AF445 -No ACARS
AF 445 GIG-CDG hit some severe turbulence, the crew was unable to obtain descent clearance and applied oceanic procedures by transmissting MAYDAY to perform a level change.
Clearance to a new level was later granted by ATC.
There were no ACARS messages.
As to AF447 not sending a MAYDAY, just think how the events might have unfolded.
Pilots are in their seats in cruise, they may not be wearing their headset.
All the alarms go off and one is handflying in turbulence during the night with limited informations, as they both try to solve their problem.
To make a transmission, one has either to put on the headset and use it's mike or to use the handmike wich is hanging on its hook under the side window , that's if it's still there in the turbulence or upset.