Shutting down

flyingcheesehead

flyingcheesehead

Touchdown! Greaser!
Joined
Feb 23, 2005
Messages
24,899
Location
UQACY, WI
Display Name
Display name:
iMooniac
Sigh... I'm old enough that I've forgotten some of the things I learned 10-20 years ago...

For a LONG time, I have been shutting down piston aircraft engines in the order Mixture -> Alternator -> Mags -> Master.

I had a reason for doing that, based on some posts here ages ago. However, now that I'm looking through all of my procedures and making myself justify them... I don't remember any of why I do it that way, nor do I even remember who posted the things I had based that off of. And my POH says Mixture -> Alternator -> Master -> Mags.

What would be the mechanical/electrical reasons behind the order of operations for shutdown?
 
My shutdown sequence is the opposite of startup:
1. Alternator field. Aside from ensuring that the ALT INOP light works, I am ambivalent on the necessity/usefulness of this step.
2. Master. Why? Because if I do this now, I'm less likely to forget it later.
3. Mixture ICO.
4. Mags off.
5. Fuel selector off.
 
flyingcheesehead said:
Sigh... I'm old enough that I've forgotten some of the things I learned 10-20 years ago...

For a LONG time, I have been shutting down piston aircraft engines in the order Mixture -> Alternator -> Mags -> Master.

I had a reason for doing that, based on some posts here ages ago. However, now that I'm looking through all of my procedures and making myself justify them... I don't remember any of why I do it that way, nor do I even remember who posted the things I had based that off of. And my POH says Mixture -> Alternator -> Master -> Mags.

What would be the mechanical/electrical reasons behind the order of operations for shutdown?
Click to expand...
Mixture before mags is kinda important.
 
Clip4 said:
Mixture before mags is kinda important.
Click to expand...
Anything other than the obvious "don't leave a burnable mixture in the cylinders after shutdown"?

Not really what I'm looking for anyway, it's mostly the other things, but what the hey, might as well learn everything I can.
 
flyingcheesehead said:
Anything other than the obvious "don't leave a burnable mixture in the cylinders after shutdown"?

Not really what I'm looking for anyway, it's mostly the other things, but what the hey, might as well learn everything I can.
Click to expand...
I've seen some checklists that recommend mags to off briefly then back to both prior to mixture ICO.

This verifies P-Lead grounding and ignition switch functionality.
 
flyingcheesehead said:
Anything other than the obvious "don't leave a burnable mixture in the cylinders after shutdown"?

Not really what I'm looking for anyway, it's mostly the other things, but what the hey, might as well learn everything I can.
Click to expand...
That's the reason. You don't leave fuel in the engine.

I was always taught to shut off all electrical before shutting down the engine, maybe something about a surge. I think this is more likely on startup though.

I shut off radios, master & alternator, mixture, then mags.
 
flyingcheesehead said:
Anything other than the obvious "don't leave a burnable mixture in the cylinders after shutdown"?

Not really what I'm looking for anyway, it's mostly the other things, but what the hey, might as well learn everything I can.
Click to expand...
You don’t want to leave fuel in the exhaust either.
 
Master last because you want the beacon to be on while the mags are hot?

Also, avionics is last on and first off because you want the voltage to be stable.
 
Here's my process:
Avionics master off, because that stuff is expensive.
Alternator off (might make the first step redundant) to prevent any voltage spikes during shutdown, and excessive field current.
Mag checks, sometimes.
Mixture to idle cutoff.
Battery off.

On start-up, I always start with the alternator off, less load on the engine and the battery, less of a chance of things getting damaged due to electrical spikes.
 
I just go right to left:

Avionics master off
Mixture to cutoff
Master and Alternator off (split switch, I just shut off both at the same time)
Mags off

Verify G5s shut down (otherwise they drain the backup batteries)
 
So... Lots of good points, but the main thing I'm looking for is just the last part - Mags, then Master, or Master, then Mags? And presumably it's best to have the mags on until the engine stops spinning...

Maybe that's all I'm vaguely remembering is to not shut off mags before the engine is done turning?
 
I don't think it really matters.
My logic says mags, then master, because it allows me to complete my shutdown checks (which may include checking engine instruments, writing down times/fuel remaining) while having a secured engine. And I can have lights on in the plane while doing that at night.
 
flyingcheesehead said:
Sigh... I'm old enough that I've forgotten some of the things I learned 10-20 years ago...

For a LONG time, I have been shutting down piston aircraft engines in the order Mixture -> Alternator -> Mags -> Master.

I had a reason for doing that, based on some posts here ages ago. However, now that I'm looking through all of my procedures and making myself justify them... I don't remember any of why I do it that way, nor do I even remember who posted the things I had based that off of. And my POH says Mixture -> Alternator -> Master -> Mags.

What would be the mechanical/electrical reasons behind the order of operations for shutdown?
Click to expand...
To add what others have said, I don't think the order of the last to things matter at all, in part because in most aircraft the mags aren't connected to the DC electrical system. The exception that comes to mind being something with electronic ignition.

And that said, first plane I learned on was always to turn off via mags. Partly because there was no mixture control, and partly because it's kinda nice to verify that the mag switch actually will shut off the engine, if next time you start it you're going to hand prop it.

And I always shut off the avionics first, if there's a switch for that, to reduce the chance of them getting a spike on shutdown. I leave the master on until after shutdown, on the possibly mistaken belief that having the battery and alternator connected is a good plan to reduce chances of damage to the alternator/regulator on either shutdown or startup. Oh yeah, and because it's in the POH that way.
 
I toasted a transponder years ago when the engine stalled on taxi-out with everything on. C182
I reached down without doing anything else and cranked, restarted, heard a pop and no transponder after that moment.
So I see it as a practicality, not just a theory, that I should bring electronics on and offline, separate from engine starts and stops.
Yes, n=1 but it was an undeniable association in my mind.
 
Let'sgoflying! said:
I toasted a transponder years ago when the engine stalled on taxi-out with everything on. C182
I reached down without doing anything else and cranked, restarted, heard a pop and no transponder after that moment.
So I see it as a practicality, not just a theory, that I should bring electronics on and offline, separate from engine starts and stops.
Yes, n=1 but it was an undeniable association in my mind.
Click to expand...
The 182-S POH certainly agrees with you. I follow it....Avio-Mix-Mags-Mast
 
I use the acronym REMM,M which mirrors a number of factory checklists.

Radios
Electrical Switches
Mixture
Master
, Wait for engine to stop turning
Mags

Brian
 
You must log in or register to reply here.
Back
Top