LML Gang,
Thank you all for the quick replies so far on this
topic! There has been some good discussion on points of failure and the
importance of having a robust backup plan for primary flight
instrumentation. For some background, my plane has vacuum attitude and
DG, electric turn coordinator and the TruTrak autopilot that has its own gyros
(no dependence on other gyros). I have felt that this is a pretty good
set of redundancies. As soon as the autopilot crapped out (I view this as
my backup to the other gyros primary gyros) I set the wheels into motion to
make a 180 back into the clear and return home.
In a previous life I designed the standby instruments
(attitude, altimeter, VSI) for the Boeing 777. These were the first certified
non-mechanical (LCD) backup instruments in a transport category aircraft.
You would not believe the amount of testing and certification activity that
went into these things. That’s why they cost ~$30K each! Even
with all of that, it still made me nervous that there is no mechanical backup.
Because of my engineering experiences in the avionics
industry, I have stayed away from EFIS to date. However, the allure of
the benefits of EFIS is winning me over and if I build another plane it would
likely include a certified EFIS system like Chelton but would DEFINITELY
include a set of mechanical backups, no matter how tested the EFIS system
is. The acid test I ask myself about each instrument is: “If this
instrument failed in hard IMC, how would I proceed?” In the case of
EFIS or the VM1000, the loss of an “instrument” is the whole
thing! When I chose the VM1000 vs. discrete engine instruments I
consciously decided that I could deal with loss of all engine instrumentation
and finish the flight safely. My engine is a stone simple Lycoming 320, I
can lean it manually and can use the clock for fuel management. In the
case of EFIS, when that instrument fails you have just lost all of your
primaries. I cannot deal with that and MUST have backups of all the
primary flight instruments.
Now, on to what concerns me the most about my system:
==========================================
Is there a way for me to mitigate the problems I had
yesterday? I know that the electrical components that are designed with
the appropriate protection in them will do better and that was the case
yesterday. Is there something that I can do externally to the existing
“under protected” equipment that will give me better margins?
If I had a metal plane I could electrically bond all control surfaces and put
wicks on the trailing edges. Not an option with an e-glass plane.
Don’t even know how well the wicks really work in a carbon plane.
Would chokes, zener diodes, shielding, etc. help? My EE training is
primarily in the digital/computer area and is fading at that (I got the
Marketing lobotomy a few years ago :)
Thanks again for all the input!
Dan