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3 Answers

High Airport Elevation Operations

Asked by: 2895 views Aircraft Systems, Student Pilot

I’m a student a pilot and I have taken lessons at sea level airports. I moved to Colorado (high elevation over 5,000 ft.) and will be continuing my flying lessons here, in a 70’s model Cessna 172. I know the air is thinner at the higher elevations which will require me to lean the mixture more and prior to takeoff lean for maximum RPM. The aircraft POH doesn’t explain much about High Airport Elevation procedures except to lean it above 3,000. I was taught to lean the mixture 1 inch during taxi ops at sea level (to prevent the magnetos from fouling?) then full rich for runup and takeoff. Do I need to lean it more for taxi ops at higher elevation? Do I go full rich at high elevations during runup to check the magnetos or do I leave it lean? Do I conduct a full power runup and lean the mixture for max RPM in the runup area or wait until I get until I line up and wait on the runway and do it then? If I already leaned the mixture prior to takeoff at a 5,000 ft airport elevation and climb to 10,000 I’ll still need to continue to lean the mixture as I’m climbing right? 

As you can see I don’t know much about this type of operation. What type of procedures do some of you flight instructors teach your students?

Thanks for your help!

 

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3 Answers



  1. Aaron Strasburg on Feb 01, 2013

    Your school should have their own procedures, but here’s what we use for our runup: lean to max RPM, then richen 3 half-turns. The rest of the runup should be the same. This is at a 5800′ airport, so very similar.

    For taxi you can lean until the engine runs rough without issue. You just need to start the runup at full rich.

    The starting elevation doesn’t affect the leaning procedure during the climb.

    Not a CFI, but I do fly out of a pretty high airport.

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  2. Mark Kolber on Feb 02, 2013

    Depending on where you are, if it is one of the Front Range airports, the method you will be taught will be about the same or a minor variation of the one Aaron describes (I used to teach there).

    The one thing to be aware of is that the “enrichen 3 turns” after reaching max rpm is a shortcut approximation based on experience with the airplane. If you ultimately go for your complex endorsement and fly a Cutlas, you’ll find that 3 turns won’t be enough.

    The extended version of the procedure, which you may end up using if you fly into one of the really high Colorado airports or on a really warm day, involves setting the mixture at max rpm at full power. The “enrichen 3” at runup shortcut recognizes that your fuel needs will be greater at full takeoff power.

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  3. David Brown on Feb 13, 2013

    The OP was referring to an altitude of 5000′, not somewhere down around 1500′.

    I am rather unimpressed with the notion that the runup be done at full rich. At 5800 feet that is a bad idea. It is actually a less than ideal method at sea level as a fully rich mixture runup masks many weaknesses in the ignition system.

    At a high altitude you are running far too rich with the red knob in.

    If the aircraft has a digital EGT, and the probes are in the right places an EGT of 1250-1320dF would be an ideal mixture to use for maximum power, and far more performance than you will get full rich, and yet still kind to the engine in terms of peak pressure and CHT.

    If you only have a single point EGT (typical in a Cutlass) you or the school should find the number or position on the scale where a sea level takoff would achieve, and use that as your target EGT. So at the point of applying power, roll in throttle and then mixture until you have achieved max RPM and keep rolling in the mixture until the target EGT. There should only be a very slight RPM drop.

    Take offs from high altitudes, and especially in summer where the Density Altitude is up around 9-10K’ is not a shoot from the hip proposition, and done full rich is potentially deadly. People have died from doing this wrong

    Have a read of the Pelicans Perch articles by John Deakin on AvWeb or better still sign up for a course by John and co at http://www.advancedpilot.com

    It could be a life saver!

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