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EFIS Backup EFIS?
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bruceflys(at)comcast.net
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PostPosted: Wed Jan 04, 2006 8:38 am    Post subject: EFIS Backup EFIS? Reply with quote


Experimental EFIS units have matured in recent years to the point where many
of us will use one as a PFD. But has technology and reliability progressed
to where a second EFIS with an independent power source could prudently be
used to backup the PFD? For example, a pair of Dynon D-10A units could
serve in this manner and have the added advantage of a backup PFD
center/right that the co-pilot could see too.
For certificated airplanes the FAA requires (FAR 23.1311) as backups
separate mechanical or electronic airspeed, altimeter and attitude
indicators along with an independent magnetic direction indicator . While
much of FAR 23 is worthy of respect, this provision was written long-ago
(in
technology terms) and may be obsolete. And after all, we build
experimental
airplanes to use newer methods if safe and cost-effective.
My concern is for a failure mode that would take out both EFIS units or
their displays. Could a lightning strike do that? How about a severe
voltage spike? Would transorbs alleviate either? Are three electronic
indicators subject to the same failure?
Any thoughts will be appreciated, and TIA,
Bruce McGregor
GlaStar (panel and electrical system)


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bryanhooks(at)comcast.net
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PostPosted: Wed Jan 04, 2006 9:08 am    Post subject: EFIS Backup EFIS? Reply with quote


One thing to consider is what inputs are required to allow the EFIS' to
work. For example, if you have 2 EFIS units (lets say left and right),
both of which are made by the same manufacturer. Let's further suppose
that these units use airspeed as an input to their processor to aid in a
determination of attitude. If both of these units are attached to the
same pitot/static system, what do you suppose would happen with a
clogged pitot?
Gotta have redundant / independent inputs to get redundant / independent
outputs.
Just something that comes to my mind, right or wrong. Worth only what
you paid for it.
Bryan Hooks
RV7A, slowbuild
Knoxville, TN


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klehman(at)albedo.net
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PostPosted: Wed Jan 04, 2006 9:55 am    Post subject: EFIS Backup EFIS? Reply with quote


I consider your concerns quite valid especially when you consider the
software issues that continue to crop up. However I believe the main
reason for simple basic independant flight instruments on many large
ships is that they will continue to reliably run off the battery even
when everything else such as engines and inverters have gone offline. It
happens. Hopefully this FAR will stay in effect. Even automatically
deployed windmills for emergency hydraulics and AC electrics have their
limitations and do not come on line instantly. And when similar systems
disagree it is nice to have a totally different system as the tie breaker.
Ken
Bruce McGregor wrote:
Experimental EFIS units have matured in recent years to the point where many
of us will use one as a PFD. But has technology and reliability progressed
to where a second EFIS with an independent power source could prudently be
used to backup the PFD? For example, a pair of Dynon D-10A units could
serve in this manner and have the added advantage of a backup PFD
center/right that the co-pilot could see too.
For certificated airplanes the FAA requires (FAR 23.1311) as backups
separate mechanical or electronic airspeed, altimeter and attitude
indicators along with an independent magnetic direction indicator . While
much of FAR 23 is worthy of respect, this provision was written long-ago
(in
technology terms) and may be obsolete. And after all, we build
experimental
airplanes to use newer methods if safe and cost-effective.
My concern is for a failure mode that would take out both EFIS units or
their displays. Could a lightning strike do that? How about a severe
voltage spike? Would transorbs alleviate either? Are three electronic
indicators subject to the same failure?
Any thoughts will be appreciated, and TIA,
Bruce McGregor
GlaStar (panel and electrical system)


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Bruce(at)glasair.org
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PostPosted: Wed Jan 04, 2006 9:58 am    Post subject: EFIS Backup EFIS? Reply with quote


Yep, even the PSS AOA goes out to lunch when pitot pressure is interrupted.
This little flaw caused one crash, if I recall correctly.
The problem with 2 EFIS units are,
1) Are you scanning each to note any discrepancies?
2) If one disagrees with the other which one is right?
Bruce
www.glasair.org


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glastar(at)gmx.net
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PostPosted: Wed Jan 04, 2006 10:20 am    Post subject: EFIS Backup EFIS? Reply with quote


Bruce,
FAR 23.1311 point 5 describes mechanical instruments OR independent
electronic instruments.
You will reach that as example with a pair of Dynon's where the primary
has two different power sources and/or an internal backub battery.
Take care
Werner (one Dynon D10A with backup battery plus one uEncoder, no
mechanical instruments, VFR only)
Bruce McGregor wrote:
Experimental EFIS units have matured in recent years to the point where many
of us will use one as a PFD. But has technology and reliability progressed
to where a second EFIS with an independent power source could prudently be
used to backup the PFD? For example, a pair of Dynon D-10A units could
serve in this manner and have the added advantage of a backup PFD
center/right that the co-pilot could see too.
For certificated airplanes the FAA requires (FAR 23.1311) as backups
separate mechanical or electronic airspeed, altimeter and attitude
indicators along with an independent magnetic direction indicator . While
much of FAR 23 is worthy of respect, this provision was written long-ago
(in
technology terms) and may be obsolete. And after all, we build
experimental
airplanes to use newer methods if safe and cost-effective.
My concern is for a failure mode that would take out both EFIS units or
their displays. Could a lightning strike do that? How about a severe
voltage spike? Would transorbs alleviate either? Are three electronic
indicators subject to the same failure?
Any thoughts will be appreciated, and TIA,
Bruce McGregor
GlaStar (panel and electrical system)


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frank.hinde(at)hp.com
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PostPosted: Wed Jan 04, 2006 11:03 am    Post subject: EFIS Backup EFIS? Reply with quote


My plan is to engage the Autopilot if things get screwy in IFR...Just
hope that's right...Smile
Frank


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mprather(at)spro.net
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PostPosted: Wed Jan 04, 2006 11:04 am    Post subject: EFIS Backup EFIS? Reply with quote


<Bruce(at)glasair.org>
2) If one disagrees with the other which one is right?

The T&B (you didn't eliminate that, did you?)?? Smile
Matt-

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BobsV35B(at)aol.com
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PostPosted: Wed Jan 04, 2006 11:13 am    Post subject: EFIS Backup EFIS? Reply with quote



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PostPosted: Wed Jan 04, 2006 11:31 am    Post subject: EFIS Backup EFIS? Reply with quote



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Bruce(at)glasair.org
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PostPosted: Wed Jan 04, 2006 11:40 am    Post subject: EFIS Backup EFIS? Reply with quote


Do you really want to resort to needle, ball, and airspeed when you're 400
AGL coming down the ILS? Nope, need 2 independent systems and a third
attitude instrument. Of course, I don't have an EFIS in my GIII, just an
EHSI.
Bruce
www.glasair.org


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frank.hinde(at)hp.com
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PostPosted: Wed Jan 04, 2006 12:02 pm    Post subject: EFIS Backup EFIS? Reply with quote


Kinda sorta,
I should have explained further that my A/P is a pictorial pilot from
Truetrack, which has a solid state turn coordinator built into the
display head.
This is a backup to the EFIS which in turn is backed up by internal
battery.
So I have two independent attitude displays (atually 3 if you include
the companion engine monitor that can display the EFIS output, but it is
not a fully redundant backup)
Other backups are the ASI and altimeter steam guages. In addition to the
IFR GPS and Nav/com and backup comm radio.
See any problem with this for "light IFR"?
Cheers
Frank


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cjensen(at)dts9000.com
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PostPosted: Wed Jan 04, 2006 12:04 pm    Post subject: EFIS Backup EFIS? Reply with quote


Frank wrote........


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BobsV35B(at)aol.com
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PostPosted: Wed Jan 04, 2006 12:24 pm    Post subject: EFIS Backup EFIS? Reply with quote



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mprather(at)spro.net
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PostPosted: Wed Jan 04, 2006 12:30 pm    Post subject: EFIS Backup EFIS? Reply with quote


As I have said in the past, I tend to fly somewhat more precisely (maybe
more deliberately) without the benefit of the AI (needle, ball, airspeed).
I have to admit that the T&B in my airplane works really nicely - smooth,
with very little lag. Also, the airplane I fly is pretty stable in yaw,
which probably helps the instrument keep up - little yaw coupling in
turbulence..
The problem I have with AI's (mechanical or digital) is that it seems like
they head for the weeds with little indication that something is awry (the
low-cost ones, anyway). If I had confidence that the EFIS was going to
positively tell me when it's offline, then I might feel better about
installing 2 of the units (for redundancy). People are talking about low
cost EFIS units as their PFD when we aren't that far from reports of these
units developing the leans. If the failure mode of the device was to
simply turn off (go black), I'd be happier. I don't want to get into a
situation where I have to decide the fate of the flight by determining
which EFIS is wonky.
Finally, I would say that I am having a pretty bad day if my AI fails on a
flight where I have no choice but to fly an ILS to mins. In my book
(non-revenue generating airplane), that's the time to seriously consider
calling the missed, and going to my (hopefully) VFR alternate.. If you
are flying for money, the rules are different, and you may be able to
justify the higher cost EFIS units which have better fail modes.
Regards,
Matt-
<Bruce(at)glasair.org>
Do you really want to resort to needle, ball, and airspeed when you're
400 AGL coming down the ILS? Nope, need 2 independent systems and a
third attitude instrument. Of course, I don't have an EFIS in my GIII,
just an EHSI.
Bruce
www.glasair.org


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BobsV35B(at)aol.com
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PostPosted: Wed Jan 04, 2006 12:38 pm    Post subject: EFIS Backup EFIS? Reply with quote



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Bruce(at)glasair.org
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PostPosted: Wed Jan 04, 2006 12:41 pm    Post subject: EFIS Backup EFIS? Reply with quote


Light IFR, what's that?
Let's take a look at our flying environment. These pocket rockets we build
are, by most part, neutrally stable. By that I mean that the airplane will
stay where you point it when you let loose of the controls. This is what
makes them so much fun to fly. It also means that they are a handful to hand
fly IFR. Can you, sure - if you have everything at hand, all your charts in
the right order, and your approach plates memorized. Or, you have a
functional autopilot.
The point I'm trying to raise is that even the most trained pilot is going
to have flight path excursions when transitioning from full to partial
panel. You want that transition to be to a true attitude instrument, not a
T&B. This would, at least, minimize the excursions. Can you shoot a needle,
ball, airspeed ILS approach - sure can, if and it's a big if, I had
transitioned to N/B/A before I started the approach. I doubt if I could
transition at mid-approach without major excursions.
The T&B is not a precision attitude instrument. It's sole purpose is to save
your butt long enough to find some VFR conditions.
Bruce
www.glasair.org


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Bruce(at)glasair.org
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PostPosted: Wed Jan 04, 2006 1:01 pm    Post subject: EFIS Backup EFIS? Reply with quote


Hi Bob,
I don't have a third attitude gyro, I have a Sandel 3500 EHSI, and a vacuum
powered attitude gyro/FD, I also have a PN101 HSI as my second nav head. My
vacuum system has a backup and a visual/audible alarm. My STEC 55 autopilot
will fly a coupled ILS approach without the attitude gyro. And if all that
fails I still have N/B/A.
Last time I ran a tape, I had around 150k in my Glasair III, not a lot by
today's standards.
You're free to fly with any form of instruments you desire. Charge of into
hard IFR with a Dynon and a T&B. Your choice, just understand the
consequences and limitations. Too many flights end with the pilot saying "OH
SHIT" followed by the sound of ground impact.
Bruce
www.glasair.org


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rvbuilder(at)sausen.net
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PostPosted: Wed Jan 04, 2006 1:04 pm    Post subject: EFIS Backup EFIS? Reply with quote


One of my many concerns is how to provide adequate backup for instrument conditions in my RV-10. There really is no substitute for the old mechanical ASI, T&B, and Alt along with a magnetic compass. However I feel that the likelihood of a total electric blowout is fairly low not to mention with an electrically dependant aircraft I will have a bigger issue. So based on that, my current plan is for something along the line of a modified Z19 but without mechanical instruments.
I am currently planning on a two screen Chelton with one screen on the main bus and the other on the ebus. The single Chelton AHARS will be fed from the engine and main battery buses in a arrangement similar to the ECU and fuel pump to minimize the chances of a reboot during an electrical failure. I will use a BMA G3 Lite for the backup instruments powered from the ebus. In an absolute worse case scenario where everything goes dark I will have my Garmin 196 and handheld radio for last ditch backup.
This may not be a perfect configuration that caters to 100% of all failure modes but I feel it will cover 99.9% of them to get me down in one piece.
My $0.02
Michael Sausen
-10 #352 Fuselage
Do not archive


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frank.hinde(at)hp.com
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PostPosted: Wed Jan 04, 2006 1:12 pm    Post subject: EFIS Backup EFIS? Reply with quote


Hence the Auto pilot!
Frank
Do not archive


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frank.hinde(at)hp.com
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PostPosted: Wed Jan 04, 2006 1:18 pm    Post subject: EFIS Backup EFIS? Reply with quote


Ha....Comfortable with it..hell no, I have ten hours in actual IFR
conditions and a scary flight in the rear seat of a newly minted IFR
jock forgetting to adjust his DG for precession...I mean he adjusted it
like 10 minutes ago...should be fine right...as long as your comfortable
with a 15 degree error it is yes....Piece of junk!
My aim is to get instruction for my instrument ticket in my
RV7A....These maybe famous last words! As I rent a doggy old (but
stable) spam can....Smile
Frank
P.s Al Haynes is a fascintaing guy to listen to when it comes to
DC10's...Smile
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