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Tim Olson
Joined: 25 Jan 2007
Posts: 2879
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 Posted: Thu Aug 23, 2007 9:12 am Post subject: Interesting comments about EFIS's in current thread on Lanca |
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This a.m. I saw a real thought provoking thread start up
on the Lancair List. I'll repost the early part of it here
because it has some great thinking points that some people
may be interested in.
--
Tim Olson - RV-10 N104CD - Flying
do not archive
-----------------------------------------------------
Colyn writes:
<<Yesterday I was out for a lark and the screen display gradually
disintegrated just like in the movie "the matrix". I hadn't
internalized how dependent I was on this piece of equipment until it
wasn't there. <snip> Anyway, maybe Brent can correct me, but I assume
if a Garmin can break, a Chelton can break.
I hope you Chelton drivers are ready for it when it happens.>>
--
Brent agrees with you! Brent understands that anything can, and
therefore will, break and you MUST have a plan for when that happens.
That is why the Chelton systems are designed as recursively redundant
units. Each display is identical to the others and the architecture of
the communication ports is such that if one screen dies then the next
one automatically steps up and takes over. So you do not need to hope,
Chelton drivers ARE prepared if a display goes Tango Uniform. Two
redundant screens beat one big screen every time.
Even if you do everything right , there are still unseen forces at work.
Our planet is constantly being bombarded with high energy particles
(Cosmic Rays). When one of these particles hits a memory cell just right
it can cause it to flip (google "single event upset"). If the right cell
flips it can cause the processor to hang or crash. While this does not
happen very often, there are billions of memory cells and the Cosmic Ray
flux increases dramatically with altitude. This is why we designed the
Chelton systems with Error Correcting Code (ECC) RAM. I know of no other
system available to the experimental market that has ECC RAM. In
addition, all Chelton systems (and sub systems and sensors) have
independent hardware watchdogs that reset the entire system in the event
of the flight software hanging or crashing.
On the topic of software, in flight mode the Chelton systems do not
have or use an "operating system". The Level A certified flight code
does all the required functions. It even gives the BIOS the boot after
boot. Certifying a Microsoft or Linux style OS to level A would be about
as easy as making water that wasn't wet. Chelton does use a DOS -like
environment only in ground maintenance mode.
The next thing to worry about is a total aircraft power failure. All
electronics require power so if you take the power away..... This is why
smart builders have standby gauges IN THE SCAN and those gauges are the
good old fashioned mechanical ones. They operate on different physics
than the fancy glass and will likely survive whatever kills the
computers. Don't forget a UPS for the standbys. Harry League has a great
example of a nicely arranged panel. Harry, how about a picture? I know
you are camera shy.
While I am on a rant, here are some glass myths that need to die:
"The best instrument panel would be a 42" plasma monitor." Bigger is not
intrinsically better. This is coming from someone who is just under two
meters tall and a hundred kilos (bet you didn't know they could stack
sh*t that high). What is better is to have the critical flight
information as clearly as practical is the smallest visual arc. Fix your
vision on this point * and see how may words you can read around it
without moving your gaze. You get an idea as to the small size of the
fovea cenrtralis. Flight information needs to be clear and concise. When
a big screen goes dark, all you have is a big loud nuthen, unless it
also controls your radios.
"Detailed terrain graphics is a good thing." Detailed graphics hog
resources. Resources that would be better used to provide a faster frame
rate, storing a larger terrain database, processing sensor data and
performing useful housekeeping tasks like checking the validity of
incoming data and the accuracy of displayed data. Besides, the FAA is
very particular about display colors. Getting them to accept the graded
sky was a big push. Displaying photo realistic terrain is a non-starter.
How are you going to guarantee that the terrain "pattern" will not form
a "symbol" that could be interpreted by the pilot as "false or
misleading" information. As with animals in clouds or the face on Mars,
the brain wants to make sense from chaos. The last thing you need is a
Rorschach EFIS. You can avoid an ugly brown mountain just as easily as a
pretty textured hillock. It would be a shame if the processor crashed
while painting that pretty picture and the last thing to go through your
aesthetically pleased mind was the rudder.
"We are introducing our new EFIS. It will be certified in 6 months and
cost 5 grand." The only this that gets through the FAA in 6 months or
less is coffee and doughnuts. Not only is getting certification hard,
it is getting harder as the FAA is getting smarter...er...well.. more
experienced. Graphics processors and programmable logic devices now
raise enough red flags to make Lenin feel homesick. It would take at
least 2 years and 3-5M$ to certify an all new EFIS and the software to
run it. If you sold a 1,000 units then you would need to allocate $5K
per unit just for amortized certification costs. Add cost of goods,
marketing , overhead, insurance ..... and operate at a modest 50% gross
margin and all of a sudden $30K per screen seems pretty reasonable. If
it seems too good to be true......
With the nearly ubiquitous availability of industrial single board
computers, high brightness color displays, RC model AHRS and flight
simulation software, an EFIS that draws slack jawed oglers at trade
shows can be built by any idiot, and they frequently are. But aren't
idiots a valued resource? After all, doesn't every village need one?
Yes Timmy, but would you trust your life to one?
Speaking as an idiot who did those very things, thirteen long years
ago, trust me when I say "Don't trust what you hear or read."
Follow these rules, even if I am wrong it can't hurt:
Believe nothing a marketing person tells you.
Fly before you buy.
If it is a "future upgrade" assume it will never happen.
Plan for when it breaks.
Regards
Brent Regan
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Dick Sipp
Joined: 11 Jan 2006
Posts: 215
Location: Hope, MI
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| Posted: Thu Aug 23, 2007 7:31 pm Post subject: Interesting comments about EFIS's in current thread on Lanca |
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To add to Brent's comments (thanks for posting them Tim) I have seen million
$ certified EFIS systems die in top of the line corporate jets. In one
case it was attributed to too much heat build up. Ample time was spent in
the simulators dealing with EFIS failures at the worst possible times.
Another area that deserves consideration is the prospect of flying GPS
approaches with avionics that do not have
all of the required integrity monitoring, position refresh rates and
appropriate annunciations. I certainly can not explain everything required
but recommend Keith Thomassen's excellent manual for starters.
Dick Sipp
N110DV 40065
Finishing frenzy
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