There I was…

Elbow deep in the floor structure of the Embraer when I hear the following ominous statement:

“There’s something wrong with the Lance.”  

The Lance is one of our (my) little bugmashers; built by Piper and usually solid as a rock.  It had just taxied out to fly a load of concrete to Lake Minchumina, about 150 miles southwest of Fairbanks.  One of the checks Joe Pilot does before take-off is called a mag drop check.  Piston driven airplanes have two magnetos that provide the high voltage to the spark plugs; one for each set of plugs.  There are two spark plugs in each cylinder in case one of the plugs, wires, or magnetos fails in flight.  The other plug will keep firing the cylinder and the engine keeps running. What happened this time was there was too much of an RPM loss when the engine was checked with only one magneto powering the spark plugs. 

Easy fix usually.  I run out into the brisk 10 degree ( above 0 at least!) air and pull the top cowling half off the engine.  Nothing obvious wrong so I yank out all 12 plugs and bring them inside for a run through the plug checker.  I start at the #6 cylinder bottom plug and run through them in order towards the # 1 top plug.  Nothing.  Nada.  Zippo.  Until I get to the #1 bottom plug.  There’s a really weak, tiny little spark at the very edge of the electrode; nowhere near enough to fire the cylinder on its own.

Replace the bad actor with a new plug, reinstall them all back into the engine, cowl it up, and run the beast till it gets warm again.  One quick mag drop check later and I’m pulling up to the Operations door with a fixed bugmasher and seriously cold fingertips.


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