Which malfunction would cause an aircraft reciprocating engine to continue to run after the ignition switch is placed in Off?

Which malfunction would cause an aircraft reciprocating engine to continue to run after the ignition switch is placed in Off?

• A. Ignition switch is not grounding the magneto primary circuit.
• B. Battery is disconnected
• C. Alternator failure
• D. Starter motor engaged

Answer: (A)

The engine keeps running because the spark is still being produced even with the ignition switch in the Off position. In a reciprocating engine with magnetos, Off is supposed to ground the magneto primary circuit so no spark is generated. If the ignition switch fails to ground that circuit, the magnetos remain energized and continue to fire, letting the engine keep running despite being “Off.” Other issues like a disconnected battery, an alternator failure, or the starter motor being engaged don’t directly stop the magnetos from producing spark, since magnetos operate independently of the battery and alternator while the engine is running. The specific failure described—no grounding of the magneto primary circuit—explains why the engine would continue to run when the switch is Off.

The engine keeps running because the spark is still being produced even with the ignition switch in the Off position. In a reciprocating engine with magnetos, Off is supposed to ground the magneto primary circuit so no spark is generated. If the ignition switch fails to ground that circuit, the magnetos remain energized and continue to fire, letting the engine keep running despite being “Off.”

Other issues like a disconnected battery, an alternator failure, or the starter motor being engaged don’t directly stop the magnetos from producing spark, since magnetos operate independently of the battery and alternator while the engine is running. The specific failure described—no grounding of the magneto primary circuit—explains why the engine would continue to run when the switch is Off.