GerardC:
HF data transmission works fine for RA (or pleasure boats email traffic).
At the moment (and in the near future), it is not used (or planned to be used) for commercial aviation.
Actually HACARS or HFDL (High Frequency Data Link) predates SATCOM ACARS and is still in use by a significant number of commercial airliners. I see a lot of traffic from HA, CO, AC, NW, NCA. UP, US, GTI, LH, ZS, AV, etc on everything from A319 to B777. One I don't see is AF, at least from my location.
My guess would be as SATCOM came out some carriers, manufacturers, etc may have moved to it and removed the HF capability, some may have both, and possibly some just have VHF and HF ACARS.
These initial ACARS systems have been extended to offer worldwide coverage, even in mid-ocean and
sparsely inhabited areas, using the Inmarsat facilities and HF data link, and to cover not only company
communications but also ATC services, starting with predeparture and oceanic clearances.
On aircraft delivered since 1998, the ACARS unit has been replaced by the Air Traffic Services Unit
(ATSU), which is designed to also accommodate safety-related ATC functions using the Aeronautical
Telecommunications Network (ATN), offering the majority of ATC and other communication services now
using voice, and more importantly, offering profitable migration to the ATN. The ATSU is the first unit to
host software from a number of different vendors. The same ATSU is also used on the A320 family of aircraft.
The ATN upgrade is being implemented to be available when the corresponding communication and
ATC services are in service.
From: New Avionics Systems —Airbus A330/A340
http://www.davi.ws/avionics/TheAvion...ook_Cap_30.pdf