Now envision a failed starting
attempt. The ship doesn't light so the pilot lets go of the
starter switch. However, as the engine winds down to
zero rpm, the
permanent magnets in the starter (if so improperly equipped)
may both keep the starter engaged to the ring gear as well as
power the shower of sparks system. Should it
generate a spark ahead of TDC, conditions are ripe for a nasty
kickback.
That's why only field-wound starters
are recommended for all helicopter applications (Sky-Tec HT or NL models for Lycoming-powered rotorcraft)
