My experience with failed mags is fortunately limited to Fouled plugs
on the runup. However I am aware of 2 interesting incidents involving
Mag's.

1. My flight Instructor was flying departing in a 414. Upon starting
one engine he could just barely get it run it was coughing, sputtering
backfiring, etc. He shut down and brought the Mechanic who determined
that the timing on one of the Mags had slipped. It was firing but at
the wrong time. Sorry I am not a Mechanic so I don't know what would
have happed to cause that. However had my instuctor done a mag check
he would have found that the engine ran fine on one mag and not at all
on the other. lesson Learned if an engine start running rough or badly
in flight a mag check is a worth while check.

2. A local Cropduster pilot had just finished up and was taking his
Ag-Cat back to the home base about 5 miles away. On his Runup he
discovered that one mag had died completely. He opted to fly it back
to base to get it fixed. Upon landing at his home base he 1st took it
to the fuel pump and fueled it. After Fueling he could not get it to
start. The 2nd Mag had failed!

So far my worse experience with a Mechanical Fail has been the nut on
one of the intake valves worked loose in our Tomahawk and the engine
began running rough and lost a couple hundred RPM. We simply informed
ATC that the engine was running rough and we were diverting to the
nearest airport.

Brian
CFIIG/ASEL