DA 42 accident

"Dylan Smith" wrote in message
...

I know a pilot who had a double magneto failure, too, which resulted in
the C172 on its back in a field. Guess what - most two magneto engines
have single points of failure.


What caused the mags to fail?

On 2007-04-26, Maxwell wrote:
What caused the mags to fail?

I don't remember the specifics (and I'm trying to find the NTSB report
with no joy so far). I believe it was one of those 'dual mag'
installations and there was a mechanical failure.

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"Maxwell" wrote in message
...

"Dylan Smith" wrote in message
...

I know a pilot who had a double magneto failure, too, which resulted in
the C172 on its back in a field. Guess what - most two magneto engines
have single points of failure.


What caused the mags to fail?


Obviously, I am not familiar with the particular case; but here are a couple
of scenarios:
1 There is a single gear which drives the entire accessory section.
2 There is/was a product called a dual magneto, used on some four
cylinder Lycoming engines which had an internal gear to drive the two
magneto sections and impulse coupler(s). There were several failures on
relatively new Piper Tomahawks in the early eighties.

Additional possibilities include shorts behind the instrument panel, or even
in the ignition switch or switches--since a magneto is dissabled (turned
off) by shorting the P-lead toground.

In addition to the magnetos; common failure modes include mixture and
throttle control cables and fittings.

Like Dylan, I have found the automotive ECMs to be far more reliable in
service than the old breaker ignition systems. I have had a defective
throttle positioner which resulted in a higher than normal idle speed, and a
rough running engine due to a defective spark plug, but nothing that
disabled the engines. So, personal feelings aside (which I admit is another
issue), the ECMs and FADECs seem to have better long term reliability than
the mechanical/manual systems they replace--and they may far fewer mistakes
than I do.

Peter

"Peter Dohm" wrote in message
.. .
..

Additional possibilities include shorts behind the instrument panel, or
even
in the ignition switch or switches--since a magneto is dissabled (turned
off) by shorting the P-lead toground.

In addition to the magnetos; common failure modes include mixture and
throttle control cables and fittings.

Like Dylan, I have found the automotive ECMs to be far more reliable in
service than the old breaker ignition systems. I have had a defective
throttle positioner which resulted in a higher than normal idle speed, and
a
rough running engine due to a defective spark plug, but nothing that
disabled the engines. So, personal feelings aside (which I admit is
another
issue), the ECMs and FADECs seem to have better long term reliability than
the mechanical/manual systems they replace--and they may far fewer
mistakes
than I do.


But that's a completely different kettle of fish. I was wondering what cause
the dual mag failure on a 172.

On Apr 26, 1:29 pm, "Peter Dohm" wrote:
Like Dylan, I have found the automotive ECMs to be far more reliable in
service than the old breaker ignition systems. [...]

grin That's because neither of you have had a failure yet. I've
had automotive computer systems fail due to cold solder joints, part
failures, sensor failures. Even had a transmission computer decide
to go into limp mode just because a sensor glitched for a few
seconds. If I were out in the woods, I'd much rather have old-style
points act up, than have a computer failure.

(Throttle positioning sensors don't count... the throttle is still
mechanical in that case.)

Mind you, every day I'm glad that my vehicles start instantly because
of electronic engine aids. But I'm not so happy about my wif'e's Land
Rover with fully electronic gas pedal. It's already had a recall
because the software could glitch and go into full throttle mode.
Yes, that could happen mechanically as well, but that you can fix
yourself on the side of the road!

And as I've opined before, I'm not looking forward to cars with fully
electronic brake pedals and steering wheels. shiver Not in my
lifetime, anyway ;-)

Regards, Kev

"Kev" wrote in message
oups.com...
On Apr 26, 1:29 pm, "Peter Dohm" wrote:
Like Dylan, I have found the automotive ECMs to be far more reliable in
service than the old breaker ignition systems. [...]

grin That's because neither of you have had a failure yet. I've
had automotive computer systems fail due to cold solder joints, part
failures, sensor failures. Even had a transmission computer decide
to go into limp mode just because a sensor glitched for a few
seconds. If I were out in the woods, I'd much rather have old-style
points act up, than have a computer failure.

(Throttle positioning sensors don't count... the throttle is still
mechanical in that case.)

Mind you, every day I'm glad that my vehicles start instantly because
of electronic engine aids. But I'm not so happy about my wif'e's Land
Rover with fully electronic gas pedal. It's already had a recall
because the software could glitch and go into full throttle mode.
Yes, that could happen mechanically as well, but that you can fix
yourself on the side of the road!

And as I've opined before, I'm not looking forward to cars with fully
electronic brake pedals and steering wheels. shiver Not in my
lifetime, anyway ;-)

Regards, Kev

There are a lot of new "features" that can keep me driving and flying the
old ones as well. And I am just about old enough to make that a viable
option--expecially for aircraft.

Peter

At one time there was a single drive to a Tee connector that drove both
magnetos. Stupid design that probably met some budget requirement with no
regard to why there were two magnetos to start with.

Dylan's statement that "most two magneto engines have single points of
failure" surprises me unless he's talking about other components. A properly
implemented two magneto setup is fully redundant.

--
Jim Carter
Rogers, Arkansas
"Maxwell" wrote in message
...

"Dylan Smith" wrote in message
...

I know a pilot who had a double magneto failure, too, which resulted in
the C172 on its back in a field. Guess what - most two magneto engines
have single points of failure.


What caused the mags to fail?

On 2007-04-27, Jim Carter wrote:
Dylan's statement that "most two magneto engines have single points of
failure" surprises me unless he's talking about other components. A properly
implemented two magneto setup is fully redundant.

That big gear at the back of the engine that drives the mags is a single
point of failure. While it is a very robust object, it's still driving
both mags.

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That big gear at the back of the engine that drives the mags is a single
point of failure. While it is a very robust object, it's still driving
both mags.

There are a few significant differences between this SPOF and the DA42
electrical SPOF. That big gear is =part= of the engine (in the same
sense that the mags are part of the engine), and it does not drive
anything else. Were that gear to also drive (say) the air conditioner,
then the air conditioner could put unwanted stress on the gear and
possibly break it. This is what (I gather) could happen with the
DA-42's design, where the electrical bus in question is not =dedicated=
to the engine.

Jose
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On 2007-04-28, Jose wrote:
anything else. Were that gear to also drive (say) the air conditioner,

Well, that big gear usually drives the vacuum pump, and it's not unknown
that it also drives the generator or alternator.

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