Cessna 172R, 172S - "Mixture Idle Check"

eetrojan

eetrojan

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eetrojan
Can any of you more experienced folks explain what the author of this checklist for a Cessna 172R or 172S is doing in step 4, and why?

Cessna 172R, 172S Runup Checklist.jpg
 
My experience with my 172 is I want to see a 50 RPM rise in shut down with the mixture, is this a mistake on the check list?
 
If you lean it, you should get at least a 10 rpm rise and a maximum of 50 rpm rise as you lean to Peak EGT is what I suspect considering the check list it's on. If you go all the way to shut down, you should about a 75 rpm rise just as it shuts down. It's a rough check on the system performance and settings.
 
Cessna simply left that item in when they switched to the injected engine. to do other wise means the must rewrite the POH / Owners manual/flight manuals and get them all approved the the certification process.
 
Tom-D said:
Cessna simply left that item in when they switched to the injected engine. to do other wise means the must rewrite the POH / Owners manual/flight manuals and get them all approved the the certification process.
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Except that the OP's checklist is not the checklist in the POH. The "Mixture Idle Check" item does not appear in either the factory 172R or 172S manual.
 
Pilawt said:
Except that the OP's checklist is not the checklist in the POH. The "Mixture Idle Check" item does not appear in either the factory 172R or 172S manual.
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Then , what is he reading? I don't have a R or S POH.

Or should I be asking why anyone would read any other check list than what in the POH?
 
Tom-D said:
Then , what is he reading? I don't have a R or S POH.

Or should I be asking why anyone would read any other check list than what in the POH?
Click to expand...

People make their own checklists
 
It has to do with checking the idle/mixture set screws and fuel circuit.

If you get a rise way over spec or no rise at all, there's something wrong with your carb...
 
I fly both models and never do a mixture idle check.
 
Thanks All.

The checklist is provided by the flight school. The same entry re a “Mixture Idle Check … 10/50 RPM MAX RISE” appears in the checklists for both the Cessna 172R and the 172S, i.e. for the two models with fuel injected engines.

I didn’t author it. I’m asking about it, though, because I’m working on my own custom checklist and, so far, I can’t find anything supporting it in the POH or anywhere else.

The item does not appear in the school’s custom checklist for their older, carbureted Cessna 172P, nor so far as I can tell, in the POH for the 172P, 172R, or 172S.

Since I will be doing my instrument training in these planes, I wanted to completely understand them. I don't currently have an instructor to ask, so you're my huckleberry.

I’m certainly not positive, but I think Henning’s comment in post #3 may be on the right track. But, if it’s not mentioned in the POH, is it just a known technique borrowed from somewhere else?

Thanks again for any speculation or insight!
 
Luvrv8 said:
My experience with my 172 is I want to see a 50 RPM rise in shut down with the mixture, is this a mistake on the check list?
Click to expand...

No. It's a check to ensure your engine has its idle mixture setup properly. It's important and it sounds like your engine is just right.
 
Pilawt said:
In fact, on checking the old manuals in my file, it doesn't appear that the "Mixture Idle Check" item has ever been in any factory-published checklist for the C-170 or C-172.
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Probably because it doesn't make much sense to do, normally you do the check on shutdown, and it's really a maintenance check, not a pilot check.
 
jcepiano said:
I fly both models and never do a mixture idle check.
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Pilots almost never do unless they are mechanics, then it's just part of normal shut down to watch for a rise on the tach. Not sure why someone put it on that list.
 
Originally Posted by Tom-D
Cessna simply left that item in when they switched to the injected engine. to do other wise means the must rewrite the POH / Owners manual/flight manuals and get them all approved the the certification process.
Click to expand...


Pilawt said:
In fact, on checking the old manuals in my file, it doesn't appear that the "Mixture Idle Check" item has ever been in any factory-published checklist for the C-170 or C-172.
Click to expand...

:rolleyes:

:rofl:
 
register@teamandras.com said:
Thanks All.

The checklist is provided by the flight school. The same entry re a “Mixture Idle Check … 10/50 RPM MAX RISE” appears in the checklists for both the Cessna 172R and the 172S, i.e. for the two models with fuel injected engines.

I didn’t author it. I’m asking about it, though, because I’m working on my own custom checklist and, so far, I can’t find anything supporting it in the POH or anywhere else.

The item does not appear in the school’s custom checklist for their older, carbureted Cessna 172P, nor so far as I can tell, in the POH for the 172P, 172R, or 172S.

Since I will be doing my instrument training in these planes, I wanted to completely understand them. I don't currently have an instructor to ask, so you're my huckleberry.

I’m certainly not positive, but I think Henning’s comment in post #3 may be on the right track. But, if it’s not mentioned in the POH, is it just a known technique borrowed from somewhere else?

Thanks again for any speculation or insight!
Click to expand...

Put it in you shut down check to watch for it when you pull to ICO. You want to see 50-75 rpm rise, otherwise it is too lean. If it's too rich it runs like crap so it's obvious.
 
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I was able to get some comments from my former PPL instructor re the mysterious (to me) runup entry for "Mixture Idle Check … 10/50 RPM MAX RISE". Consistent with Henning's post #15 re it being a "maintenance check," he says that I should ignore it during runup, that it's "just for maintenance."

I have no idea why they keep this on their daily-driver checklists. :dunno:
 
register@teamandras.com said:
I was able to get some comments from my former PPL instructor re the mysterious (to me) runup entry for "Mixture Idle Check … 10/50 RPM MAX RISE". Consistent with Henning's post #15 re it being a "maintenance check," he says that I should ignore it during runup, that it's "just for maintenance."

I have no idea why they keep this on their daily-driver checklists. :dunno:
Click to expand...

When you embrace the fact that 80% of human beings are stupid, life becomes much less confusing, you just look at stuff like this and think, "Oh, that's stupid." And move on.:lol:
 
Henning said:
Pilots almost never do unless they are mechanics, then it's just part of normal shut down to watch for a rise on the tach. Not sure why someone put it on that list.
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This pilot/ instructor does it on every pre-flight run-up, and teaches it that way.
I want to know if the mixture setting is good BEFORE the flight, if it is serious.
 
Nosehair my friend - Can you elaborate why you do it and teach it and on how you do it? Also, where can I learn more about it? Thanks!
 
I always thought "Mixture Idle Check" was after leaning the plane before take off, after the run up, you pull the throttle back to Idle, to see if the engine would still have enough fuel to keep the motor running when you chopped the power on approach, or elsewhere.

A rich enough mixture at 1700 rpm might not run at 600? Hence, "Mixture Idle Check".
 
Hey! the IDLE mixture check is done at IDLE, otherwise they would not cal it an IDLE mixture check.

Come on guys get real.
 
JoseCuervo said:
I always thought "Mixture Idle Check" was after leaning the plane before take off, after the run up, you pull the throttle back to Idle, to see if the engine would still have enough fuel to keep the motor running when you chopped the power on approach, or elsewhere.

A rich enough mixture at 1700 rpm might not run at 600? Hence, "Mixture Idle Check".
Click to expand...

This particular "Mixture Idle Check" is looking for an RPM rise (10/50 RPM Max), so it must not be that kind of idle check.
 
That's right. An "idle check" is to check that the idle position won't quit when you pull to idle on final. To do it realistically, the mixture should be in the anticipated position it would be on final, probably full rich, but not necessarily. I do it after the mag check runup, I bring the throttle sharply back hard against the stop, trying to see if it will quit, then let it idle 10 - 15 seconds to see if it idle smoothly, then back up to recommended idle.
I had one quit in flight at idle, so I check - checklist or not.

In a separate check on the mixture, before the runup, with the tach needle precisely on the 1000 rpm line, so I can see the slightest movement, I squeeze the mixture back from full rich to see if it rises about 25/50, then starts dropping, which is what it should do because it is a little rich at the full in position.
If it gains 100/200 rpm, which it will on an extremely hot day, 100°F or so, or at highaltitude airports, or at combinations of the two, then I know to set the mixture to best rpm for take off, and not to go full rich before landing.
 
nosehair said:
That's right. An "idle check" is to check that the idle position won't quit when you pull to idle on final. To do it realistically, the mixture should be in the anticipated position it would be on final, probably full rich, but not necessarily. I do it after the mag check runup, I bring the throttle sharply back hard against the stop, trying to see if it will quit, then let it idle 10 - 15 seconds to see if it idle smoothly, then back up to recommended idle.
I had one quit in flight at idle, so I check - checklist or not.

In a separate check on the mixture, before the runup, with the tach needle precisely on the 1000 rpm line, so I can see the slightest movement, I squeeze the mixture back from full rich to see if it rises about 25/50, then starts dropping, which is what it should do because it is a little rich at the full in position.
If it gains 100/200 rpm, which it will on an extremely hot day, 100°F or so, or at highaltitude airports, or at combinations of the two, then I know to set the mixture to best rpm for take off, and not to go full rich before landing.
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Do you have a reference for any of that?
 
If you're in flight at idle, why do you care if it dies? It'll come right back up when you put the throttle back in.
 
Henning said:
If you're in flight at idle, why do you care if it dies? It'll come right back up when you put the throttle back in.
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Not if it happens in a 172 when you have full flaps and you pull the throttle to do a power off stall. The prop will stop. The student next to you will about have a heart attack. Not a huge deal assuming the starter will work. If the starter doesn't work, you can get it to spin again with air, but you have to get damn near Vne (in a 172) to make it happen.
 
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Quick question for you learned guys.

172SP 180bhp fuel injected, would you still lean the mixture for taxi/idle or does the engine management take care of it depending on the RPM setting ?
 
Read your POH. It's in there for SPs, including a detailed technique for doing it. Fuel injection does not lean the mixture at idle.
 
Tom-D said:
Do you have a reference for any of that?
Click to expand...

Proper fuel/ air mixture is dependent on air temperature and density altitude.
The mechanic sets the full rich position based on an average setting for season and location. This setting will be too rich on hotter days or at higher altitudes.
When the POH says lean above 3000', that means 3000' density altitude, and that can be at airport elevation on really hot days.
You don't have to be in Denver to apply good mixture control.
By doing this as a routine procedure, my students are not afraid of leaning in flight. They have taken the time to feel and see the procedure on the ground, and routinely lean to best power in all flight conditions.
 
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I know this is an old thread, but it comes up at the top of a Google Search for 172 idle mixture. The most likely reason for the flight school putting the check on their check-list is because of 2001-CE-14-AD They're erring on the side of caution, having everyone check the idle mixture on every flight. The AD does not require it, but then checking it is not necessarily a bad thing either especially on heavily used (and abused) flight school planes.
 
I don't want the engine to die at any time if I go to idle. My CFI pulled the throttle probably 15 times during training, and I worried every time that it might die if we were at low altitude. The piece of crap battery they have in the 172 I rent barely gets it started on the ramp.
 
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