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For more than 40 years, I have been hearing that piston airplanes use mags because they keep on ticking no matter what (unlike the other options that, under certain unlikely circumstances, could fail.) Specifically, a complete electrical failure, including any available backups, would make things get real quiet unless there was a mag or two on board. That's fine as far as it goes but it ignores a number of unfortunate facts such as:
Mags have multiple moving parts that wear over time.
Mags tend to arc at altitude, accelerating wear.
Mags (at least the ones I have been using) are built by Unison.
When I first flew my Legacy, I put in LASAR mags. They never worked right (i.e. never performed better with the LASAR system on than with it off.) In the process of trying to figure out why, after about 300 hrs, I pulled both mags and sent them in to Unison. Their inspection revealed that both were shot (nothing to do with LASAR, they were just shot) so they threw them out and invited me to buy two more at a small discount. I did but they worked no better so I finally talked Unison into exchanging the whole LASAR system for two ordinary mags. Those went on about 200 hrs. ago and, on the way to OSH this year, one of them failed in flight. I had that one replaced (at my expense) and had the other inspected. The inspection revealed a number of worn parts (making me feel real good about surviving the failure of the other one) which were replaced. So that's seven mags (plus some parts) in just over 500 hrs., all but two paid for by YT and one 60 mile course reversal in complete reliance on what was left of one remaining functioning mag.
But wait --- there's more!
My partner in the failed mag adventure just brought to my attention a mandatory service bulletin issued by Unison the general point of which is that the carbon brush is wearing prematurely in the field. A decent company might offer to replace the brushes (or whatever is causing them to wear prematurely) but not Unison. What they have come up with is that any mags that are recently installed or in which certain parts have recently been installed, have to be inspected after five hours and then twice or three times more in the next 50 (depending on how much time was on them when the five hour inspection was made.) Since the bulletin applies to both my mags (one because it is new and the other because of the new parts) that means pulling, inspecting, reinstalling and retiming both mags every couple weeks or so for a while. Since those are things I don't do myself (having no particular death wish) the cost is likely to be considerable, to say nothing of the annoyance.
And finally (except for the Ginsu kinves):
Apparently a friend of mine got one of these bad brush jobs in a brand new mag that he installed in his RV-10. The brush did not take long to fail. In fact, it began failing on climbout on his first flight, making the whole experience even more memorable than it would otherwise have been. In subsequent runups, it got worse and worse so they just shut down and pulled the mag.
Here's the good news: Unison is happy to replace the bad mag.
Here's the bad news: The process they have for doing so is more complex than the tax code and takes an average of eight weeks. (As Dave Barry would say, I swear I am not making this up.)
Needless to say, my friend is now several hundred dollars poorer but is flying his airplane.
Since I have been flying my airplane, I have had to replace:
the electric fuel pump once;
the vacuum pump once; and
mags five times.
The mags are by orders of magnitude the least reliable component in my airplane. Don't take my word for it -- just take a look at Unison Service Bulletin SB3-08. It's pretty obvious from that how much faith Unison has in them.
As soon as the 6-cylinder P-MAG is available, I am going to get a reliable ignition system.
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