What is a Magneto? You check both the left and the right one each time you complete your pre-flight checks – but do you know what they are?
A magneto is so named as it is comprised of a permanent magnet which creates a voltage high enough to create a spark. This is used to ignite the fuel within the cylinder of the aircraft’s engine.
Most cars use an ignition system that relies on an alternator, which in turn powers a battery. If the alternator fails, the battery is no longer charged and it will eventually stop supplying current to the ignition system and the engine will grind to a halt. Not great if you are between aerodromes at 200ft asl…
It is widely considered safer for an aircraft engine not to rely on a battery and therefore a magento system is used. In theory, if the battery fails, the motor will continue to run. As the engine crankshaft turns, the magnetos recharge, ready to fire the next spark.
EXAM TIP – The magnetos generate power independently of the aircraft electrical system for safety (Aircraft Technical Exam)
So why Two Magneto’s? And why a drop in engine power when you test?
Each cylinder has a separate lead from each magento, so if one magento fails the engine will still run. Each magneto fires on every other crankshaft rotation in turn. Therefore, if you test only the left magneto system the spark plug will fire only once in every two revolutions – slowing the engine slightly. It is just as important to witness an increase in power when you finish testing each magneto, ensuring both are working correctly – it could mean the difference between life and death!