ATN 2002

1. ATN 2002 Industry Choice of Data Links Philip Clinch - SITA

2. Why so many data links ? • Airlines has been using ACARS data link for 20 years via VHF radio and for 10 years via satellite so they need the ACARS capability to be maintained through any modernization. • Air Traffic Service providers started designing Mode S data link 30 years ago but they only started using data link 10 years ago when they connected ATIS, Clearance and FANS systems to the ACARS networks. • ATN routing definition required aircraft to ground links transporting data in binary format and these were defined in the ICAO standards for AMSS (Satcom), VDL Mode 2 and HFDL. • The FAA desire to increase the number of voice channels in the VHF band capacity led to the definition of a system called VDL Mode 3 that provides data link integrated with digital voice. • The concept of ADS broadcast led to the definition of data links that provide aircraft to aircraft links using Mode S, UAT and VDL Mode 4. • Generic mobile communications systems including Inmarsat 64 kbit service and airport wireless LAN’s with megabit capacity have been adapted to provide “broadband” data links to aircraft.

3. Data Link Objectives • Data Links aim to serve the following cockpit applications that provide independent value and should not need to compete with each other for resources: • Aircraft Operational Communications (AOC) provided by ACARS that facilitate the efficient operation of the aircraft and monitor the status of the aircraft engines and other systems. • Controller Pilot Data Link Communications (CPDLC) and Automatic Dependent Surveillance (Contract) have shown in FANS-1/A they can take over routine exchanges from voice and allow increases in airspace capacity but they need better links in dense airspace. • ADS-Broadcast (augmented with TIS-B) is designed to show pilots the position of surrounding aircraft so that they can make better decisions about their route. • Electronic Flight Bags providing Aeronautical Information Services and Flight Information Services in digital format with updates in flight via the Inmarsat 64 kbit service and at airports via wireless LAN’s or 3G mobile networks.

4. Data Link Selection Criteria • Implementation feasibility • Provision of an implementation path that minimizes the initial cost and the impact on any existing systems to minimize the probability of delays undermining the cost/benefit assumptions. • Radio Spectrum availability • Limitation of requirement for spectrum for initial implementation and of effect on existing spectrum users, especially if the system needs the limited spectrum reserved for aeronautical use. • Cost/Benefit viability • Ability to deliver a net benefit after a predictable period by clearly solving an identified problem while limiting the avionics cost and using commercial technology that does not generate “hidden” costs from research subsidies.

5. Evaluation: VDL Mode 2 • Implementation feasibility: • Implemented in existing “Communications Management Unit” so requires no change to the airborne architecture. • System is being used today for ACARS communications so there is no technology risk that could undermine the benefits. • Radio Spectrum Availability • VDL Mode 2 is being implemented using one 25 kHz channel and one guard channel so it requires no major change to the band. • Cost/benefit viability: • Provides performance needed for CPDLC to take over routine exchanges that are saturating ATC voice channels. • VDL Mode 2 ground station development has been financed by the ACARS service providers without subsidies.

6. Evaluation: VDL Mode 3 • Implementation feasibility: • Replaces VHF analog radios with digital radios multiplexing 3 or 4 voice/data circuits per channel so gaining operational acceptance from pilots and Air Traffic Controllers could take a long time. • Radio Spectrum availability: • Aims to provide extra capacity in the VHF band where all channels have been assigned so it imposes complete reorganization. • Cost/benefit viability: • If deployed for voice VDL Mode 3 could enable CPDLC to take over urgent exchanges but it is not the ideal solution for data link. • Requires all aircraft to have digital radios and competes to increase voice capacity with VHF analog radios using 8.33 kHz channels that have already been installed in many air transport aircraft. • FAA is paying for prototype development and targets operation in 2008 (data in 2011) but VDL Mode 3 was designed in early 1990’s so it could be obsolete before deployment is complete.

7. Evaluation: Mode S Squitter • Implementation feasibility: • The ACAS/Mode S avionics vendors have developed the capability to send the aircraft position in the Squitter to support ADS-B. • Ground stations have been developed that relay Squitter data to surveillance processors and can broadcast TIS data. • Radio Spectrum Availability • Uses existing Mode S/ACAS channel and ADS-B should allow optimization of the transmission frequency. • Cost/Benefit viability • ADS-B use of a transponder mandated for all air transport aircraft has an advantage because it cannot work effectively if aircraft in the same airspace use different links. • Mode S Squitter usage enables an incremental implementation that minimizes the investment needed to achieve ADS-B benefits.

8. Evaluation: VDL Mode 4 • Implementation Feasibility • CAA Sweden prototype demonstrating ADS-B was developed into a trial system but the avionics do not fit into the data link architecture on air transport aircraft so it will be hard to gain adoption. • Radio Spectrum Availability • ADS-B support rules out use of a communications band so VDL Mode 4 would need to use the VOR band. • ADS-B use of a radio band vulnerable to interference from pirate transmitters limits its usefulness. • Cost/Benefit viability • VDL Mode 4 development has been covered by subsidies so the business case viability is questionable compared to VDL Mode 2. • Support on the same link for ADS-B and CPDLC is unique but this will make the system safety critical and more expensive than using the Mode S Squitter for ADS-B and VDL Mode 2 for CPDLC.

9. Evaluation: Inmarsat Swift64 • Implementation feasibility • Adaptation to aircraft use of existing Inmarsat 64 kbit/sec service used by mobile terminals such as videophones. • Additional avionics box has been developed that connects to the existing antenna used for classic Inmarsat aeronautical service. • Radio Spectrum availability • Aircraft shares spectrum with other Inmarsat 64K users making the allocation more economically viable. • Cost/Benefit viability • Minimum cost to get airborne 64 kbit/sec service needed for aircraft file servers that will offer user friendly applications like internet terminals on the ground. • Data cost per kilobit will be lower than via VHF links that require heavy ground network investment.

10. Evaluation: Wireless LAN/Mobile • Implementation feasibility • Adaptation to aircraft use of generic communications used for PC’s and mobile devices. • Aircraft on the ground at airports can use terminals developed for ground vehicles and will need only small antennae. • Radio Spectrum availability • Aircraft on the ground can use generic mobile spectrum but have to share with other users. Systems do not provide the range needed for airborne and that would require ITU coordination. • Cost/Benefit viability • Minimum cost broadband links to update data bases in aircraft file servers that use satellite links in flight. • Wireless LAN deployment could be costly but for applications that generate large data transfers the cost per kilobit will be low.

11. Data Link network financing • Aircraft data link networks can be financed by specific charges or treated as CNS infrastructure to be paid from general ATC charges which can create unfair competition. • Network service providers financed the ACARS VHF networks and the Inmarsat aeronautical service and have financed development of VDL Mode 2 ground stations and Inmarsat 64 kbit service. • ADS-B development using Mode S Squitter has been subsidized by the FAA but this service will be dedicated to aircraft safety and uses existing avionics so it minimizes the cost to the airlines. • VDL Mode 4 development has been subsidized by the EU which makes for unfair competition with commercially funded VDL Mode 2 services and its use would generate significant avionics costs. • Network service providers are taking the risk that the service benefits will convince airlines to install avionics to use the service and should not have to face subsidized competition.

12. Conclusion • Data Link selection depends on a mixture of factors but new systems should comply with the following criteria: • Allow incremental implementation • Maximize use of existing components • Avoid requirement for radio spectrum reorganization • Provide benefits without requiring fleet wide equipage • Support legacy applications • Offer sufficient benefits to avoid the need for subsidies • Airlines face extreme financial difficulties and cannot afford to have their money spent on technology that does not comply with these criteria. • SITA has invested in VDL Mode 2 ground stations and Inmarsat Swift64 because they comply with these criteria and offer the airlines a reliable way to obtain predictable benefits.