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Erich_Weaver(at)URSCorp.c
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 Posted: Tue Apr 14, 2009 8:04 am Post subject: DO-160 and EFIS brownout |
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I noticed that the latest publication of the EAA rag includes a nice ad from the good folks at Grand Rapids Technologies for their EFIS. The ad claimed that they "exceed" DO-160 standards. Im not intimate with the details of DO-160 but recall Bob recently chiding EFIS makers for their failure to provide brownout protection in their otherwise wonderful products. Does brownout protection fall under DO-160 guidelines? If so, perhaps now is a good time for us to gently prod them toward compliance in view of their claims.
erich
[quote][b]
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nuckolls.bob(at)aeroelect
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| Posted: Tue Apr 14, 2009 5:52 pm Post subject: DO-160 and EFIS brownout |
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At 10:59 AM 4/14/2009, you wrote:
| Quote: | | I noticed that the latest publication of the EAA rag includes a nice ad from the good folks at Grand Rapids Technologies for their EFIS. The ad claimed that they "exceed" DO-160 standards. Im not intimate with the details of DO-160 but recall Bob recently chiding EFIS makers for their failure to provide brownout protection in their otherwise wonderful products. Does brownout protection fall under DO-160 guidelines? If so, perhaps now is a good time for us to gently prod them toward compliance in view of their claims. |
Yeeaaahhh . . . sort of.
When somebody says, "We meet or exceed DO-160 standards,
it can mean a lot . . . or very little.
DO-160 is not a standard. It's not a requirement. It's
a catalog of suggested investigative/proof tests for
demonstrating that a particular piece of equipment is
suited to the intended task. See:
http://www.aeroelectric.com/articles/DO-160.pdf
Obviously, we're more concerned about performance for
a heads-up display than we are about the battery bus
voltmeter. Environmental conditions in the forward wheel
well are light years away from those of the galley
warming oven.
So one of the first issues for purchasing any new
piece of equipment involves an agreement between the
buyers and suppliers as to what tests will be run
and under what levels of stress and what constitutes
a pass-fail condition.
The final agreement takes the form of a Qualification
Test Plan (QTP) that speaks to all those features and
is blessed by all interested parties before the program
moves forward.
When the "pass" condition has been demonstrated for
all tests, then a certain document is filled out
that may look a lot like this:
http://tinyurl.com/cvqth2
As you can see, this form has a place to speak to
the entire constellation of DO-160 tests. I'll call
your attention to notations for Section 9.0, 10.0 and
others where we're told that this feature is "Category
X, no test performed."
Further, there should be a mini-synopsis of the
qualification test form as part of the device's
product identification label where you will see
a string of characters like this:
[img]cid:.0[/img]
If you know how to decode this string, you can learn
a lot about how the device was tested. Note the
multiple appearances of "X" in the string. Those
are tests that were not performed. The other letters
speak to tests that WERE performed and to what
levels.
Sections 16.0 through 20.0 speak to a host of input
torments including power interruptions and brownouts of
various magnitudes and duration. The goal of performing
these tests is to show two things: (1) the input power
anomaly doesn't damage the device and (2) if the
device wanders into the weeds as a result of the
stress, it should demonstrate some "acceptable"
mode of recovery. Here's the ace-kicker. For some
products, it may be acceptable for the operator
to carry out some action to drag the device out of
the weeds. In more critical cases (like autopilots
or flight displays) we might agree that the screen
can glitch or the ailerons twitch but recovery after
the event is autonomous, timely and pucker-free.
With respect to your question about brown-out,
yes . . . there some tests that touch on that.
But without reading the test plan for a device
and knowing what the interested parties called
"acceptable recovery characteristics", the statement
that a product "meets or exceeds DO-160" has
a risk of being vague and/or not very satisfying.
In the case of a processor-based system parameters
display, the critter may go nuts during the event
but stand up in a few hundred milliseconds. I
think I could live with that. For the early
versions of Blue Mountain flight instruments
systems, the processor had to reboot from a
hard-drive. This could take some time and if
it happens in flight, raises questions as to
accuracy of the displays after they quit
thrashing around.
As you can see from this mini-dissertation on
equipment qualification, designing to live in the
sandbox with really big cats is not a trivial
task. Further, DO-160 speaks only to the effects
of environment. You still have to thrash out
an agreement on ability to perform the intended
task.
My occasional accusation that certain products
were "not designed to live in the real world of
airplanes" is not intended to be flippant or
demeaning. It was a simple observation of fact
that should give the OBAM aircraft builder pause
to insure that system integration into their
project is accomplished with understanding.
Back to your original suggestion: It NEVER hurts
to inquire as to exactly what DO-160 tests were
run and even ask to see a copy of the cert sheet.
If they've done a good job, they'll be proud to
show it to you.
Bob . . .
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