>Date: Wed, 29 Oct 1997 09:31:33
From: "Robert L. Nuckolls, III" <nuckolls@aeroelectric.com>
>Subject: Re: Master Switch
>
>>Bob,
>>
>>First off I visited your web site, it's great. I'll kindly explain why
>>I, others and many manufactures feel an avionics master switch is useful.
>
> . . . there's a difference between "useful" and "necessary" . . .
>
>> First off, it's nice to be able to turn on everything with just one
>>switch but that does have it's draw backs as you know.
>
> . . . not the least of which is single point of failure for every
> electronic item. Further, contemporary bus architectures don't
> accomodate essential goodies with a second, totally isolated
> power path . . a few folk have installed a second switch across
> the first path, "just in case."
>
>> . . . . I'm not sure just
>>how much avionics you've installed but my guess is very little.
>
> True. I've not been personally involved in installation of
> off-the-shelf products in many airplanes . . . perhaps a large
> gap in my education or I would have discovered earlier how
> bad some of these products are, to wit:
>
>> . . . . . . If
>>you've ever installed a GEM, IIMorrow 360, Shadin air data computer or
>>BFG 900 in a 4 cyl Lycoming powered aircraft and started it with the
>>avionics on you will scramble the software and at least one of the above
>>items. Often you can reset the instrument by just shutting the avionics
>>master switch off and then back on.
>
> Why do you purchase and install this kind of stuff in your airplane?
> As I mentioned earlier, I've been designing electronics systems for
> aircraft for a long time (25+ years). The gizmos ranged from simple
> low voltage warning systems to a servoed trim speed controller
> that's currenty flying on the majority of the Lear fleet. I'm a
> consultant to several manufacturers of modern, microprocessor
> based components for aircraft and other vehicular applications
> (you can't escape them any more, microprocessors are everywhere).
> This type of behavior is unacceptable to my customers and unacceptable
> to me as a designer. If you don't box these things up and send
> them back, you've told your supplier that his design is "acceptable".
> If the computer on which I write this barfed like that more than
> a few times, it would be back in the box . . . or at least worked
> on to fix the problem. My microprocessors don't go dumb with every
> hicup on the bus, why should I accept it that anyone else's does?
>
>> . . . . . If the battery is weak, then the
>>problem is worse. I haven't seen avionics software scramble with the
>>master switch left on as much with the big bore continentals. This is
>>probably because they are 6 cyls and low compression. Put and "O" scope
>>on the avionics buss and start a Lycoming, you will see spikes not just
>>low voltage.
>
> How "big" and for how long?
>
>>I don't think radios were designed to work during most piston aircraft
>>starting, this is not ordinarly. I sent Mike Busch a couple of notes
>>from King and Collins stating that an avionics master was desired. . .
>
> I'd like copies of those letters . . or the name of the person
> at the bottom.
>
>>DO-160 is not revelent to all avionics such as GEMS and sorts.
>
> DO-160 is relevant to any piece of electrical equipment the manufacturer
> chooses to apply it to. It's not a specification but a test method.
> If you have any gizmo capable of being an antagonist or victim to
> other equipment, DO-160 outlines test methods for various conditions
> found aboard an airplane. It's applicable to ANYTHING you want
> investigate for suitability of use on aircraft.
>
>> . . . . . I don't
>>know of any current aircraft that doesn't have an avionics master from
>>the factory, even the new Cessna models. I just got out of a Citation 5
>>and the check list had "Avionics Master Off" BEFORE the start button was
>>pushed.
>
> I don't doubt it. I was working at Cessna when we put the first ones
> in the airplane and based on what we knew then, the fragility of the
> radios, the lack of design standards, and the general attituded that
> "more gizmos is better" I thought it was a good idea then too. The
> thing that mystifies me is why, in 30 years since, we've not
> learned as designers to do any better and why as consumers, we
> put up with what ever the manufacturer wants to sell us.
>
> After designing to meet performance specifications, the #2 design
> item on my list is stand up to EVERYTHING the airplane can throw
> at me. I can also tell you that the task is trivial compared to
> other design requirements. I just finished qualifying a new
> autopilot for a military program. This piece of hardware would
> survive quite nicely in any single engine airplane too . . . the
> autopilot costs about $9,000 to build. The cost of components to
> insure survival from bus induced hazards is under $10.
>
>>Is an avionics master needed??? In my opinion it is, nor will I do an
>>installation without one but you definately can have your own opinion.
>>That's called America:)
>
> But here's the ace-kicker. The avionics master switch is a
> check-list item. I cannot count how many times I've stepped into
> a rental airplane and found the avionics master switch still on. If
> a missed or ignored check-list item truly puts some very expensive
> part of the airplane at risk then I'll suggest there's a SERIOUS
> design problem here, would you disagree? Don't pilots have enough
> responsabilites as pilots without burdening them with guardianship
> of fragile or balky electronics? In virtually EVERY segment of
> consumer electronics from Matel Toys to the fire-breathing, byte
> thrashers on my desk, the value and capability of electronics-for-
> the-people gets better almost daily. Yet we as pilots and owners
> of airplanes take it in the shorts because there's some aura about
> "aircraft quality" or "certified" hardware that has put our best
> senses as consumers to sleep.
>
> You say you have documentation from manufacturers wherein they
> recommend an avionics master switches. You also allude to special
> action on the part of the pilot to coax pieces of equipment into
> normal operation. Wouldn't it be better to encourage, nay INSIST
> that manufacturer to live up to a trivial responsability? A 1960's
> attidude of avionics consumerism puts little pressure on them to
> do better. I work with hundreds of individuals who are assembling their
own
> airplanes. We design and fabricate systems that are failure tolerant
> and free of trash that exceeds the capability of DO-160 qualified
> stuff to SURVIVE. Since we're building the best single engine airplanes
> that ever were, I counsel my friends to not tolerate any lapse in
> supplier responsabilities to provide equipment suited to the task.
> This includes both matters of survivability and operability.
>
> Your constituency is pretty much stuck with "what you see is
> what you get" from the aircraft manufacturing community. Customer
> relations of these firms may claim to have customer's best
> interests in mind but I'll suggest they demonstrate otherwise.
> When the kind of products you describe are allowed to continue
> to flow into new applications, it's a glaring example of breakdown
> in supplier consumer relations and manufacturers responsabilities
> to REDUCE pilot workload not increase it.
>
> I really like to get some names of contacts you can supply for
> any firm that suggests that an avionics master switch is useful.
>
>
Bob . . .
AeroElectric Connection
////
(o o)
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