"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