Mag check on shutdown

[Colonel Sanders]

He won't talk about it - surprise - but I'm pretty
sure he accidentally turned both magnetos OFF
in flight, and instead of pulling the throttle back
to idle - panicked and turned the mags back on
again.

Problem is, while the mags are off, the engine
is pumping loads of unburned combustible gas/air
through the engine into the exhaust, and when
the mags go back on again, it lights off the gasoline
in the exhaust and can blow them right off the
airplane.

And, it did. In addition, the explosion was so
severe, it structurally damaged the skin of the
aircraft, and no one in Canada knew how to fix
it, so it was down for months. During that time,
the cam & lifters likely sustained serious corrosion.

Good job!

I'm sure you don't want to know what I would
do, if I was messing with the mags and the prop
started to windmill - I am sure I would get lots of
hate mail if I dared discuss it - but I would take
action to ensure that the gasoline was purged from
the exhaust before I put the mags back on again.

I think I can safely say that without people banning
me from the site, or dropping dimes to Enforcement.
You know, the usual.

Note that if you have a dead mag, merely selecting
L or R in flight can cause combustion to cease.

[pelmet]

if I was messing with the mags and the prop
started to windmill I would take
action to ensure that the gasoline was purged from
the exhaust before I put the mags back on again.

Note that if you have a dead mag, merely selecting
L or R in flight can cause combustion to cease.

So would just closing the throttle prior to selecting mags on again be sufficient?

[Colonel Sanders]

Closing the throttle is a step in the right
direction, but at the risk of being attacked
here yet again, I would do a little bit more
than that.

Listen to the afterfiring in this video:

http://www.youtube.com/watch?v=dHE503Rz ... lpage#t=24

I have the throttle all the way closed, with
the prop windmilling in a power-off descent
during the continuous base to final, yet plenty
of gasoline is still making it's way into the
engine, and you can hear it burning out the
exhaust.


Hint: you might perform a flooded start
procedure on the ground, if you suspected
there was too much gas in the engine and
you wanted to get rid of it, when you cranked
the engine.

How would you position the engine controls
for a flooded start?

[Beefitarian]

Mixture idle cutoff.

Edit: ok I got it now. the thing is flooded. I was thinking you accidently turned off the mags letting the fuel build up. I suppose they are similar.
I also was mixing in a carburetor fire instead of an exhaust fire.
In all three cases I want to stop introducing fuel and therefore stop feeding the fire.

I'll make the wrong part red now, it was a bad choice since the float bowl is still going to have fuel in it.

Throttle full. It should just be allowing air to go through the engine to help evaporate any excess fuel. since the mixture control in the cutoff position should be stopping more fuel from being introduced.

Let's go with, Throttle closed.

Might not hurt to check primer in and locked just in case even though I checked it many times during my lengthy checklist.

[Colonel Sanders]

I didn't say that. You did.

[Beefitarian]

Yes. If something there is wrong I'd delete/edit that post after a brief corrective explanation. I'm confident enough to do what I wrote at this time but...

[New_PIC]

Please forgive my lack of imagination, or caffeine, this morning CS but I don't see what would be contentious about the procedure that you're very carefully not advocating here. Could someone explain what the potential problem would be?

[Beefitarian]

Now I feel bad. Let's hope no one read that red part and blew up a muffler this morning.

[pelmet]

Closing the throttle is a step in the right
direction, but at the risk of being attacked
here yet again, I would do a little bit more
than that.

Listen to the afterfiring in this video:

http://www.youtube.com/watch?v=dHE503Rz ... lpage#t=24

I have the throttle all the way closed, with
the prop windmilling in a power-off descent
during the continuous base to final, yet plenty
of gasoline is still making it's way into the
engine, and you can hear it burning out the
exhaust.


Hint: you might perform a flooded start
procedure on the ground, if you suspected
there was too much gas in the engine and
you wanted to get rid of it, when you cranked
the engine.

How would you position the engine controls
for a flooded start?

Theoretical scenario: So my engine is running a bit rough and I want to check the mags. I select a single mag operation and the engine dies. No big deal, I have lots of altitude. I close the throttle and then put the mixture to idle cutoff, select mags to the other one(or back to both), then mixture rich, then open the throttle and the engine smoothly comes back. And all this happened because I thought about what to do prior to the mag check so that I didn't just instinctively flip the mag switch back to on after the engine died. Would the Colonel be all smiles for this procedure(despite his worry about being mercilessly attacked)?

[Big Pistons Forever]

Closing the throttle is a step in the right
direction, but at the risk of being attacked
here yet again, I would do a little bit more
than that.

Listen to the afterfiring in this video:

http://www.youtube.com/watch?v=dHE503Rz ... lpage#t=24

I have the throttle all the way closed, with
the prop windmilling in a power-off descent
during the continuous base to final, yet plenty
of gasoline is still making it's way into the
engine, and you can hear it burning out the
exhaust.


Hint: you might perform a flooded start
procedure on the ground, if you suspected
there was too much gas in the engine and
you wanted to get rid of it, when you cranked
the engine.

How would you position the engine controls
for a flooded start?

Theoretical scenario: So my engine is running a bit rough and I want to check the mags. I select a single mag operation and the engine dies. No big deal, I have lots of altitude. I close the throttle and then put the mixture to idle cutoff, select mags to the other one(or back to both), then mixture rich, then open the throttle and the engine smoothly comes back. And all this happened because I thought about what to do prior to the mag check so that I didn't just instinctively flip the mag switch back to on after the engine died. Would the Colonel be all smiles for this procedure(despite his worry about being mercilessly attacked)?

You don't have to even do that. Just immediately retard the throttle to idle and switch the mag(s) back on.

[Beefitarian]

Wee, a day later I'm going to continue to over think this one.

If you close the throttle it will likely draw that fuel from the float bowl even though you pulled the mixture cut off. As long as compression is good with the butterfly valve closed it should suck fuel out of the venturi. If I opened the throttle it would too. I would close the throttle before turning that mag back on, to reduce the flame entering the exhaust via fuel that would not be combusted normally.

If the fuel from the float bowl was run through while mixture was cut off. Throttle opened would be good during the windmilling without combustion since the extra air would cause a lean condition and exhaust that fuel mixture helping it evaporate quicker.

Hopefully if the closed throttle draws in more fuel it will cause an over rich condition with butterfly valve closed.

The worst would be to go to full rich mixture and opened throttle. Most low timers are probably coached to do so. In the end that might be best.

KISS, get that engine running while you soil yourself. Blowing up the muffler is bad, but hitting the fence because you never figured out how to get the engine going again might be worse.

Opinions, discussion?

[pelmet]

Wee, a day later I'm going to continue to over think this one.

If you close the throttle it will likely draw that fuel from the float bowl even though you pulled the mixture cut off. As long as compression is good with the butterfly valve closed it should suck fuel out of the venturi. If I opened the throttle it would too. I would close the throttle before turning that mag back on, to reduce the flame entering the exhaust via fuel that would not be combusted normally.

If the fuel from the float bowl was run through while mixture was cut off. Throttle opened would be good during the windmilling without combustion since the extra air would cause a lean condition and exhaust that fuel mixture helping it evaporate quicker.

Hopefully if the closed throttle draws in more fuel it will cause an over rich condition with butterfly valve closed.

The worst would be to go to full rich mixture and opened throttle. Most low timers are probably coached to do so. In the end that might be best.

KISS, get that engine running while you soil yourself. Blowing up the muffler is bad, but hitting the fence because you never figured out how to get the engine going again might be worse.

Opinions, discussion?

Opinion...almost everybody knows how to get the engine going again. But if there is a simple extra thing that can be done to prevent potential damage and can be thought out in advance of adjusting the mag switches, it would be good to spread the word.

[Beefitarian]

I'm thinking if I were actually flying. The engine is running rough enough and I'm far from a suitable place to pull in for an AME to take a look. If I select a magneto to isolate it. Then the engine quits I'm not going to count 15 bananas before re-selecting both.

Then I might select the other quickly to see if it runs better than both.

I do a "muffler death defying" mags off check on shut down as per checklist and have never got a bang. So... My opinion is if you are going to mess with the switch you should have pulled the throttle to idle first and possibly more importantly, get on it.
It's no time to be dilly dallying around.

[ruddersup?]

Hey Beef, I think you've it, lol. Don't dilly dally around. Left, right both = 1/2 second