When to lean mixture

African_Swallow said:
I draw to your attention:
§ 91.9 Civil aircraft flight manual, marking, and placard requirements.

(a) Except as provided in paragraph (d) of this section, no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards, or as otherwise prescribed by the certificating authority of the country of registry.

Therefore, no matter what anyone says about leaning procedure works for them, what their chief pilot does, what some Joe who's the best mechanic in the world said in his blog, etc., you're probably going to get 91.9 thrown at you if you fry an engine such that the FAA finds out and you had leaned your engine in a manner other than what the POH suggests.

Aside from this, it is my understanding that the 3,000' mark for leaning is based upon the fact that the engine will not be developing sufficient horsepower above that altitude to cause damage when leaned. Leaning below that altitude at high power settings can cause damage.

One cannot damage a Lycoming or Continental engine with any mixture setting during taxi. This I relay firsthand from Lycoming and Continental reps on a panel discussion I attended.

So, my practice is to always follow the POH for leaning.

-A.S>
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The problem is that the POH is often... wrong, rarely updated and often has procedures that are detrimental to engine life. A great example is the recommendation in many airplane POHs to run your engine 50F ROP, one of the worst places you can run an engine. Even Lycoming and Continental have come out with bulletins with recommendations on how to run their engines that run counter to some POHs. Limitations are another area that may need updating. Almost every POH I have ever read lists 460F as the CHT redline. Many pilots view this as the limit- anything below it is okay. The problem is that if you get much past 400F you are already causing excess wear and tear on that cylinder. When you get to 460 the cylinder is probably in the process of coming apart if you do not take quick corrective action. As I pointed out if you follow the Mooney Ovation recommendation for leaning on takeoff/climb you may have CHTs in the mid 400 range. Not good for engine life.
I've also seen POHs with incorrect/incomplete techniques- the newer Bonanzas come to mind and the short field technique, which is actually sometimes missing. It takes digging into information outside the POH to find the correct technique. Va is another item that will be incomplete in a manual, something that can tear an airplane apart if you do not know how to correct it. Often only the Va for maximum weight is listed- and of course we all know that Va decreases with weight. How often are we truely at maximum gross weight?
So yes, know your POH. But also know about the system you are flying. Get all the information you can but know where it comes from.
 
African_Swallow said:
I draw to your attention:
§ 91.9 Civil aircraft flight manual, marking, and placard requirements.

(a) Except as provided in paragraph (d) of this section, no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards, or as otherwise prescribed by the certificating authority of the country of registry.

Therefore, no matter what anyone says about leaning procedure works for them, what their chief pilot does, what some Joe who's the best mechanic in the world said in his blog, etc., you're probably going to get 91.9 thrown at you if you fry an engine such that the FAA finds out and you had leaned your engine in a manner other than what the POH suggests.

Aside from this, it is my understanding that the 3,000' mark for leaning is based upon the fact that the engine will not be developing sufficient horsepower above that altitude to cause damage when leaned. Leaning below that altitude at high power settings can cause damage.

One cannot damage a Lycoming or Continental engine with any mixture setting during taxi. This I relay firsthand from Lycoming and Continental reps on a panel discussion I attended.

So, my practice is to always follow the POH for leaning.

-A.S>
Click to expand...

I don't have time to spell it out right now (gotta run, back later), but if you think about the term "operating limitations" for a bit you might back off from some of the conclusions that you reach here. :pirate:
 
African_Swallow said:
I draw to your attention:
§ 91.9 Civil aircraft flight manual, marking, and placard requirements.

(a) Except as provided in paragraph (d) of this section, no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards, or as otherwise prescribed by the certificating authority of the country of registry.
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The only problem with this post is the manufacturer "recommends" a certain leaning procedure. So, it's not a placard, or operating the equipment outside of any operating procedure if you choose to lean a certain way. As long as you operate within the limitations of the aircraft your flying, do whatever you want to do. Show me a placard that requires you to lean to a certain setting and I'll eat my own underwear.
 
mshunter said:
The only problem with this post is the manufacturer "recommends" a certain leaning procedure. So, it's not a placard, or operating the equipment outside of any operating procedure if you choose to lean a certain way. As long as you operate within the limitations of the aircraft your flying, do whatever you want to do. Show me a placard that requires you to lean to a certain setting and I'll eat my own underwear.
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Your not sugesting that a pilot should use common sense and logic are you? Better be careful not to step outside of the profiles or the CP might strike you down.
:cwm27:
 
TFaudree_ERAU said:
Carrying this habit into fuel injected engines is a great way to crack an engine block or fry some cylinders. Just ask the SR20 owner that's based on the field here with us.

If you're having to lean the engine to keep carbon deposits off the plugs, it's time to have your mechanic look at the idle mixture setting.
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There is NO WAY you can damage ANY mainstream (Lycoming or Continental) aircraft engine by idling it too lean. High power settings, yes. Idling/taxiing-NO.
 
I can't lean on my engine while it is running. It sits under the cowl and is very close to the spinning fan. I am able to lean on it when it is parked and the cowl is removed, but even then its greasy and I don't find it comfortable.
 
tfaudree_erau said:
carrying this habit into fuel injected engines is a great way to crack an engine block or fry some cylinders. Just ask the sr20 owner that's based on the field here with us.

If you're having to lean the engine to keep carbon deposits off the plugs, it's time to have your mechanic look at the idle mixture setting.
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owt alert!!!!
 
ryan1234 said:
I've been under the impression that it's a good thing to lean prior to take off under humid conditions as well, despite humidity having a lower impact on density altitude...does that sound about right? Something about the water vapor having an overall cooling effect on the cylinders?
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I cannot believe nobody quoted this!!!

Humid air is less dense than dry air and will therefore limit the engine maximum power output, but the difference between 50% RH and 100% is probably not substantial enough to require leaning at 100msl because outside relative humidity is 100%.

dont lean prior to takeoff below 3000ft DA and even then, do it cautiously.
 
SteveC said:
I don't have time to spell it out right now (gotta run, back later), but if you think about the term "operating limitations" for a bit you might back off from some of the conclusions that you reach here. :pirate:
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:yeahthat:

If it's not in Section 2 it is not a limitation. You should consider the guidance in the POH/AFM, but unless the mixture leaning procedure is written as a limitation it is advisory.
 
TFaudree_ERAU said:
Carrying this habit into fuel injected engines is a great way to crack an engine block or fry some cylinders. Just ask the SR20 owner that's based on the field here with us.
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Meh. Leaning for ground ops is actually called for in the current Cessna T182T POH.
 
Oh, and as an aside, can we all agree that its a bad idea to ask Cirrus owners anything? Clearly they've already exhibited poor judgment. ;)
 
Autothrust Blue said:
:yeahthat:

If it's not in Section 2 it is not a limitation. You should consider the guidance in the POH/AFM, but unless the mixture leaning procedure is written as a limitation it is advisory.
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Are you sure? Check out Footnote 7 in this NTSB case (failure to perform a magneto check is a violation of 91.9(a)). The NTSB appears to regard (at least in that case) all of the manual as setting forth operating limitations.
 
Here's the wording of 91.9a
(a) Except as provided in paragraph (d) of this section, no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, (That's Chapter 2 of Modern AFMs) markings, and placards (That's the big sign on the dash that says "INTENTIONAL SPINS PROHIBITED"), or as otherwise prescribed by the certificating authority of the country of registry (Things like MU2 Currency Training or Cessna Caravan max passenger allotments)
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Unless something in the POH indicates that a check of the mags must be done prior to each and every takeoff, I think the NTSB is wrong in their interpretation of 91.9a, but that's just me.
 
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