Role of ACARS event log:
"Event Log – In near real-time, the event log gives you a view of what is happening
in your fleet worldwide. From data taken from the Aircraft Management System and
transmitted through the EFB channel, you can determine what aircraft are on, in,
out or off. You can also access communications open/close events, view messages
sent or received, or determine when new content has been downloaded for transfer to
an aircraft."
(of course ACRS must be ON/active!!!)