Hi Rampil!
In the EASA world most certificated small light VFR aircraft are required to
have
the bare minimum of three mechanical instruments, altimeter, ASI and compass.
As far as I've managed to read (I'm lazy so I don't spend too much of my
retirement
time wading through documents) EASA and our CAA don't cover this topic
i.r.o. permit (experimental) VFR aircraft. That seems to be left up to the LAA
who do insist on aircraft heavier than "microlights" (ultralights) having at
least the basics.
I can agree that the requirement for mechanical instrument back-up is
unnecessary
if a VFR light aircraft has at least two EFIS screens powered from independent
sources and that it is possible to transfer displayed information from one
to the other in event of power and/or screen failure.
However the aircraft which I've been asked to flight test for initial permit
issue
has only one EFIS screen and power source including the aircraft battery.
If there were no back-up of any description and the screen were to fail, then
the pilot would be sitting in an aircraft without flight information.
In the above situation you and I would probably manage to land happily enough
"by
the seat of our pants" and if a GPS was displaying groundspeed, then a safe
landing could more easily be made provided that the aircraft was facing into
wind. But perhaps an inexperienced pilot would be daunted.
My final 6 years before retiring from commercial aviation included 4k hours
flying
in an all-glass cockpit, where even the back-up was a neat little EFIS. I
love the modern stuff, but feel that it should have some sort of back-up.
Light aircraft in the LAA world are not required to have certificated
instrumentation.
As regards EFIS reliability, on average during those final 6 years I experienced
one screen failure each month (there were 2 main EFIS in front of each
pilot) and a couple of times before retiring I experienced multiple screen
failures. Our MEL allowed us to depart on IFR flights with one dead screen and
three out of four could be dead for VFR departures. Often a dead EFIS could
be brought back to life by rebooting.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=455131#455131
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