I remember a buddy of mine wore a watch for every time he thought he needed. He had one set to local time, one to UTC time, one to Zulu and one to Greenwich, England.
Well said Jason. The lack of respecting density altitude has killed many. Unlike the days before EFBs, we can also find density altitude defined for us in ForeFlight, etc. Still, knowing how to work an E6B is a must have for flight training.👍
I saw a video about a Helicopter rescuing hikers on Mount Everest. The pilot was yelling to only load 2 passengers and no bags. This is why, great video. Know your aircraft performance. Thanks.
This comment is for all of you out there reading the book verbatim, lol! Remember that common sense prevails,....rule number one,..."When in doubt, throttle out! In our case it would actually be throttle "IN!" 😀😀. Jason, keep up the good work, great info as always!
When you do the graph estimation, you should be going up to 112ft rather than sea level, which is the pressure altitude you got from the altimeter correction. Overall a great explanation of density altitude, though - thanks!
Chemist here. Water molecules do not "attach themselves to the oxygen molecules". The reason water molecules (high humidity) lower air density, and raise density altitude is quite simple. Water molecules weigh less than dry air molecules. Dry air consists of 78% nitrogen molecules (N2) and 22% oxygen molecules (O2). Nitrogen molecules molecular weight is 28. Oxygen molecules molecular weight is 32. Water molecules molecular weight is only 18. More water molecules in air, higher humidity, means that lighter water molecules are diluting heavier nitrogen and oxygen molecules. Humid air is, despite the subjective experience, less dense than dry air at the same temperature and pressure.
Thanks, that explains the smaller mass if the number of molecules stays the same in a given volume. Or if each water molecule in average replaces at least more than 0,62 "air molecules" in that volume. Why this would be the case is not obvious to me though.
When I did the Finer Points of Mountain Flying a couple of years ago our field elevation was 5900 feet (KTRK) and the density altitude was routinely 8000 feet in the afternoon. This required careful thought and planning (and a *lot* of runway) on takeoff...
Thanks Jason, this does help....however I always struggle with the interpolations on the FAA test question...e.g.Altimeter Setting is 30.87 vs a straight 30.8 They almost never give you a straight up Altimeter setting.
I know this is a year old but here is how I do these questions. 30.8 = -803 and 30.9 = -893 straight from the Density Altitude table in your study material. Your difference is 7/10's the way to 30.9 from 30.8. Therefore you can find 70% of the difference between -803 and -893 and easily find your answer. -893 - -803 = -90. Multiply -90 * .7 and you get -63. Add that -63 to -803 and you got it. 30.87 = -866. To make it easier to not screw up with a negative symbol here or there you can run all the numbers in the positive and then just switch to negative at the end. It's calculating not interpolating but in some cases the answer choices are too close for interpolation.
Thanks for the interesting and easy to follow video. I have never seen a pressure altitude chart before as we don't use them in New Zealand. We also measure air pressure differently but once the pressure altitude is calculated how we get density altitude is the same. Looking at the latest weather briefing for my local airfield it is showing a temperature of 25°c and QNH 1006. I'm just glad I don't have to worry about converting °F to °C.
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I think it is the density of the air, it doesn't matter the gas as any gas can create lift (e.g. water vapour or N2/O2). Moist air is less dense than dry air because H2 in H20 has less molecular weight than O2 or N2 that makes up air. An engine needs O2 to breath, of course, so if O2 is displaced by any other gas that will degrade horsepower. I think ISA and calculations for density altitude assumes %RH is zero (zero water content). But moisture in the air can degrade performance due to reduced air density.
Mildly rusty private pilot here. I have a question about the formula you used. In your example, we are at sea level. If field elevation was significantly higher than sea level, would you adjust ISA TEMP with lapse rate before plugging it into the formula? Apologies if this is dumb.
Andrea Zaratin did you ever figure out the answer to your question? I'm having a hard time calculating the density altitude using the formula. I'm good with the e6b and chart but when I use the formula I come up with an answer that's a few hundred feet off. My field elevation is 858'.
I know it’s a year old comment but yes to answer your question you would adjust 2 degrees Celsius per 1000 feet of altitude. So if your field elevation is 5000 feet your ISA needs to be OAT - 5 degrees Celsius not 15 degrees.
@@mark4079 you need to know your temperature first. Then subtract that from the ISA and you get a number. Add your 858' to that number and you will get your density altitude.
Thanks!! This was really helpful. Do you have one for finding the Pressure altitude? I keep getting those questions on the practice tests and they stump me.
(Standard altitude - current altitude) * 1000 + Field elavation I hope you figured it out long before now but if anyone else clicks on your question this is for them too.
I am having trouble getting this formula to match what Foreflight reports for Density Altitude. I wonder if I am missing something else. My formula is as follows, (Pressure Altitude + Field Elevation)+(120*(OAT-Standard Day)). So for my local airport it's currently DA = (-119+710)+(120*(14-15)). Standard day would be sea level. -2 degrees per 1000 feet. Field elevation of 710 so .71*2 degrees = 1.42 off of the standard 15 degree day = 13.58. Therefore, 591+50.4=641.4'. Foreflight says 810'. Why don't these match up? Is Foreflight just building in a pad so people are more careful? Help!
I tried using this formula and was 1000 feet too low for a practice question in the Gleim test prep book. It gives 90 degrees F, 30.2" HG, and 4725 field elevation. The density altitude = pressure altitude + (120*(OAT-ST)) formula gives 6534.4 as the density altitude, but other calculators say 7400. Any ideas what I'm doing wrong? Numbers used: 4468 + (120 * (32.22 - 15))
Seems silly answering this after 3 years, but I just saw this now. You used 15 degrees C. That's the standard temp for sea level but you needed to use the standard temp for your pressure altitude. Would have been about 6.15 degrees for that PA. Ends up around 7,600 or so.
@@skyking2202 Completely forgot I ever left this comment, but thanks for the reply. Brings back memories. Now I answer these kinds of questions for a living.
Man you really got me messed up because you didn't say anything about lapse rates at standard temperature. People are probably using this formula without calculating the standard temperature at their given altitude. If you use 15 degrees for your equation when you're actually at 5000 feet you'll get the wrong answer.
Something I never understood is water displacing air. Yes, it affects the engine, but why is it so detrimental to the wings and lift? A hydrofoil wing or water wing would create more lift, ... Yes?
in the first example wouldnt you have gone to sea level but before going across to DA you would have added the 112ft and gone roughly one tenth above sea level before reading across?
Hi J Mason, yes that is correct. Thanks for clarifying! You can always use the formula as well and it will be more accurate than having to interpolate the chart. If you have any more questions feel free to reach out to our support team at support@mzeroa.com. Thanks for tuning in!
Jason, I like the idea using your math equasion because its pretty simple and I dont have to mess with graphs and charts. HOWEVER I cant seem to get the correct answer with it. For example one of the problems I was work on came out with a 1000' difference. I think its something that i'm overlooking. let me show you my work and maybe you can tell me the issue. RAW given data: Altimeter setting - 29.25 Temp= 81F (27C) Runway elevation = 5250' (altitude correction: 5250' + 626' which totals = 5875') the formula calculation. 5875 + [120 * (27c -15c)] 5875 + [120 * (12c)] solved parantheses first 5875 + [ 1440 ] solved bracket second 5875 + 1440 = 7315 Answer per formula 7315' Answer on the e6b and using the chart is 8500'. 🤔🤔🤔 I'm at a loss on how I'm messing up the math calculation,
Ok folks I got some clarification on the formula method. you have to use degrees fahrenheit. a quick background on this. I was frusterated when i tried to apply the math to the same problem with different numbers. heres the explanation I got back when I wrote in. Density Altitude Equation Raw Data Given: Altimeter setting - 29.25 Temp= 81F (27C) Runway elevation = 5250' The Math: Correction for elevation formula: Standard Pressure 29.92 - Given pressure 29.25 = 0.67 0.67 * 1000 = 670 (elevation correction in ft) 670 + runway elevation = 5920 Density Altitude correction formula: Corrected elevation of + [120 * (OAT Fahrenheit - Standard temp 59 degrees Fahrenheit)] 5920 + [120 * (81 - 59)] 5920 + [120 * (22)] solved internal parentheses first 5920 + [ 2640 ] solved bracket second 5920 + 2640 = 8560 Answer per formula 8560’
He is using the PA FACTOR FROM THE TABLE, this is my first try and rally was confused as he dont stata that we need use the Pa factor he use as Pa , from the table, 2 Differnt things
Great representation as always Jason. I was just wondering to go from the 25 Celsius marker then up to 112 feet instead of the sea level and then look up the chart in the left or the density altitude since the pressure altitude is 112 feet?
@ 7:05 Should I leave a heavy passenger or a light passenger behind. Should I leave a heavy bag or one light bag. behind.Question : where do you find how much weight is to be off loaded .
The question was for 29.80, but you changed it to 29.92, so I'm not sure how to solve my problem, I subtract 112 from? using chart? My problem is 30.30, 25 degrees F, Airport elevation at 3894. I see 30.30 is -348. So using chart, I take 3894 - 348 = 3546, cruise from 25 F up to 3546 then across to about 2100. The closet answer is 2200 so I choose that, but accuracy sucks! Your formula would be -348 + (120 X 4C? - 15C) = -348 + (120 X -11) = -348 + -(1320) = -1668? So confused!
Jason I watch Steveo, Baron Pilot and have seen several other RU-vid pilots and have never seen them use the calculator or calculate the formulas. Do you do the calculations after listening to AFIS and while the engine is warming up? When do you do this?
Hi Samuel! Use the formula: Density Altitude = Pressure Altitude + [120 x (OAT - ISA Temp)] If you need any further clarification please reach out to us at support@mzeroa.com. Hope this helps! Thanks for watching!
CFI here. I had to give you a thumbs down on this vid Jason. you make a statement that you are only affected by DA if you are in a non turbo charged aircraft. Although the engine, in a turbo charged aircraft, will be able to perform at sea level pressure, the prop and wing performance will still be reduced at high DA. you are not immune to DA because you have a turbo, you are simply improving one of three performance areas of the aircraft. the false sense of security of a turbo charger is also responsible for lives being lost.
Hi Allen, try to listen to the video once more. Jason says that airplanes with turbo charger or turbine engine(s) should not use the introduced DA rule of thumb. If you disagree, you are probably saying that such aircraft can in fact use the density altitude rule of thumb. For instance, does a turbine engine powered aircraft at standard sea-level pressure (29.92) and at 25 deg C feel the same, and thus climb the same, as at 15 deg C with approx. 1200 feet of pressure altitude? My guess would be that high temperature reduces performance more than low pressure. It is an interesting question though. Do you know the correct answer?
Even a turbo charged aircraft can use the DA rule of thumb. As DA increases, performance decreases. This is true for all aircraft but a turbo HELPS reduce the decrease in performance as DA increases. The wing and prop are still less efficient. You can help some with a constant speed prop and special wing designs, but thats all they do is HELP. None eliminate the effects. As for the question about the reduction in performance, temperature has a much longer arm on the performance factor (DA) of all aircraft. I could write a novel on the subject, but what it comes down to is hot air is less dense than cold air. The lower the density, the less air you have to create lift, thrust, and the further (runway length) you will need for takeoff and landing.
I'm just curious, turbocharged aircraft would have their own performance charts in the POH to aid pilots in making takeoff and landing decisions in higher DA wouldn't they?
I mean he did a great job explaining density altitude calculations which helped me out as a student pilot. One mistake about a somewhat unrelated subject shouldn’t warrant a thumbs down IMO
i got a question and idk how to google search it. i feel like i already know the answer, and that it's obvious BUT: at a high altitude, with your mixture leaned, i heard somewhere that when you do a go around or need power you should enrich the mixture to full. but that doesnt make sense to me at a high altitude. and idk why anyone would ever say to enrich the mixture, ever. i would assume to just get the engine set correctly for it's altitude and leave it. but i don't know for certain.
Hello! That could be correct depending on the conditions but it all depends. For a detailed answer from a CFI, please send us your question at support@mzeroa.com. Thanks for watching!
@@MzeroAFlightTraining im not a real pilot, i just play in the sim. so im not gonna do that, ill just assume i should keep my engine running healthy and not change it unless the engine wants me to. where im coming from is, i was sim flying in Colorado mountains, recreating a crash i saw on youtube, and the plane performed very poorly with full rich mix at that altitude in those situations. i died just like the real plane, N36JJ. but when i mixed it right, i barely survived (by like 20 feet) on the same course (might not technically be the same as the N36JJ flight, but close enough). in regards to that flight, i personally would have maintained a higher altitude earlier, but for the sake of recreation, i started from 10k feet and flew through the mountain passes and i can completely understand how that incident happened. flying through the mountains looks really scenic, feels neat, however they can get steep in a hurry.
I really like your presentations however, (please don't take this badly), bottom line--you talk too much! Do away with long pre explanations, just get to the point, show us how it's done and be finished. You continually go back and re-explain and re-explain. This is what my ground instructor did and I STRUGGLED to understand and stay awake during his presentations. Please take this as instructive, not destructive. Looking forward to more videos from you! Thank you!
Barry Schiff had a seminar at the AOPA fly in the other day and he cautions that the heat coming off the blacktop runway is higher than as reported in the atis.
i guess Im randomly asking but does anyone know of a method to get back into an instagram account..? I somehow lost my login password. I would appreciate any tips you can give me.
@Grey Malachi i really appreciate your reply. I got to the site through google and I'm trying it out now. Seems to take a while so I will get back to you later with my results.
Jason,Thx's for your recent reviews on both weight and balance and the most recent review on Density altitudes, i'm getting ready to take the written ground exam in the very near future, again I enjoy your videos on RU-vid, Keep up the good work,and I hope to see next Year at Fun n Sun or Oshkosh . Take Care
Man the always do simple problems I need something more complex like in the books because the test always has questions that are significantly more difficult
Isn’t PA separate from your actual physical height, and doesn’t that mean you wouldn’t know what’s standard temperature where you are when you use the chart and E6B.
Old video, but too many are being confused by saying that ISA is 15 degrees celsius. It is written in the video as DA = PA + (120 x (OAT - ISA TEMP)), but instead of saying "International Standard Atmosphere Temp" he says "Standard Temp." Yes, it is true that standard temperature at MSL will be 15 degrees celsius, but ISA implies that you are looking beyond MSL. You are supposed to subtract 2 degrees celsius every 1000 ft about sea level. ISA TEMP = 15 - (number of thousands of feet above MSL x 2). If you are are taking off from an airport at 2,000 ft, ISA TEMP is 15 - (2 x 2) = 11 DA = PA + (120 x (OAT - 11)) If you are taking off from an airport at 500 ft, ISA TEMP is 15 - (0.5 x 2) = 14 DA = PA + (120 x (OAT - 14)) Even at my own flight school there are numerous students and even instructors who always use 15 degrees celsius regardless of how high we are above sea level. For something as important as density altitude there needs to be better consensus across the board on how we calculate these things.
HELP! I must be missing something... I'm applying the formula to the following example and it doesn't match when I use the chart. Example Altitude = 5000ft Pressure = 30.10" Hg (chart factor of -165) PA = 4835ft Temp = 4C DA = 4835 + 120 x (4 - 15) = 4835 + 120 x (-11) = 4835 + (-1320) DA = 3515ft The chart shows approximately 4600ft. I'm new to this so I'm sure that I'm missing something obvious.
Hi JASON, just want to thank you for your outstanding instruction on RU-vid. Looking forward to signing up for your class. In one of your videos you talk about how to calculate density altitude. You say (density altitude equals pressure altitude + (120 X outside temperature minus standard temperature.) My problem and question is what if outside temperature is less than standard temperature? How are we going to subtract standard temperature?
Hey Derrick! You would subtract and therefore have a lower DA. If you get a negative number with that formula, you just add the negative which means subtract. If you need any further clarification on this please email us at support@mzeroa.com and we can have a CFI answer your question. Thanks for watching!
The calculator on my phone works it out for me even when the OAT is below 15°c. PA + ( 120 x ( OAT - 15 ) ) = DA if you are doing it manually I would go with a slight change to the formula PA - ( 120 x ( 15 - OAT ) ) = DA but that change around is not needed if you are typing it into a calculator where you can add the brackets.
I fly a Cessna 150 and I think about this a lot... How do I decide if the density altitude is a go/no go? I understand how to get the number, but how do I figure it is still safe or unsafe to fly in?
Cameron Tucker probably more about can you take off on the runway you have based on the calculations you find for DA and compare performance of your plane and takeoff distance.
That's what personal minimums are for. E.g. someone with little high altitude experience might want to have two or three times what the performance chart requires for conditions. After a few takeoffs that might get dialed back to a personal minimum of 1.5 times charted performance. For a given plane/field/load that might become a maximum temperature at which one will takeoff. It's all based on the POH performance data and your experience and currency though.
*I took my written test back in Feb, got a 85% and studied all on my own, mainly free using books from library etc! I made a video on it, but your videos Jason have helped me so much!! I'm taking my checkride this July 20th, thank you for all your help!!* :)
Love your videos. I'm just bobbing around The Bahamas for a few weeks, but as soon as I'm back, I'm going yo dedicate myself to plowing through to the commercial license. Hm, the electronic calculator is so much easier and quicker, but not many people talk about it. How come?
I found this video by accident, why this video is not on "remotepilot101.com" if as I know from other source this may be on 107 test + it explain the "density altitude" better?
Hello density apply to all types of propulsion including turbo charged engines so air density affects all aircraft performances fail to understand this will kill you it is that important. Saludos
In my area, a fellow who was a big time medicos, landed at a small high altitude airport in the mountains. The locals there had told him, "If you're going to takeoff, make sure that it's early in the morning when there's a little more substance to the air". This dude was overconfident, waited till a later in the day when the Summer heat began to thin the air out. He took off his little private plane from the little mountain airstrip, the plane could not old the altitude and ended up in a tree. Density altitude to me, in many forms, is vitally important. Thanks Jason
