The EXTREMELY helpful guide to Density Altitude

[@NickLaoutaris]

that should have a million views.

[@ScottKoonCFI]

Thank you! I hope it does get a million views. Take care!!

[@JohnG-u7f]

Indicating that Density Altitude is already accounted for in performance charts was a significant revelation. Understanding how temp effects air density is easy enough, but pointing out that we don't use it in day-to-day flight planning was enlightening and "relieving".

[@ScottKoonCFI]

Excellent! I’m very glad it was helpful! Thank you for the comment!

[@PaulCrooks-x4j]

The question was really. Find the DA alt reads 30.35 ,RW temp of 25 deg F airport elevation 3894. A2000 ft B 2900 ft C 3500ft AnsA

[@ScottKoonCFI]

Thanks. That is helpful. First, I’ll say I don’t have that Gleim book (mine is several years old). But I have a couple of comments. To calculate Pressure Altitude precisely enough for your written, it will require using an electronic E6B or the chart in the testing supplement. There is a “shortcut” that provides a quick PA that can be used for flight planning, but won’t get close enough for the written. I explain that more in this video: Checkride prep | Aviation Math | How To Calculate Pressure Altitude kzbin.info/www/bejne/gZTMpHqeqa6cnac Using the testing supplement chart and Interpolation would give a PA correction of -394 making the PA 3500 ft. Using the formula, the new PA, and the Temp in C gives a DA of either 2060ft or 2073.32ft depending on how you round (or not). Using -4C and 3500PA on my whiz wheel E6B shows ~2000ft. Using the chart and 25F shows exactly 2000ft. For grins, I used my electronic Sporty’s E6B and it came up with 2043ft. As for the variability, it likely comes down to the number of significant digits and rounding used. In all these cases, 2000ft would be the “best” of the three test answers presented. I hope this helps. Thanks for asking the question and thanks for presenting the opportunity to practice.

[@PaulCrooks-x4j]

212 page on Gleim question 11

[@ScottKoonCFI]

I’ll go look.

[@nw6198]

I have to admit, I wish you were my personal CFI. Your enthusiasm is encouraging and your explanations are clear and cut through the jargon. I am looking forward to seeing all you videos. If you had a whole ground school program, I would definitely buy it if it were of this quality and accessibility.

[@ScottKoonCFI]

Thank you very much for the comment. I am working on a course. Hopefully, it will be ready in time for you to use! Stay tuned!

[@nw6198]

@@ScottKoonCFI I've still got to get the funds for training situated, so I might be looking into it by the time you're done, lol.

[@ScottKoonCFI]

Understood! I’ll keep the channel updated!

[@jimminithecritic8623]

Thank you, this really helped me before my stage check

[@ScottKoonCFI]

Excellent! I’m glad it was helpful and hope your stage check went well! Thank you!

[@tharsim]

I had to pause at "in plain English" to giggle

[@ScottKoonCFI]

Excellent! Thank you for sharing! Have a great day!!

[@MonicahWanyoike-tf1pt]

Good job🎉on explaining

[@ScottKoonCFI]

Thank you. I’m glad it was helpful!

[@ryanhernandez9995]

Awesome video the explanation was been amazing. I am currently getting my A&P license and we have an assignment on density altitude but I had a question with writing the formula for the ISA. let’s say the PA is 7400 would .2 be correct for the ISA.

[@ScottKoonCFI]

Thanks for the comment and the question. For the purposes of flight planning, the answer is “Yes. The answer is 0.2”. My question back to you would be, “how accurate is your instructor expecting you to be?” The reason I ask is because if you look at the FAA documentation, they list the standard lapse rate at 2C per 1000 feet. However, if you look at the ISA documentation they list the lapse rate at 6.5C per 1000 meters. That actually works out to be about 1.98C per 1000ft. So, if your instructor is looking for a more accurate number, then you either need to convert the PA to meters and use 6.5C or use 1.98C with feet. The first results in 0.33912. The second results in 0.348. I hope this is helpful without being too confusing. Thanks again for the comment and question.

[@ryanhernandez9995]

@@ScottKoonCFI no not too confusing lol. But the assignment did list the 2c per 1000ffeet stipulation however he was not looking for accuracy but more of just to use a Density Altitude Chart but at the time i was not 100% sure how to read one, but formulas are plug and play so i used that instead. but thanks to your video i am getting better at it.

[@ScottKoonCFI]

@ryanhernandez9995 Glad it was helpful!! Best of luck!!

[@greentom4194]

hi Scott,what's the difference between true altitude and denstity altitude? They both calibrate the pressure and temperature deviation from ISA, so why we don't just use one of them?I asked many people,nobody can give me a convincing answer.

[@ScottKoonCFI]

Thanks for the question. If you’ve asked a lot of people and didn’t get a good answer, I’m not sure I’ll be able to do better, but I’ll try. True Altitude is the height above Mean Sea Level. Non-ISA temperatures or non-standard pressures don’t affect True Altitude. This altitude is used for determining relative elevation for things like obstacle clearance. For example, my home airport is 1,317 ft above MSL (True Altitude) today and will be for the foreseeable future regardless of the air pressure or temperature. I know there are some calculations concerning temperature and True Altitude, but I’ll get to those in a minute. Density Altitude is Pressure Altitude corrected for non-standard temperature (and humidity). This is a calculated value based upon comparison to ISA. This value is used for performance calculations, not obstacle avoidance. Unlike True Altitude, this value will change as the weather changes. Where this gets confusing is when you also consider Indicated Altitude. Indicated Altitude is what is shown on your altimeter. Altimeters are calibrated using standard atmospheric conditions, but are also influenced by pressure and temperature. We can correct for non-standard pressure using the altimeter setting, but there is no real way to recalibrate the internals for non-standard temperature. The equation for True Altitude-Indicated Altitude + (ISA Deviation × 4/1000 × Indicated Altitude)-is not to *calculate* True Altitude, but rather to *correct* Indicated Altitude so that it more closely approximates True Altitude. I hope this helps.

[@greentom4194]

@@ScottKoonCFI Thanks Scott,you are an expert.Only you solved my problem.You are the best aviation youtuber.

[@ScottKoonCFI]

I’m so glad that was helpful! Thanks for the comment and the question!

[@AquilesFinol2009]

Thanks it will help me with aviation test since my teacher dint really teach it rifht

[@ScottKoonCFI]

I’m very glad this was helpful!

[@Ludwing730]

Really good video thank you.

[@ScottKoonCFI]

Thank you so much for the comment! I’m glad it was helpful!

[@NickLaoutaris]

yeap , this guy is amazing ! best CFI ever. Love his videos.

[@ScottKoonCFI]

Thank you so much! Have a great day!

[@excellenceinanimation960]

Amazing videos!

[@ScottKoonCFI]

Thank you! I’m glad they are helpful!

[@AaronWbirdman]

Love it!

[@ScottKoonCFI]

I'm so glad! Thank you!

[@SkyRizzy33]

Very precise video

[@ScottKoonCFI]

Thanks!

[@manwinkler]

excellent ... thank u for sharing

[@ScottKoonCFI]

Thank you for the comment!

[@ZenithE8]

Please tell me theyre not going to ask that the math be done on the written?

[@ScottKoonCFI]

Nope. How you arrive at the density altitude is up to you. I wanted to show three methods to demonstrate they arrive at the same answer. The chart is in the test supplement (so you can definitely use that). You should also have your E6B with you (either electronic or whiz wheel). So don’t worry about having to remember the formula. Thanks for the question. Best of luck on your written.

[@ZenithE8]

Thank you. :)

[@PaulCrooks-x4j]

I did a problem with PA 3400 and temp 25 deg F and did get the book and of 2000 using the formula

[@PaulCrooks-x4j]

Please comment

[@ScottKoonCFI]

Sorry Paul, I’m not sure I understand the comment/question. Are you saying you used the formula and the answer you came up with was different than the answer in the book you were using? If that is true, then let’s walk through the problem and see what we come up with. They’ve already given Pressure Altitude at 3400. That is one less step you’ll need to calculate. However, they did throw a curve ball. They gave the temp in F. For the formula to work you’ll need to convert to C. Google converts 25F to -3.889C. Using the information from the video, the ISA temp for 3400FT should be 15C - (3.4 *2) or 8.2C. Subtracting the two temps (-3.889 - 8.2) = -12.089. Multiply -12.089 by 120 = -1450.68 Finally, adding 3400 and -1450.68 = 1949.32 ft Density Altitude. I’m not sure what the other options were, but rounding “pessimistically” would give us 2000ft. On my E6B, the temp conversion chart only shows whole numbers, so 25F converts to about -4C. The altitudes are in thousands of feet so, approximating -4C and 3400 pressure altitude does show a density altitude of approximately 2000ft. Finally, using the chart from the testing supplement does allow you to use 25F. But you need to approximate the 3400 PA. Finding the point at 25F and just under halfway between 3000 and 4000 PA does provide a density altitude of just under 2000ft. Hopefully, walking through these helped. Thanks for the comment.

[@PaulCrooks-x4j]

Thanks

[@alxaer]

Hi Scott, you really make a difference with these videos, they are engaging and this makes it so easy to watch and absorb the knowledge past rote memorization.

[@ScottKoonCFI]

Thank you so much for the comment! I am glad they are making a difference!