"Kelly" writes:

I would be interested in getting opinions about backup systems for a
vacuum pump failure and/or AI failure. I have a 172P [...]

Considering the nature of the 172, you likely don't engage in too much
heavy duty IMC, so backup equipment could be of the "help me land now"
kind rather than "help me fly for a few hours more" kind.

[...] While I haven't seen the panel page/"6-pack" page on the 396
or 496, I have read (in Aviation Consumer) that it's good enough to
keep control of the airplane in an emergency situation. [...]

You should also consider the iQue3600a, which has essentially the same
aviation features as the 396, at half the price, and with ground-side
utility as PDA and car GPS. (The other backup technologies you
mentioned have no separate ground utility.)

In any case, you should test it out. Borrow someone's
296/396/496/iQue or other portable aviation GPS, set it up in your
cockpit, go under the hood and do some partial-panel with a mostly
covered-up instrument panel. An hour or two might suffice.


- FChE