Piston shutdown procedures

spinfire

spinfire

Pre-takeoff checklist
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Dan
An instructor once taught me the following technique for my IO-360:

  1. Avionics/switches off
  2. Set throttle to 1200 RPM idle
  3. Slowly lean by twisting the mixture knob until the engine begins to die
  4. At the first sign of the engine roughening due to the lean mixture pull the mixture knob out all the way
  5. When the prop is almost stopped, pull the throttle all the way closed
  6. Finally, as always, mags and master go off

There are some differences with what was originally taught to me in a carb'd 172. There, I just set around 1000 rpm idle, pulled the mixture all the way out (that plane didn't even have a vernier), and let the prop rattle to a stop.

Notably, the final step of pulling the throttle closed is intended to avoid the rough jerky shudder of those final compression strokes. It seems to work quite well and the engine shuts down smoothly without the typical death shudder. My IO-360 shudders much more on shutdown without this step than the O320 in the 172K I learned in but I suspect that has to do with the larger displacement and compression ratio.

I'd like to verify that I am not doing anything bad to the engine by taking this extra step since most discussions don't mention it. If anything it seems to reduce the vibrations experienced which strikes me as a good thing. Thanks.
 
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or just throttle to idle then mixture all the way back. Your instructor has fixated in irrelevant things while leaving out the only important thing. After the engine stops, turn off the mags.
 
My instructor did not leave out the discussion of switches, mags, and master. I did, because I assume we all know those steps of the shutdown procedure and I didn't think they were relevant to my question. In the 172, I learned "switches, lean, ignition, master" mnemonic. I updated my original post to eliminate any confusion.

It sounds like you actually pull the throttle all the way to idle before pulling the mixture back. The idea behind doing the slow lean at 1200 rpm is to keep the plugs as clean as possible. During my first annual the IA did comment the plugs were extremely clean and I have never had a problem with plug fouling so there may be some truth to that.
 
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spinfire said:
It sounds like you actually pull the throttle all the way to idle before pulling the mixture back. The idea behind doing the slow lean at 1200 rpm is to keep the plugs as clean as possible. During my first annual the IA did comment the plugs were extremely clean and I have never had a problem with plug fouling so there may be some truth to that.
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insignificant. You did your plug fouling, if any, on landing and
taxi in. Just my opinion, but there is no need to idle an engine one second longer than necessary in a hangar environment that might include children and dogs. I pull both mixtures with throttles at idle while still a couple hangars down from mine. It will coast.
 
I lean my mixture (o-360) when I leave the runway and do my clean up. my plane is bad about fouling if mixture is not leaned during taxi.
 
JHW said:
insignificant. You did your plug fouling, if any, on landing and
taxi in. Just my opinion, but there is no need to idle an engine one second longer than necessary in a hangar environment that might include children and dogs. I pull both mixtures with throttles at idle while still a couple hangars down from mine. It will coast.
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I do the same thing. People think I'm nuts for coasting into a spot with the engine shut down. I think the line folks generally appreciate not getting chased down by a giant food processor.
 
I add an extra step. In the leaning process, don't go all the way to cut out and turn the mags off momentarily to see if the engine cuts out, then back on and kill it with the mixture. That way you know the mags are cold before you go pushing around the plane by the prop with a warm engine. Even with the mixture cut off, the bowl vent or vaporizing fuel in the injection is still pouring vapor into the induction system. Given enough time this can allow for a 'pop through' of a cylinder or two if you pull the prop through a compression stroke. A warm engine primed with vapor is very easy to hand start, sometimes I get surprised when doing it on purpose just how easy it fired.
 
Yes, I should note that this is all in addition to the usual "aggressive ground leaning" once I am off the runway and for all ground ops. I've actually never met a pilot who didn't lean aggressively on the ground but apparently they do exist because people are always mentioning this as advice.
 
Henning said:
I add an extra step. In the leaning process, don't go all the way to cut out and turn the mags off momentarily to see if the engine cuts out, then back on and kill it with the mixture. That way you know the mags are cold before you go pushing around the plane by the prop with a warm engine. Even with the mixture cut off, the bowl vent or vaporizing fuel in the injection is still pouring vapor into the induction system. Given enough time this can allow for a 'pop through' of a cylinder or two if you pull the prop through a compression stroke. A warm engine primed with vapor is very easy to hand start, sometimes I get surprised when doing it on purpose just how easy it fired.
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It seems that this is a poor test.

If you turn off the fire in an engine near kill point, you have fuel and air in the cylider but no ignition, you basically just doused the plugs; of course it should stop. Only reason it would continue to run is if it's dieselizing. In that case, you have another problem and it may not be ignition related.
 
Jaybird, I believe the idea is to detect a hot (malfunctioning) mag. If the p-lead does not ground properly then the mag will not shut down. At all. So if the engine *doesn't* stumble when you bring the mags offline then something is wrong.
 
spinfire said:
An instructor once taught me the following technique for my IO-360:

  1. Avionics/switches off
  2. Set throttle to 1200 RPM idle
  3. Slowly lean by twisting the mixture knob until the engine begins to die
  4. At the first sign of the engine roughening due to the lean mixture pull the mixture knob out all the way
  5. When the prop is almost stopped, pull the throttle all the way closed
  6. Finally, as always, mags and master go off
Click to expand...
I'm sitting in Lycoming engine school right now. The instructor convincingly explained that operating at engine speeds below 1,000 rpm will have a significant effect on lead deposits. And that while it may seem that whatever negative effects may come from momentary operation below 1,000 would come slowly and gradually, he specifically described how it happens quite quickly as combustion chamber temperatures drop. He confirmed that leaning, when possible, has positive effects.

Here is an excerpt from Lycoming Service Letter No. L185B
2. The engine should be operated at engine speeds between 1000 and 1200 RPM after starting and
during the initial warm-up period. Avoid prolonged closed throttle idle engine speed operation
(when possible). At engine speeds from 1000 to 1200 RPM, the spark plug core temperatures are
hot enough to activate the lead scavenging agents contained in the fuel which retards the formation
of the lead salt deposits on the spark plugs and exhaust valve stems. Avoid rapid engine speed
changes after start-up and use only the power settings required to taxi.
3. Rapid engine cool down from low power altitude changes, low power landing approach and/or
engine shut-down too soon after landing or ground runs should be avoided.
4. Prior to the engine shut-down, the engine speed should be maintained between 1000 and 1200 RPM
until the operating temperatures have stabilized. At this time the engine should be increased to
approximately 1800 RPM for 15 to 20 seconds, then reduced to 1000-1200 RPM and shut-down
immediately using the mixture control.​

I can't think of any reason not to follow the factory recommendation on this point.
 
Jaybird180 said:
It seems that this is a poor test.
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Its a good test to see if you mags are still grounding when the switch is off.

Jaybird180 said:
Only reason it would continue to run is if it's dieselizing.
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Wrong, if you have a broken P-Lead it will continue to run; hence the test.

Notice what he said:
In the leaning process, don't go all the way to cut out and turn the mags off momentarily to see if the engine cuts out, then back on
 
Jaybird180 said:
It seems that this is a poor test.

If you turn off the fire in an engine near kill point, you have fuel and air in the cylider but no ignition, you basically just doused the plugs; of course it should stop. Only reason it would continue to run is if it's dieselizing. In that case, you have another problem and it may not be ignition related.
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I'm not shutting off the engine with the mags, I'm shutting off the engine with the mixture. I momentarily hit the switches and listen for the engine to fall off. As soon as it falls off mags go back on, engine still running, then I pull the mixture. If you turn off the mags and the engine keeps running, you have a fault in a P-Lead or switch and have hot mags on the ramp.
 
Bill Watson said:
I can't think of any reason not to follow the factory recommendation on this point.
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I also work for an engine manufacturer. And we likewise recommend all sorts of things that are ideal for an engine on a test stand but are impractical, unwise, and/or unsafe in a vehicle in the real world. In your example, riding the brakes while taxiing with 1000+ rpm or blasting your hangar door at 1800rpm
 
Bill Watson said:
Here is an excerpt from Lycoming Service Letter No. L185B
(snip)

I can't think of any reason not to follow the factory recommendation on this point.
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Yes, this was the reasoning stated to me for keeping the ground ops between 1000 and 1200 RPM aggressively leaned and for shutting down with the mixture control with the engine idling around 1200 RPM. I follow those recommendations pretty much exactly and usually give a short higher burst of power before I pull into the aisle where my tie down is, just as described in the service letter.

The idea of pulling the throttle all the way out was the thing I hadn't heard discussed widely. Since it seems many people do shut their engines down while at the lowest possible idle with the throttle all the way closed (in contradiction to Lycoming's recommendation) it seems shutting the throttle completely once the mixture is pulled is a likely safe and effective way to eliminate the shutdown shudder.
 
spinfire said:
Jaybird, I believe the idea is to detect a hot (malfunctioning) mag. If the p-lead does not ground properly then the mag will not shut down. At all. So if the engine *doesn't* stumble when you bring the mags offline then something is wrong.
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In many aircraft it is actually a required AD to check.
 
Henning said:
I modify it for safety and liability reasons.
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Isn't the POH approved / controlled by the FAA? If so, one would assume the procedure is safe and the liability is not on you. OTOH, if you deviate from the approved procedure seems the liability is on you. :dunno:

OTOOH, if the POH isn't approved / controlled by the FAA, do what you think is best.;)

Cheers
 
X3 Skier said:
Isn't the POH approved / controlled by the FAA? If so, one would assume the procedure is safe and the liability is not on you. OTOH, if you deviate from the approved procedure seems the liability is on you. :dunno:

OTOOH, if the POH isn't approved / controlled by the FAA, do what you think is best.;)

Cheers
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If there is no mag check in the procedure it is not safe. It may be approved, but that does not make it safe nor absolve me of the liability of a plane on a ramp with a hot mag.
 
Muttley said:
Avionics off
Pull red knob
Mags off
Master off

Anything more complicated is just checklist masturbation and ultimately pointless
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Until the prop whips around and hits you as you push/pull the plane.
 
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Jaybird180 said:
It seems that this is a poor test.

If you turn off the fire in an engine near kill point, you have fuel and air in the cylider but no ignition, you basically just doused the plugs; of course it should stop. Only reason it would continue to run is if it's dieselizing. In that case, you have another problem and it may not be ignition related.
Click to expand...

Except it's not.
 
Bill Watson said:
...the engine should be increased to
approximately 1800 RPM for 15 to 20 seconds, then reduced to 1000-1200 RPM and shut-down
immediately using the mixture control.
Click to expand...

This is what is required by my club.
 
Muttley said:
Are you implying that the only thing keeping a prop from turning on its own is a properly connected P-lead? How many times has this happened to you or anyone you know?

It's a valid theory but practically irrelevant
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Not turning on it's own, firing when the prop is pulled through a compression stroke. Many people push and pull their plane by the prop, and often reposition it horizontally; although if on a ramp and it has a spinner you should position it vertically so puddles of water can't sit in the spinner, it can cause corrosion, and also lead to a chunk of ice in there which makes for an exciting start up.
 
I was taught the P-lead check as S.O.P. during my primary training. After parking, avionics off, then just a quick flick of the key to OFF and then back through L/R/BOTH, mixture lean, mags, master. Seemed like a prudent step considering I was about to grab a two-bladed killing machine a minute later.
 
dukeblue219 said:
I was taught the P-lead check as S.O.P. during my primary training. After parking, avionics off, then just a quick flick of the key to OFF and then back through L/R/BOTH, mixture lean, mags, master. Seemed like a prudent step considering I was about to grab a two-bladed killing machine a minute later.
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It really only takes a few seconds and can save your life, I never understood why so few people do it.
 
GCA319 said:
It really only takes a few seconds and can save your life, I never understood why so few people do it.
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...and something else to worry about and watch for: On the key switches found in many spam cans, there is a failure mode where if you turn the key switch to off and keep pressure on the key in a counterclockwise direction, the mags are grounded. If you release the key, the internal detent mechanism will move the key to the middle of the off position where one or more mags will be hot.

So a proper mag check at shutdown in one of those planes is key off, remove hand from key, (verify engine is spinning down) grab key, turn mags on, proceed with shutdown via the red knob.

I had one of those keys go bad on me a long time ago, and fortunately the engine did not fire when I tugged the plane into position for tiedown.

-Skip
 
Muttley said:
Are you implying that the only thing keeping a prop from turning on its own is a properly connected P-lead? How many times has this happened to you or anyone you know?

It's a valid theory but practically irrelevant
Click to expand...


About once a year or so I will flip the mags to off on a plane I am running or just flew and nothing will happen, the engine will keep on running. I've seen p-leads fall off, break, or just have too much resistance to function, as well as failed ignition switches or failed wires in the magneto. Magneto p-leads fail "safe" most of the time in that a failed lead will not shut down the engine. Safe in flight is quite unsafe on the ground when the prop stops vertical and you need to hook up the tow bar to push the plane back. The engine doesn't even have to start, just kick over to kill you. Another reason to always treat the prop like it could turn at any time, just like gun safety 101, "a gun is always loaded"


2 seconds of time could save a life. Show me a pilot who has/will never turn a prop by hand for any reason and I will show you a liar.
 
Skip Miller said:
...and something else to worry about and watch for: On the key switches found in many spam cans, there is a failure mode where if you turn the key switch to off and keep pressure on the key in a counterclockwise direction, the mags are grounded. If you release the key, the internal detent mechanism will move the key to the middle of the off position where one or more mags will be hot.

So a proper mag check at shutdown in one of those planes is key off, remove hand from key, (verify engine is spinning down) grab key, turn mags on, proceed with shutdown via the red knob.

I had one of those keys go bad on me a long time ago, and fortunately the engine did not fire when I tugged the plane into position for tiedown.

-Skip
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Another one that I see that I do not pass on inspection is a key that comes out in any on position. If they keys can come out while the mags are hot I don't want it in my hangar, I aim to die of old age before an airplane kills me.
 
JHW said:
I also work for an engine manufacturer. And we likewise recommend all sorts of things that are ideal for an engine on a test stand but are impractical, unwise, and/or unsafe in a vehicle in the real world. In your example, riding the brakes while taxiing with 1000+ rpm or blasting your hangar door at 1800rpm
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I don't work for anyone.

I agree tha practicality, wisdom and safety override any lead fouling issues.

However, I've been taxiing a Maule and now an Rv10 at 1,000rpms while leaned. It does require repeated taps on the brakes but I never considered that riding the brakes. I just did it because that's what the POH said (I believe) and everyone I trusted agreed.

For shut down I just pulled the mixture to kill it at 800 to 1000rpm. At home I have to go to 1500 or so to get up the hill and in the hangar. Recently with the '10, I've been try to eliminate the shudder by idling down then gently going to mixture cutoff. It's easy to do but it doesn't seem to be the optimal procedure. I just started getting It up to 1200 befor pulling the red knob, shudder be damned. I kind of like the way line people backup a step... But that has nothing to do ith anything.

Safe, practical and I believe wise, for this pilot.
 
The shudder is completely eliminated in my engine if you pull the mixture at 1000-1200 RPM, then, after the prop has slowed, right before the shudder would normally start just pull the throttle all the way closed. This also seems to make my prop always stop exactly at the position where it is parallel with the ground, every time reliably. If I don't pull the throttle and the end sometimes it'll stop at other angles.
 
spinfire said:
The shudder is completely eliminated in my engine if you pull the mixture at 1000-1200 RPM, then, after the prop has slowed, right before the shudder would normally start just pull the throttle all the way closed. This also seems to make my prop always stop exactly at the position where it is parallel with the ground, every time reliably. If I don't pull the throttle and the end sometimes it'll stop at other angles.
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Mine do that too. It's aggravating. I always have to turn them by hand to set them vertical.
 
I just shut off the ignition switch.. Takes the motor about 1/2 second to stop..:yes:;)...

ps... Mine is (non standard)..:rolleyes2:
 
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