The Rockwell Collins ARINC ACARS® 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.
Typically the system has 100 per cent availability – a reflection of ARINC’s continued investment in the infrastructure and long-term commitment to making the service available.
In the past, with its over-the-horizon abilities depending on refraction from the notoriously variable ionosphere, old HF radio has reputation 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 such as Rockwell Collins means that message success rates are comparable with those of the VHF and 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 12 out of the 15 installations are using just two each, while the remaining three 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 notorious Halloween solar storm of 2003.
For further technical detail please see our "Downloads" section for our HFDL Overview Presentation