The ignition requirements are pretty straight-forward:
§23.1165 Engine ignition systems.
(a) Each battery ignition system must be supplemented by a generator
that is automatically available as an alternate source of electrical
energy to allow continued engine operation if any battery becomes
(b) The capacity of batteries and generators must be large enough to
meet the simultaneous demands of the engine ignition system and the
greatest demands of any electrical system components that draw from
the same source.
(c) The design of the engine ignition system must account for—
(1) The condition of an inoperative generator;
(2) The condition of a completely depleted battery with the generator
running at its normal operating speed; and
(3) The condition of a completely depleted battery with the generator
operating at idling speed, if there is only one battery.
(d) There must be means to warn appropriate crewmembers if
malfunctioning of any part of the electrical system is causing the
continuous discharge of any battery used for engine ignition.
(e) Each turbine engine ignition system must be independent of any
electrical circuit that is not used for assisting, controlling, or
analyzing the operation of that system.
(f) In addition, for commuter category airplanes, each turbine engine
ignition system must be an essential electrical load.