As a rule of thumb in doing ‘Failure Analysis’ on your installation: we want to look for potential ‘single point’ failures, and eliminate them to the extent possible (reduce their probability); or make the system tolerant by having a backup.  We normally do not need to assume double or multiple failures.  That usually results in added complexity, weight, etc., with little gain.

An example might be; if you have dual batteries as power source, you don’t need to pursue dual alternators.

Just thought I’d throw that out there.

Al