Clearance - No clearance - we take the deviation we need - The information on the weathear deviations will be broadcasted or/and monitored directly on VHF 123.45 that everybody should syntonize ... unless I'm wrong and the appropriate frequency is different in that area (?)
You are right, we
ALL take whatever weather deviation is needed,
AND (preferably before deviating...) we send a message (HF or CPDLC) : "
request deviation up to XX Nm due to weather".
Do not forget these routes are not as crowded as the NAT OTS area : after dozens of SA crossings (before and after AF 447 crash), I can't remember of much (if any) "
deviation" chat on 123,45 (or 121,5).
Concerning the questions about ACARS transmissions, sorry, I fail to understand the point : as long as the system is in VHF range, ACARS goes through VHF (as it is much cheaper). When out of VHF range (or if no VHF network exists), the system switches automatically to SATCOM without any crew action.
You get F/D alert messages :
- in VHF range, if you move VHF frequency out of the "DATA" position ;
- out of VHF range, if satcom is lost.
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.