Training and Safety Tip: Spark check
Early on in flight training, you’ve learned to do a “mag check” as part of the aircraft engine runup.
That ritual of moving the key, first to L(eft), then back to Both, then to R(ight), then back to Both, all while watching the tachometer needle for a subtle drop. Hopefully, your flight instructor taught you the purpose of this check, but just in case: The airplane has two independent magnetos under the cowl, each providing electricity to one of the two spark plugs in every cylinder of your aircraft’s engine. If one of these magnetos fails, the other keeps the engine running—granted, on half the spark plugs. Still, that’s nice redundancy to have when flying over shark-infested waters, alligator-infested swamps, and other assorted inhospitable terrain.
Why perform a postflight check? Well, in many airplanes, the drop in engine performance if one magneto kicks the bucket in flight is subtle and can go unnoticed. Of course, you’d discover the problem before the next flight, but wouldn’t it be nicer to discover the issue earlier, and get it addressed before it fouls a flight?
Worse yet, in some older designs, magnetos can temporarily fail when hot. They may pass a startup cold check then fail in flight. You could be conducting multiple flights on a single magneto and be unaware. And should the remaining magneto then fail in flight over an alligator farm, your day may end badly.
There’s nothing wrong with an in-flight mag check, either, particularly if you’re heading toward water, wilderness, or approaching a large alligator farm. (Although your heart will skip a beat if you do discover a dead magneto in flight.)
In-flight checks have the added benefit of increasing your experience and confidence in systems troubleshooting and can prepare you for dealing with the most dangerous kind of magneto failure: one where instead of simply failing to fire, a magneto fires at the wrong time, wreaking havoc on the engine. If this happens, a quick in-flight mag check can isolate the problem. Just use that simple magneto key switch by turning it from Both to the Left and Right positions to identify and isolate the bad magneto. Then, simply continue your flight on the good magneto to a safe—and shark-free—landing.
