>One of the things that I have heard people say, is that auto fuses would be
>OK most of the time, but you don't have an easy way to identify which fuse
>blows while in flight. I had been thinking about ways to wire up a failure
>indicator LED when I happened to notice the solution hanging on the rack in
>the auto fuse section of a TRAK auto store.
<snip>
What value is there in knowing that a fuse has blown? The reasons
that some device in your airplane fails to function range from
simple disconncts to end of life (bulb burns out, brushes worn,
etc.). Very few system failures result in opened circuit protection.
So what value is there in knowing that something doesn't work because
the fuse is opened or that it's some other problem that didn't
open the fuse? In either case, the system doesn't work and
plan-B has to be implemented.
What is the first indication pilots have that something is
amiss? You flip a switch and the expected thing doesn't
happen. A flag drops on an instrument. A pointer goes to
zero . . . considering ALL the things that will produce
the same dead system, why is is useful to know that a fuse
is popped? And if it were popped, do you really want to
replace it in flight?
I wonder if the annunciator panel recently added to the
EXP-Bus hasn't fueled new anxiety amongst our fellow
builders. First the product offers to replace electro-mechanical
breakers having lots of parts with solid state breakers
having only one part. Good . . . parts count down, reliablity
up and cost is down. Now it adds an annunciator system
to show when a circuit is functioning. Parts count
up, added cost, and light bulbs can lie.
Consider how many C,B or P single engine airplanes have
an indicator light to show that the landing light is on?
Fuel pump running? Pitot heat on? None that I've flown.
How do we know if those things are working? Ammeter goes
up, runway is visible, fuel pressure is up. If the system
dies, does the annunciator light go out? No, it powers up
from the same souce as the device . . . flip the switch,
the annunciator light comes on and something MAY work.
Suppose any of those devices is bad, the annunciator is
still on. Or in the case of your suggestion about
the fuse annunciators, the fuse is still good.
So the question remains, what value is there in
annunciating breakers popped, fuses good, or power
switch closed when there are failure modes that
the annunciation doesn't catch.
I'll suggest you're better off using system performance
results to tell if things are working than to waste
time, money and misplaced confidence in any form
of annunciation that has no way to make your experience
any safer. Worse yet, it may detract from safety by being
a distraction or providing misleading information.
Bob . . .
////
(o o)
< A mind abhors a vacuum . . . >
< When deprived of facts, >
< our fantasies are generally >
< much worse than reality. >
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