Alfa Romeo have often employed dual ignition since the 60s for a leaner burn and higher power. Igniting the mixture at two different points caused a quicker burn and allowed tighter timings.
Don't know anything about this regarding fighter a/c, though. Presumably if dual ignition was used to tighten timings, knock would become a serious issue if one circuit was knocked out. OTOH, a dual system would provide redundancy but only a tiny increase in power if the ignition timing was the same as a single-ignition setup.
dduff
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