@Ian_W
Precisely right!
If the ACARS went through a normal log-off sequence then it was shut down deliberately. If it just stopped reporting then it could have been some other reason. As it has been said multiple times 'the ACARS was deliberately switched off' that implies that it went through a log-off sequence and tidy shut down, something it would NOT have done if the power to it was cut by the circuit breaker being tripped.
ACARS log-off from the cockpit is a reasonable interpretation that fits two stated facts:
- cessation of normal ACARS data
- multiple hourly SAT data link connections with no buffered data to send
For those in the catastrophic failure camp - I haven't seen
ACARS - LOGGED OFF in the various emergency procedures stated here so far.