IMS EMEA Newsletter Issue 1 - December 2009

Viable, versatile HF datalink

Vol1 5Once upon a time, high-frequency (HF) radio was a thing of wonder, the miracle technology that allowed Marconi to introduce practical trans-ocean wireless nearly a century ago. It reached its zenith in the 1950s, before the advent of satellite communications. But since then it's had a lot of bad press. Unreliable, cumbersome, labour-intensive – HF has had its day, say the critics.

Well, here's a message loud and clear for the critics. HF datalink (HFDL) for air transport is alive and well and has emerged as a real alternative to satcoms on many long-haul routes. Less well understood is its ability to stand in for VHF on short-haul and regional aircraft in areas where it's hard to make a business case for the necessary ground stations, as is often the case in the developing world and the further reaches of countries like Australia and Canada.

HFDL has been available to the airlines for just over a decade. In that time usage has grown by an average of 20 per cent a year. More than 60 airlines with 1,200 aircraft equipped send a million messages a month. Growing numbers of new aircraft are being built with HFDL available as an option, and more airlines than ever are specifying it.

Along with VHF and satcoms, HFDL is part of the GLOBALink portfolio of services that ARINC offers to support access to industry-standard ACARS air-to-ground data communications. The company was the first to offer HFDL service, and is still the only provider with global coverage - and that's one of the great strengths of this technology.

VHF datalink is very effective over line-of-sight ranges in continental airspace. But it's physically impossible to place the relay stations on the oceans or in wildernesses like the poles and Siberia. Geostationary satellite systems like Inmarsat provide round-the-world coverage but can't reach the poles. Iridium's low-Earth-orbit satellites overfly the poles but the system has yet to win broad air transport industry acceptance. Only HFDL can offer a combination of global coverage and a significant installed base.

The ARINC HFDL service owes its reach to a network of 15 ground stations embracing most of the Earth's surface – around 168 million square miles, including both poles – and with overlapping coverage zones to provide a high degree of service continuity in the event of a station outage. In fact so far this year the system has displayed 100 per cent availability – a reflection of ARINC's continued investment in the infrastructure and long-term commitment to making the service available.

With its over-the-horizon abilities depending on refraction from the notoriously variable ionosphere, HF radio has a past history of unreliability. If conditions weren't right, an airborne radio operator might try time and again and still not get through. Modern digital signal processing has changed all that.

Recent software innovations in the HFDL radios offered by avionics market leaders Honeywell and Collins mean that message success rates are comparable with those of the VHF and Inmarsat satellite datalink services. And when it comes to crew workload, the radios cope with varying propagation conditions by automatically scanning for and selecting the best frequency to use at any given time.

These flexible, intelligent airborne systems are supported by a ground network with plenty of capacity to accommodate future traffic growth and the resilience to cope with the natural hazards that can affect HF propagation.

The network design allows for up to four channels per ground station. At present 13 out of the 15 installations are using just two each, while the remaining two stations have three in operation. Traffic load is constantly monitored and additional capacity can be added as required.

As a technology HFDL is intrinsically less vulnerable than HF voice to disruption from solar storms. Because it needs less than half as much bandwidth, it can remain usable at times when HF voice won't work, as was the case during the Halloween solar storm of 2003.

These are some of the strengths that have made HFDL a standard medium for the support of long-haul operations all over the world. But there is also a compelling case for its use in short-haul and regional operations into areas where VHF datalink is not available. In exchange for a comparatively modest investment in HFDL equipment and service, the carriers could enjoy the cost savings and operational efficiencies already proved in the VHF domain.

All that's missing now is HFDL equipment optimised for the narrowbodies, regional jets and turboprops. And that will surely be forthcoming when the carriers signal their broad commitment to HFDL by, for instance, specifying datalink capability for the mandatory HF voice installations on new aircraft destined to fly oceanic routes.

Rumours of the decline of HF have been greatly exaggerated. HF datalink is delivering the goods every day on the intercontinental routes – now it's ready to fill the gaps in datalink coverage that affect the bottom lines of short-haul and regional carriers.



IMS EMEA Newsletters 


Vol1 6smallFinal Call

ARINC has just completed a project to install the AviaVox artificial voice system, an intelligent announcement system, into Manchester Airport's three terminals.

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