datalink services including Initial 4D.

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SESAR and Datalink

Mandate 29/2009:

SES Data Link Services Implementing Rule (DLS IR)(EC Reg. 29/2009) specified European implementation of datalink.

Performance Issues:

Performance issues of VDL/2 raised concern on the usability of the system. Some issues attributed to specific avionics installations but other problems remained to be solved.

The problem became highly visible and lead to a European Commission workshop in September 2013

EASA Report: April 2014

EASA conducted an investigation, under the mandate of the EC, into the performance issues of VDL/2 and published their report. The report identified a 10-point Action Plan which the SJU was asked to progress.

EC request to SESAR: June 2014

The EC wrote to the SJU requesting R&D actions on the points raised in the EASA report.

SJU Admin Board: June 2014

The SJU Admin Board gave the go ahead for the launch of an additional call to support the required actions on VDL/2.

Call Published : August 2014

VDL Mode 2 Measurement, Analysis And Simulation Campaign

Call award and Execution : Feb 2015-Jun 2016

ELSA Consortium delivered the Final Report and all supporting technical material in June 2016. SJU published the documents in June 2016.

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Sequence of Events

Provider Abort occurrences could be attributed to a combination of the following factors:

(*)

• Use of a single frequency for Common Signalling Channel (CSC) and data.

• Concurrency of AOC and ATN traffics over this single frequency channel, leading to an

excessive channel usage level compared to the ATN protocol needs.

• The VGS networks are mainly driven by AOC needs, leading to a saturated and non-optimised

VGS network for en-route (over FL 285) purposes.

• The resulting RF complex environment (where there are many VGSs in view) introduces some

unexpected demands on the VGS handover logic at airborne level.

• Increase of the Radio Frequency congestion leading to delays in data transmissions or

disconnections.

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Single frequency is not the only cause!

Statement in the EASA report

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ELSA Objectives

• Collection and analysis of data from avionics and ground-systems to identify the issues affecting the end-to-end performance of the VDL2 Datalink;

• Modelling and analysis of the options for multi-frequency VDL2 deployment, in particular the options for channel use, frequency assignment, network topology and network management;

• VDL2 protocol optimisation in support of both ATN and AOC communications (through RF Level Modelling and Testing)

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VDL2 Measurement Analysis and Simulation Campaign (ELSA Study)

Unique Consortium

Outstanding Work

On Time Delivery and Sharing

Concrete and Actionable Recommendations

More than 400 revenue and measurement flights

3 million air/ground exchanges, 700 hours of simulation

350,000 flight hours, and stress testing of common avionics

100s of protocol optimisations

More than 1000 pages of technical reports

16 months project

ELSA Study and Recommendations

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A Unique Consortium & Partnership

More than 400 revenue and measurement flights

3 million air/ground exchanges, 700 hours of simulation

350,000 flight hours, and stress testing of common avionics 100s of protocol

optimisations options

More than 30 MF deployment options

Network Optimisation

More than 1000 pages of technical

reports

A very committed team !

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ELSA WBS Mapping Project Objectives

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Where Does the Problem Come From?

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Extensive Flight Campaign

(*) Complemented by specific RF tests

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Hidden Transmitter Causing Disconnection

After Saturation, hidden transmitters effect is the main contributor to the RF issues encountered.

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Hidden Transmitter Causing Disconnection

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Best in Class Performance

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A Rigourous Process for MF Selection

Phase 1

Phase 2

Phase 4

Phase 3 (Validation)

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MF Solution and Transition Roadmap

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Protocol Optimisation and Stress Testing

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Both congestion and lack of coverage

PA is also due to a lack of coverage

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Protocol Optimisation Opportunities

The D11 is the main ELSA deliverable

D08,D09 and D10 are supporting technical documents

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The links between deliverables

D08

D09

D10

D11

WA1 Conclusions

WA2 Conclusions

WA3 Conclusions

- Bring the big picture - Consolidate the inputs - Develop the Recommendations - Cluster recommendations

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Clear and Actionable Recommendations

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Ground Recommendations • Improve the VHF Ground Station (VGS) network and fix

the ground system issues – Use a dedicated channel for transmissions at the airport in regions with high en-route traffic

levels.

– Progressively implement additional VDL2 frequencies in accordance with the traffic level.

– Optimise the en-route VGS network coverage.

– Use the CSC as common control channel only, unless traffic level is very low.

– Implement ELSA recommended protocol optimisation (limit AVLC frame size)

– Ensure the availability of a fifth VDL2 frequency (at a minimum).

– Favour alternative communications means for AOC, with a priority to the airport domain.

– Fix the ELSA identified ground system problems (unbounded retry, Clear Request, Disconnect Mode)

• Start implementing the transition roadmap to the MF VDL2 target technical solution

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Avionics • Harmonise avionics’ performance, especially MF

capability:

– Upgrade of avionics to the “best in class” performance, showing no operational issues in the extensive validation performed by ELSA, and

– supporting MF operations, especially FSL-based, GRAIHO and

Autotune handovers.

• Update flight crew operational procedures to avoid unnecessary avionics resets.

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Standardisation and Compliance • Define and implement an effective datalink end-to-end system

certification process and reference material for the ground network infrastructure (MOPS-like).

• Include the selected interoperability improvements and clarifications in the relevant standards, and implement the resulting changes: – Handover algorithms:

– Detect peer loss of communication:

– Reduce ground ACARS latency (check/link with T2 AVLC).

– Non-use of IDRP – progressively remove the IDRP usage on the airborne side.

– Concatenate the CPDLC LACK (DTPDU) and the TP4 ACK in the same CLNP message.

• Include updates for MF interoperability (as identified in ELSA interoperability tests) in the relevant standards.

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Network Implementation and Oversight Framework

For coordinated deployment and operation: • Establish/empower a pan-European air/ground datalink

implementing function having appropriate steering responsibilities.

• Establish/empower a pan-European ATN/VDL2 performance monitoring and spectrum coordination function.

• Establish/empower a pan-European ATN/VDL2 end-to-end certification and oversight function for validating (ground and airborne) sub-systems acceptability.

The recommendations proposed for implementation will provide, if addressed in a coordinated way by all stakeholders, sufficient ATN/VDL2 capacity to support the deployment of ATS data link services.

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Conclusion