In the interest of stimulating discussion on panel logic, this is something I don't understand. Modern EFISs are very reliable, I don't know the precise failure rate but if we could see the numbers I think we'd see that it's about as probable as your engine quitting. I'd bet that most of you still building will have a GPS in the panel also and there's a good chance it will be a Garmin 396/496. If so then the GPS provides groundspeed, GPS alititude, and even a mock instrument panel. The Garmin also has built in battery back-up. Should the EFIS ever go down, either by failure itself or failure of the ship's entire electrical system, just use the GPS to fly to the nearest airport.

So, here's the question for debate: why add the expense, weight, and complexity of backup ASI and altimeter on a VFR-only aircraft? Thoughts & opinions?