Colyn,

  He has the Dynon EFIS as backup. Do you not consider a second independent EFIS with it’s own ADAHRS as sufficient backup ?

  I am considering the same idea. Quite Glass

No not at all.

data points:

- mems based systems have only recently become "reliable".  mems is based on a tuning fork which is part of the chip.  when you accelerate the platform the tuning fork changes frequency.   The frequency change is mapped to an acceleration which is integrated into your current attitude/speed.   early on, failure to provide adequate mechanical isolation from vibrations caused inappropriate response in the mems system.   I can believe Chelton has beat on this problem pretty hard.  What's it take for a Dynon to guarantee that their system works in your airplane?  If you get past the mems part, you still have a computer, a lot of connections, another computer, and a display, all of which have to work flawlessly or you have no information.  As I said in a recent post, my venerable garmin 530 display in my cessna failed recently after 5 years of service.  It was sudden and complete, and Garmin still hasn't figured out what went wrong.  incidentally my infamous rc allen electric ai in my cessna outlasted the garmin

- failure analysis of computer systems is a combinatorial problem.  If you sell enough of them (e.g. 10's of millions a year) you get some back that failed because of really bizarre situations like multiple simultaneous but unlikely events, coexistence with unexpected other equipment, proximity to large voltage transients etc.   none of these ever happen in airplanes, right ;-)

- generally large volume chip/computer companies do a massive amount of testing which likely exceeds the entire run time of the entire production run of a company like dynon

- the bugs that slip through the massive testing  are returned by (the even more massive) customer base and the bug gets fixed.  some companies have a big farm of testing machines.  when they get a failure from the field they add that configuration to the farm and use it to test the next chip.

- failure modes of these kinds of systems are generally sudden and total.

- lightning happens

- even if the efis itself is infallible, it is still dependent on your power system.

Now consider your old mechanical AI.

It has a rotating mass and some needles.

It's a very fallible thing but it's failure mode tends to be gradual.

In my airplane I have an electric ai with an internal battery backup and a vacuum ai which depends on the engine

and an electric hsi and a vacuum dg

and an electric turn and bank.

so to be out of luck I have to lose one of the following combinations:

- both ais, both dgs

- both electric systems, the ai backup battery, and the vacuum pump or engine

- both electric instruments and the vac pump or engine

computers fail, and one of the failure modes is common between your dynon and your main displays, namely something gets zapped in your power system and perhaps every box that is attached to it.