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How To Calculate Density Altitude

by Jason Schappert

I never realized how important it was to calculate and understand density altitude until my trip flying the 150 across America. You really get to know Density Altitude first hand as you’re cross over mountain ranges with a 200fpm climb rate!

So in this video I want to show you a neat formula to calculate Density Altitude.



What’s been your experience with Density Altitude? How do you calculate it? Let me know in the comment box below.

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  • Roger Waters

    Great video! As you know I’m new to flying. I’m trying to take it all in by reading tons of stuff but have been frustrated with a simple explanation of density altitude and how effects flight. You turned my feeble light on with the statement “it’s the altitude at where the plane feels like it’s at”!

    Thanks!
    Roger

  • Marc

    What is the difference that a turbocharged engine makes over a non-turbocharged engine in a given density altitude?

  • Dfg1958

    Seems easy enough. Will cross check this when I get home against the electronic E6B.

  • Tracysmithppasel

    Hi Marc:

    You ask a great question.  A non-turbocharged aircraft can only suck in as many oxygen molecules as the atmosphere can deliver – as we increase altitude, and that includes changes in density altitude – those molecules get fewer & fewer, therefore less & less power available.  A turbocharged aircraft will use an ‘air compressor’ (the turbo) to pack air into the cylinders – typically to sea level pressure – so the aircraft retains performance with changes in altitude and density altitude.  When the aircraft boost level is set up to sea level pressure we usually refer to that as being ‘turbo-normalized’. 
    Hope this helps.
    Tracy

  • Vince Inzinna

    After looking at your formula, if you had to do the calculation quickly in your head you could just say that for every degree C over 15C, just add 120.  If it were 22C for example, just add 7 x 12o, or 840 to your pressure altitude.  Same thing as you’re doing, just said a different way. 

    By the way, does that work on the “backside” of the temperature curve too?  In other words, if it were 10C, would you SUBTRACT 5 x 120, or 60ft from your elevation? 

    Enjoying your website.  Keep up the great work.

  • Stealth114

     Jason.. Another great vid.. Thank you for posting.. Im just curious on
    how you derived the formula.. Also, the (  OAT – ISA ) , will the ISA
    temperature in the equation be the value at sea level ( 15 C) no matter
    what pressure altittude we are calculating  or will it be the ISA
    temperature at that altitude.. Cheers.. Niv

  • Tracysmithppasel

    Hi Vince:

    No, it does NOT work backwards.  Density Altitude can never be less.
    I really like your shortcut !

    Tracy

  • Leyva1998

    nice video, just to point out to new students to keep in mind that most aviation temperatures are in C (Celsius) not F (Fahrenheit). It would be good if you explained that you used 15C because you are at sea level. Here in Tucson we are at 2500′ to start, our ISA temp would be 20C, or did I confused that? Thanks

  • Kenn Hinick

    If you really want to experence the effect of density altitude at its max fly into and out of Lake County Airport , Leadville, CO.  The field elevation is 9927 feet with a pattern of over 10,000.  Turbo’s and Turbines can both be taxed on days to get you airborne and sometimes you wait out the day for the next morning.  Having a 1400HP turbine engine have N1 (Compressor) droop while trying to get airborne will make you learn to do your “Homework”

  • Peter

    The density altitude CAN be less than pressure altitude and field altitude – that is the whole point and why your plane performs better on a cold morning at zero degrees Celcius than later when the temperature is exactly 15 degrees.

  • Marc

    I found an error in the pressure altitude formula. To be mathematically correct, there needs to be a bracket around the standard pressure and the current pressure giving:
    Pressure Altitude = (Standard Pressure – Current Pressure)*1,000 + Field Elevation.

  • Tracysmithppasel

    Hello Peter:

    I stand corrected – I should not have used the word ‘never’.
    ‘Density Altitude’ is best thought of in the context of ‘negative performance’..
    WE LIKE positive performance – so improvements are not a concern !!!!
    However, to be absolutely correct, you are indeed right.  My concern is that student pilots just might think of Density Altitude as a good thing at a bad time.  So, my apologies to all.

  • Jason

    Jason Im a new pilot how could I find pressure altitude for figuring cruise performance if im planning a X/C.

  • Craig

    I love flying to Leadville here in Colorado! Only problem is that I have to wait for winter to take the 172 there.

  • Jim

    Still totally confused…I’ve read so many variations of calculating da I don’t know what to think? But thanks for trying!! I’ll get it some day….

  • Dima

    It’s sometimes much easier to use 125 ft per deg.C which equates to 1000
    ft per 8 deg.C. E.g., if difference between Std.T. and OAT is 12 deg.C,
    the extra (density) altitude is 1500 ft.

    Note that the difference between the two formulas is miniscule relative
    to the error due to not taking humidity into account (humidity DOES
    affect the calculation to a large degree, much more than extra 5 ft per 1
    deg.C).

    Another note/correction: the Std.T should not be taken to be 15 deg.C
    regardless of altitude, but instead whatever it is in the “std.
    atmosphere” at the pre-calculated pressure altitude. E.g. if solving for
    conditions at an airport with field elevation of 5000 ft (with, e.g.,
    pressure altitude being 6000 ft, and OAT being 3 deg.C), the Std.T for
    6000 ft is the same 3 deg.C as the OAT, and so the formula would give
    density altitude of 6000 ft (same as the PA), NOT 6000 + 125 * 12 = 7500
    ft.

  • Jvandunk

    I like your videos. My question is how can I get the flare correct on landing? That is my problem.

  • Chris925951

    big bear famious for density altitude 6700 elevation. (L-35). cant go on a hot day mostly in summer.

  • Mark C

    Jason, thanks. I like Dima’s shortcut. I’m writing that one down and committing it to memory and a note attached to my kneeboard, along with my “cheat sheet” for figuring crosswind component.

  • http://pulse.yahoo.com/_6AEI5QV764VD5WSBE7TAFUUBTQ G W

    Great vid.. now please please lay off the meth

  • Bub hallett

    This is for JVANDUNK, to get the correct flare for landing, try looking further down the field. I believe you may be looking too close to the airplanes nose or even straight down. You do not want to see the earth rushing up at you.If you look further down the runway you will see the earth getting flatter and flatter. Bub

  • MO

    great job

  • TMG

    So what do you do with the DA once you know that number?  The aircraft feels like it’s at the DA, does that mean you subtract that number from the ground roll distance for your type aircraft or do you add that to the required ground role and landing numbers?  I just want to be clear now that we have the DA what’s next?

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