Here is the hypothetical scenario. Mag check 250 rpm drop on right mag, left fine. Try 3 times to burn it clean, no go.

What do you do?

A: Fly anyway
B: Pull the plug
C: Fly for 5-10 minutes land and do another mag check

Can you do a mag check in flight at any RPM?

Inquiring minds want to know.

Rob

Pull all the plugs clean and rotate them.

Then change your plug service/operation habits.

More data would be nice, like EGT's if you have individual readouts. This would tell you if it's just one plug fowled, or if it's a pending problem with a mag. Could be as bad as a loose mag hold down that's allowed the mag to shift a bit. Having a mag come loose in flight can be a really bad thing.

Fowled plug, bad ignition lead, or mag, I'd be inclined to fix it before flying if I had the tools or resources available.

You can do a mag check in flight. However, if you switch both mags off, or one is completely crapped out and you select that one, be quick about switching back to the good one or both. Otherwise raw fuel will get into the exhaust system and when you do get the fire lit again, it can backfire go boom and potentially damage things.

Once upon a long time ago, I heard of a pilot who had a mag fail completely (cracked coil) on an Aeronca 7AC. This happeded at an out of the way location with some 60 miles of enemy territory between there and home. Our hapless pilot flew it safely home on one mag, but the stress and sweating weren't worth it.

bumper

RobBurson wrote:Can you do a mag check in flight at any RPM?

Inquiring minds want to know.

Rob

Yes. The only way to really know if your ignition is up to par is a mag check at cruise power. Also specifically recommended by the engine gurus like John Deakin. See his articles on Avweb.

Getting a clean mag check on my Maule with an O540 has been a problem since day one. Everything was checked OH mag, new wires, etc. That all helped and at least eliminated what was not the problem.

The best change was to 12 Iridium fine wire plugs. That cured most of it, but I still get a dirty mag check occasionally.
I now know that the drop during mag check is probably a fouled plug. But the Iridium plugs will burn off during takeoff everytime. So, as recommended by many who fly on dirt or gravel, I do a rolling mag check, if it is safe to do so, if not or I forget, I do an inflight mag check shortly after takeoff, with the field in site.

I have been at short strips in a canyon where I was not comfortable with any loss of power, so I pulled plugs in the field and could easily see the lead fouling and was able to correct it.

Hey Rob, When you say you "Try 3 times to burn it clean" does that mean you are leaning the mixture at engine check RPM? That is what I do and it usually works well.

Skystrider wrote:Hey Rob, When you say you "Try 3 times to burn it clean" does that mean you are leaning the mixture at engine check RPM? That is what I do and it usually works well.

I'm not admitting to anything. When I have a problem like the hypothetical here. I lean while burning the lead out. Works fine. Most of the time I run 87 UL mogas without ethanol. You do not foul plugs on that.

I like your idea Mr Scout. I always try to keep the rpm at or above 1100 to keep from lead fouling but on long taxi's or strong tail winds it gets the brakes to hot.

Guys, thanks for the info.

Rob

So what's the best technique for physically cleaning plugs? I've never cleaned aircraft spark plugs, only on my dirt bikes, and I used a fine wire brush.

Depends on the engine involved and how the mags are wired to which plugs.....one mag to the top plugs, one mag to the bottom plugs, or each mag wired to both top and bottom plugs?
If the mag drop is consistantly the mag for the bottom plugs and lead fouling is a constant problem try a little Marvel Mystery oil (4oz/10gal 100LL) mixed in the fuel. I found this really helps on a Continental engine (C-145).
Yes sometimes a fouled plug may come clean by "burning" it but it could also be shuch a thing as a broken ring, bad valve guide, or even a faulty plug ( is it lead or black carbon fouling). A park plug may yest OK at atomaspheric pressure but may not fire under compression.
Also a bad spark plug wire could cause the plug to not get a hot enough spark. We always check the timing, mag output, and the insulation of the wires at every annual.
Also when in question and all of the above provide no results, pull the mags and check for cracks, oil integration, coil failure, condenser failure, and cracked or broken gears etc.
One more thing...if different RPM's produce different drops in RPM, look for an induction leak in the intake manifold or carburation system.
This is especially true at lower RPM's..air/fuel mixture is not consistant for all cylinders ( have seen this happen in several small Continental engines).
HC

Found myself in a similar situation a couple of weeks ago. Mag check revealed a significant drop on the left mag and had to fly home on the right only. Didn't have anything with me to pull the plugs and attempts to 'burn off' assumed fouled plugs didn't work. Another pilot stopped to help but couldn't identify the problem either.
Needless to say, I used up the entire runway getting out and had one of those memorable flights home with minimal power. Didn't help that my Franklin has a limitation preventing operation between 2100 and 2300.

Turns out an internal bushing? on my mag failed and I couldn't have resolved the problem myself but it did cause me to up the inventory of tools that I take with me.

Try following Lycoming's recommendations on how to shutdown your engine---that will probably reduce the likelyhood of fouled plugs at least.

Take a look at Lycoming's web site, and search for Lycomings Reprints

MTV

Since we can't get TCP any more I started using Marvel Mystery oil.... I haven't had a bad run up since I started. I usually have a rough running engine on one mag before I started using Marvel but it has since gone away. I have the IO 360 Cont. Great stuff that.....

Get in touch with your friendly local A & P mechanic, and have him/her SHOW you how to PROPERLY clean a spark plug.

This process is perfectly legal for a non A & P to do, but learn how to do it correctly from a mechanic first. There are a lot of little issues involved and it's best in my opinion to learn first hand.

MTV

RobBurson wrote:Here is the hypothetical scenario. Mag check 250 rpm drop on right mag, left fine. Try 3 times to burn it clean, no go.

What do you do?

A: Fly anyway
B: Pull the plug
C: Fly for 5-10 minutes land and do another mag check

Can you do a mag check in flight at any RPM?

Inquiring minds want to know.

Rob

Flight:
Finding dead plug is easy - Open cowl ,gain access to exhaust > get crayon or grease pencil. Run engine on rough mag for short runup be careful here watch out prop or shut down. Mark on exhaust risers near cylinders and watch which ones that mark or melt. those that melt indicates cylinder that is burning>working . Those that "mark" is cold cylinder is one to pull the plugs and clean. I carry 2 extra plugs and tools in my 182 to fix it wherever .

mtv wrote:Try following Lycoming's recommendations on how to shutdown your engine---that will probably reduce the likelyhood of fouled plugs at least.

Take a look at Lycoming's web site, and search for Lycomings Reprints

MTV

9. Prior to engine shutdown, the engine speed should be maintained
between 1000 and 1200 RPM until the operating temperatures
have stabilized. At this time, the engine speed should be increased to approximately 1800 RPM for 15 to 20 seconds, then reduced to 1000 to 1200 RPM and shut down immediately using the mixture control.”

I've never run mine all the way up to 1800, but I do run it to 1500 everytime I shut it down.