GI-275 and magnetometer for revisionary mode

[Ragsf15e]

8 hours ago, shawnd said:

Turns out I have a spare GMU-11 from the anticipated older GI-275 setup. Will ask the shop to see if I can have this be installed in the right wing (left one has the GMU-44). And if not, then help me find a better backup solution. Though I agree with @PT20J, the vertical card compass is the last resort in case of electrical failure that would affect the GTNs as well as rest of the avionics once the battery dies.

I might just (vfr) pull your pfd circuit breaker and see what you really have.  The gi-275 is going to fall back to track vs heading which is just as good or better.  You can also turn off your gps and replicate electrical failure.  If the internal gps in the -275 is on you still get track.  I’m not sure how another gmu improves this?

[shawnd]

My panel is far from being finished at this point so can't do any manual tests. But yeah, after thinking about it, doesn't make much sense. We are trying to come up with a plan for 2 failures - PFD and electrical. Most likely will be one or the other, but in case both do fail, should have enough navigation capability to land somewhere quickly.

[PT20J]

I think it is important to have a philosophy when designing a panel because there is so much available that it is easy to get carried away. 

In my case the driving force was reliability; I was tired of playing whack-a-mole with old avionics. I designed to protect against only single failures. The new equipment is so reliable that I reasoned the joint probability of two failures on a single flight was nil. But, every piece of equipment will have some finite failure rate and I wanted to minimize the installed equipment to maximize the reliability over my period of ownership.  Others may certainly have different philosophies that might drive different decisions.