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“Never lean using EGT when operating at more than 80% power.”

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Aircraft Systems, General Aviation

As a student pilot, I was reviewing my POH and recently came across the following sentence in bold print: "Never lean using EGT when operating at more than 80% power."

Why?  What would happen if I did lean using the EGT gauge at more than 80% power?

My fear is that I may deviate from the performace figures listed in the POH and unknowlingly run at more than 80% power.

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1 Answers

  1. John D. Collins on Mar 15, 2011

    You should follow your POH recommendations.  At high power settings, an extra rich mixture is used to help cool the engine and maintain an adequate margin from detonation occurring in the cylinders.  The higher power settings generate higher internal cylinder peak pressure, a rich mixture reduces the peak pressure.  Unless you have a turbo charged (or normalized) engine, 80% power can only be achieved below 6000 or 7000 feet.  If you have an EGT that shows a digital temperature number, if you note the EGT at full power on takeoff, it is usually OK to lean to that temperature as you climb. For most engines, the recommendation in the POH is conservative.



    On a turbo normalized engine such as the IO550N used in the Cirrus SR22TN airplane, they allow for two different methods of climb leaning, full rich at around 35 GPH or lean of peak at around 85% and 18 GPH upper limit.  However, they also note that the CHT and TIT (Turbo Inlet Temperature) need to be kept within acceptable bounds.  To cool the engine further, either lean to a lower fuel flow or go to full rich.  I only point this out to note that different airplanes with different engines have their own restrictions.


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