On the other hand, to hold that
an all electronic system has as favorable probability numbers as electronic
plus mechanical backup is not a matter of personal comfort level. It's
just not a correct statement of the facts.
Colyn, This statement can very well be true or false.
You must always evaluate failures as a system. Identify
where failures can happen and confirm that you have a backup and/or can LIVE
with the failure.
I could easily IMAGINE scenarios where an aircraft with an
electrically dependent engine and mechanical gauges is more likely to have serious
risk mitigation problems then an aircraft with a non electrically dependent
engine and only electrical instruments.
You can have a false sense of security if, for example, some
of your mechanical devices are electrically dependent and your failure mode
takes out it’s electrical source.
Vacuum systems are far more likely to fail than non vacuum
systems. So when you really need them there is more likely a probability they may
have their own failures.
An all electric backup, that has no system coupling to the
primary systems (i.e. independent power, transducers, wire harness, connectors,
etc.) can be as reliable in a “System” context to those systems that
you IMAGINE with mechanical backups.