Michael wrote:

First off, with dual AI's next to each other, I believe that following
a dying AI into an unusual attitude becomes far less likely, and thus
while the chances of recovery from the unusual attitude are reduced
slightly, the chances of encountering it in the first place are reduced
dramatically.Â*Â*NotÂ*soÂ*withÂ*aÂ*backupÂ*vacuum *-Â*youÂ*haveÂ*toÂ*engageÂ*it.

This is the first of my two major reasons for preferring the backup AI. It
helps with problem detection. A backup vacuum doesn't.

And even if you do, half the time (in my experience more) the problem
is the AI, not the power source, so backup power for the AI does you no
good.

And this is #2.

Some people to whom I've spoken about this have made a big deal about the
fact that the backup AI does nothing for a HI during a vacuum failure. My
response is typically "who cares?". Given a compass and a GPS, the HI has
plenty of backup already.

- Andrew