"John Galban" wrote in message m...

What does a single impulse coupling have to do with liability and
the risk of injury? Most of the singles in the fleet have a single
impulse coupling on the left mag only.

And because impulse couplings fail. What's not there can't fail. That
argues for only having one (as opposed to the OP who wants two).

It's really a safety feature? That's a new one on me. As far as I
know, the impulse coupling retards the spark to enable the engine to
start at low rpm. It also gives the mag a quick "spin" to increase
the power of the spark. If you have no coupling, you get no start
(unless the plane is equipped with a "shower of sparks" system).

You don't even have to have an impulse coupling, the coupling just gives
you a stronger spark (since the mags are pretty weak even when
turning at full speed). You may need this if you've got less than
optiumum conditions (like small amounts of plug foulilng).