14 C.F.R. § 33.37 Ignition system.
Title 14 - Aeronautics and Space
Each spark ignition engine must have a dual ignition system with at least two spark plugs for each cylinder and two separate electric circuits with separate sources of electrical energy, or have an ignition system of equivalent in-flight reliability.
Title 14: Aeronautics and Space
PART 33—AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES
Subpart C—Design and Construction; Reciprocating Aircraft Engines
§ 33.37 Ignition system.
