A year ago I heard an experienced pilot and mechanic talk about the nature of mag failures. How, due to the internal breakdown they end up firing impulses in no particular order or completely randomly, causing detonation, misfires, rough engines and failure. I remember thinking that I didn't know that mags could behave like that - I thought they either ran rough, not at all or good. I stored this information somewhere.
I'm glad I did.
After a two day long cross country to Chicago with the worst weather I've ever encountered (I'll write a trip post on that sometime in the future), tired, on the final leg into Chicago the left engine misfired briefly. It wasn't enough time to try to trouble shoot. Soon after that it came back worse and for much longer, and here I had time to try stuff. I tried the booster pumps, the power, the mixtures, the props etc. Didn't work. I was just about to call the center and declare my intentions of diverting swiftly when I remembered that mag story. I switched mag. Nothing. Then I tried again and it ran like butter! I had missed the detent on the first try.
I know this might be standard procedure for some, but I had never been taught that mags could fail like that,
overpowering the good mag. I'd also never been consistently taught to check mags in an emergency. I always thought I had two for redundancy, and when one fails the engine just keeps going on the second. Not so.
With the Iowa flatlands below me and airports every 2 miles it wasn't going to kill me here, but this could have been life saving information any other place - especially since my left engine is the only one with the hydraulic pump on it which means if it fails the gear comes down weather you like it or not. In mountains and at high density altitudes, this could have been a killer.
So if the engines starts to abruptly misfire and run rough, check the mags first thing!
