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When to lean?

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Well-known member
Jan 20, 2009
Currently I'm flying a PA-28 181 for my boss and he insists on leaning the mixture all the time. Problem is he just pulls the mixture back to where ever he feels like and he does this at any altitude. I thought you leaned above 3000ft? He does this all the time when we are shooting approaches where we are at 2100-2400 ft msl, then going missed and adding full power still leaving the mixture leaned. Can someone chime in with some advice, because this is not how I learned how to lean. Thanks
GUMPS check before landing should keep from choking engine on go-around.
Lean to enroute altitude and T/O and landing elevation. In high performance piston A/C durring extended climb with injected engines I will use rich mixture to cool cht in high oat.
In most light airplanes, including a PA-28, lean at all times, except when at full throttle for take-off. Even on take-off, if you are approaching 3000 DA which can happen at a sea level airport on a 90+ degree day, you should lean prior to take-off to get best power.

Flight schools (the flight training system) don't teach proper leaning, because:
1) Too Complicated - Old School; not worth the time and effort since it is not tested on the checkride. Trim that from the training system.
2) Old School Fear that students will lean excessively and cause engine damage. This is the main reason most rentals are "wet". Dry rentals would cause pilots to learn leaning, but may encourage excessive leaning. I don't think so, but maybe so...

...in any case, you should lean until you get a good smooth rpm. You may get a slight increase, then smooth out, ot the rpm may just begin a decrease with no prior increase. In this case, push the mixture back in until it returns to the point the decrese was noted and the engine is smooth.

Practice on the ground during run-up. Find the best power position of the mixture when at run-up RPM. This would be the best power take-off position except that the small tightly enclosed engine needs extra cooling for the full-power low airspeed climb. At sea-level / near sea-level airports.

As soon as you come back off of full throttle, or approach 3000 DA (density altitude - not what you are reading on the altimeter) you should be leaning to get best power.

I prefer to fly small engines on approaches with the mixture still leaned, since I will get best power during the approach or go-around. I have, and teach, the habit of pushing ALL knobs forward in the go-around, ie, throttle(s), prop(s), mixture(s), carb heat(s), etc. All knobs around the throttle - not just the throttle. Even if you prefer to push the mixture rich during approach, this go-around technique saves a senior moment on the approach.

But...having mixture rich during approach can cause a decreased power availability in high altitude approaches, and can increase spark plug fouling which happens all the time the engine is running at low rpm with a full rich mixture. I have had an idling engine quit on final because the mixture was rich and it was a hundred degrees out.

Bottom line here is that flight schools, and most independent instructors do not teach mixture leaning, neither do we teach selective use of the carb heat. (on a Cessna) Just use it all the time; even when it's a hundred degrees out.
Nosehair's advice is spot-on and useful as always but I have a couple of non-technical comments.

You are not flying the Archer for your boss. If he or she is operating the engine controls without your concurrence, they are the pilot. You have to ask yourself why you are aboard on that flight.

If you still feel compelled to get in the airplane with this person, offer to pay the cost of their fuel savings from constant leaning up front in exchange for them leaving the mixture rich. On a typical flight behind an O-360, that should set you back about five bucks.
I thought you leaned above 3000ft?
The number may be three grand, some manufacturers it's four grand, and all that number represents is a wave at stupid pilots. Providing a general wasteful counsel to lean above those altitudes is an attempt at idiot-proofing the leaning practice because manufacturers know that pilots are seldom taught to lean properly, that pilots seldom remember, that pilots are generally dense enough that providing a blanket direction like that is really the only way to encourage pilots not to do something damaging to the airplane.

Have you ever stopped to wonder why the manufacturer provides a general counsel to refrain from leaning below 3,000'? Is it because there's a problem with leaning below that altitude? Of course not.

The reason that pilots are cautioned about leaning below certain altitudes is because a normally aspirated engine above those altitudes can't be run at a power setting high enough for a pilot to screw up the leaning procedure and damage the airplane. Once an engine is powered back below 75% power, you're not going to hurt it by leaning. You're not going to get into detonation issues by leaning, you're not going to be burning valves by leaning, you're seldom going to cause CHT issues or approach EGT limits (where applicable) at lower power settings. Lean away.

Manufacturers also don't encourage lean of peak operations for the same reasons. Is operating lean of peak harmful? Nope. It's helpful to an engine, and the better way to operate...but only if done properly, and in context.

Can you safely lean below 3,000'? You bet. Can you safely lean above 75% power? You bet. Can you operate at power settings less than 75% power below 3,000'? Sure.

The altitudes provided by manufacturers are altitudes at which typically you can't produce enough power at full throttle to go past 75 to 80% power...the altitude at which you can't hurt the engine any more by leaning, no matter how hard you try.

In truth, if you fail to note your cylinder head temps and fly at too low an airspeed, mismanage cowl flaps, or do other things wrong, you can still hurt the engine, but the altitudes published for leaning procedures are efforts at attempting to reduce the chances for untrained pilots to do dumb things. That's all.

You haven't described your boss. Is he a pilot? Non-pilot? Instructor? Have you asked him to discuss his leaning practices? You might learn something.

Presently your description suggests that you don't understand engine operation or leaning: now is as good a time as any to get educated.

If you still feel compelled to get in the airplane with this person, offer to pay the cost of their fuel savings from constant leaning up front in exchange for them leaving the mixture rich. On a typical flight behind an O-360, that should set you back about five bucks.

I find that behind an O-360 I typically use about 25% less fuel than most. Over the course of a few hours, that adds up to more than five bucks. Proper leaning does more than merely save fuel, however. Proper leaning is essential and appropriate to improved engine health.
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My boss is a pilot. He is working on his instrument and his leaning technique is to just pull the mixture back. No thought process involved at all just pulls it back. I came on here to learn and boy did I ever. Thanks for the information I'm glad I was wrong and got a correct answer and not just a lean the damn thing all the time answer.
Turn right- lean right,
Turn left - lean left..
go up, lean back, go up faster- recline seat back
Go down - lean forward, down faster - lean forward and push yoke forward too..

Hey just kidding around.. good info on here.. this is what Flight Info is all about!!. good job!

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