QEV 001 Pressure & True Altitude (A)

How to convert from Pressure Altitude to True Altitude.
Google 'Cat3C i Books' for hundreds of practice questions with explanations and diagrams.
*Please note that there is a written error on the whiteboard at 4 mins 43 seconds - I state "993 hectopascals" but write "933 hectopascals". My apologies for this mistake!

[@1WALTERNOTHLING]

6 steps and you have it, thank you very much for posting this! Quick and easy, explained every step!

[@Mike-cx5dn]

You are a saint!!! The best teacher I have ever seen!! Wish you were my ATPL teacher! Good bless you

[@Cat3CATPLTraining]

Thank you Mike, for your very kind words, although I'm not sure than canonization would be appropriate. Saying that, the idea does appeal, but on the condition I become the first living saint.

[@nunofrg]

outstanding teacher, wished my teacher was as good as you. thank you very much!

[@Cat3CATPLTraining]

Thank you for your kind words. :-)

[@ahmadtheaviationlover1937]

All pilots are natural born teachers and that pilots are awesome kinds of people

[@taffpike4277]

'Above sea level' is the same as above mean sea level and simply means that, the aircraft is 9,999 feet above mean sea level (amsl). Mean sea level (MSL) is the AVERAGE sea level datum, on an Earth where the sea does not suffer from mechanical or gravitational effects, from which all elevations of terrain and obstacles are measured. It is the point for determination of QNH, from which indicated altitude above mean sea level is measured, and displayed on an altimeter with QNH set in the altimeter sub-scale. The WGS 84 ellipsoid is the international standard ellipsoid used for charts and for GPS positions, and defines mean sea level.

[@anthonymacle1880]

The way EASA wants us to calculate this: 1/ 15,000-1660= 13,340. **FIRST** we are going to apply the tempearture deviation to 13,340ft (Parcel of air under the aircraft, we cannot measure the correction in the area occupied by the terrain: 1660ft). 2/ If we do 13,34 X4X 15=800ft. When the temperature is lower then our True altitude is also lower. 3/ Now we do 15,000 - 800 = 14,200ft and this is our TRUE ALTITUDE MSL **In the question they are using the term "FL150", FL= QNE . Above Transition level we use QNE / Standard Pressure 1013.** 4/ Last thing we need to do is to correct for the pressure. 1013-993= 20hpa. So far EASA has given 27ft/hpa to calculate the correction. 20X27= 540ft. **Why do you need to do that ? You are above the transition level so your altimeter is set to STD 1013. You know that the QNH is lower so again you will have to remove the value found to obtain your TRUE ALTITUDE** 5/ 14,200 - 540 = 13,660ft is your final result. Would you agree Tony ? And by the way thank you for your great videos they are very helpful and very well explained =)

[@Cat3CATPLTraining]

Correct. The airspace between QFE and QNH datums is assumed to be ISA (that is how QNH is calculated and how the barometric altimeter measures altitude) - this is why the altimeter is always correct at the aerodrome datum. This is laid out in ICAO Doc.8168. I have been informed that both MET and FPL will be adopting this (correct method) under the new EASA Learning Objectives.

[@salahalobaidi3029]

thank you are best no need go round and round and the result is same not about, about mack confusion . pls can you send me more thinks for calculating

[@taffpike4277]

The question states 993 not 933. 933 is my typo when writing the solution, which wasn't noticed until after the event, when the videos had been produced. Good luck with a QNH of 933 - that's very near to the UK low record of 925.6, and that was probably not a nice day! There was a day not too many years ago in Belfast (Aldergrove) where the QFE was off the altimeter.

[@AndrewMick97]

Actually the best explanation out there, thanks

[@taffpike4277]

Thank you AM, try out my explanations at my question bank: atplontrack.com - I am adding video explanations as I can. I also offer 1-2-1 and group GNAV training in person and online

[@sklajban]

Wunderful! Thank you for the explanation!

[@taffpike4277]

It won't be as accurate but you could use the altitude above mean sea level, provided the ground elevation isn't too high. The higher the ground elevation, the less accurate the true altitude. These calculations are no longer required in EASA and UK CAA General Navigation; they are now in Meteorology and Flight Planning, but I can't speak for other authorities.

[@manojmohan7264]

cannot believe the number of times ive come to this video over the years

[@taffpike4277]

You can only work with the information you have. No station elevation - you have to take the conversion down to sea level...unless they give you the QFE as well as the QNH, in which case you should be able to work out the station elevation. (QNH - QFE) x 30

[@LuisPerez-qj6mj]

Thanks for the explanation! I have another question, why did you calculate the temperature that should be at 15.000ft PA and not at 14.400 to calculate the ISA deviation?

[@taffpike4277]

@@LuisPerez-qj6mj ISA pressure altitude - ISA temperature

[@yooo7774]

Thank you 🙏 and you only have 2 min to calculate it on your written test

[@pilotactor777]

excellent explanation-clear and concise

[@ОлегАндрианов-и6ч]

Hi, Tony. In this video to calculate temp correction you apply indicated altitude: AGL=Indicated Alt-elevation (14400'-1660'=12740'), but in the video, where you had to find the approximate indicated altitude to clear the obsticle you apply true alt: AGL=True Alt-elevation (11800-6200=5600). Could you explain?

[@zaurvaliyev65]

Thank you very much. Very clear. Well done man. You’re genius 😎😅 👍🏼

[@1p2a3d4d5y]

Excellent, clear and thorough!

[@hanookgill4471]

Well explained and easy to follow thank you very much!

[@alkancelik]

İ have learn a lot of things by you thank you for teaching

[@Cat3CATPLTraining]

+Ahmet A. Celik My pleasure Ahmet :-)

[@lyliedavid7547]

Excellent explanation

[@alkancelik]

if you look 4.43second the table is writing That 933

[@Cat3CATPLTraining]

+Ahmet A. Celik Good grief! You are absolutely correct! Nobody has spotted that before, myself included!! Well done and thank you....we will have to live with it though! I have added a comment to the title page.

[@christosmichos9932]

Very informative ! Thank you very much

[@tsehayenegash8394]

best video. How can I convert 10 hPa into km?

[@edgarxavier493]

Hi good explanation. So does this mean that MSL (mean sea level) and ASL (above sea level) are 2 different things..

[@hmabboud]

Thank you!

[@Grumpy412-rc7hb]

How to get TEC without ground elevation

[@taffpike4277]

Go to atplontrack.com and see my other GNAV and other explanations. I will be adding more videos to atplontrack.com in the very near future.

[@johnpro2847]

@ 04:32 I did not notice the error until Ahmet pointed it out. 933 less 1013 should be -80

[@doo_9536]

it's a mistake, QNH was 993. you can see on graphic

[@chevra100]

Really good videos! Thank you so much!! :-)

[@alkancelik]

ı domt understand that how you calculate the (993-1013)=-20 the calculation is -80?

[@Cat3CATPLTraining]

+Ahmet A. Celik Enter into a scientific calculator: 993 - 1013 = The answer is definitely -20 I cannot see where you are getting -80 from. Please explain.

[@edgarxavier493]

Shouldn't the pressure correction be +600 ft. 1013-993 = 20. Then 20*30 = 600ft.

[@taffpike4277]

If you are converting from a pressure altitude to an indicated altitude amsl, and the QNH < 1013 hPa, you SUBTRACT the pressure correction. If you note, I use (QNH - 1013) x 30 ft, which, when converting from pressure altitude to an indicated altitude amsl always provides the pressure correction in the correct sense. Then use "Indicated altitude amsl = pressure altitude + pressure correction" and a negative pressure correction provides "Indicated altitude amsl = 15,000 ft - 600 ft". It is not the only way to do these type of problems, it is just one method I have found very useful, especially for students who can only follow rigid formulas and have problems thinking 'outside the box'.

[@javi.i7i505]

you are the best

[@anthonypike277]

Why would you want to convert 10 hPa into kilometres? 10 hPa = 300 feet = approximately 100 metres = 0.1 kilometres. Seems a bit pointless.

[@basitsyed1720]

From where did you get 4 per 1000ft? Is not 1.98 per 1000ft?? Correct me if I’m wrong, Thanks!!

[@taffpike4277]

You are confusing the ISA temperature lapse rate of 1.98 /1,000 ft (approximated to 2 / 1,000 ft) with a 'constant' in a formula for calculating a difference in a measurement of altitude. You should discuss this with your ATO instructor.

[@basitsyed1720]

CAT 3C got it you’re absolutely right Thanks for quick reply

[@ОлегАндрианов-и6ч]

I mean, can we neglect this difference?

[@alkancelik]

im sorry for That in the White board you Write 933 so ı calculate it 1013-933 =-80 but in the question its writing Qnh 993 thank you for help us ı see it wrong

[@surbhipandya7429]

What if elivation is not given???

[@MohammedPersonne]

Brilliant!

[@nickde6339]

why would you even bother doing all that math when you know the QNH you are given is about half an inch lower in mercury (29.32inHg) compared to the standard 29.92inHg, how much do you need here to get from 29.32 to 29.92?? yes, 60.. then translate that into the hundreds, 600 feet.... you dont have to make stuff harder. I mean, if im getting this correctly, youre PHYSICALLY at 15k feet above sea level, but because the pressure is lower than standard, the aircraft feels like its still at 15k but in a lower pressure mass of air which is 14,400. So Im gonna guess the absolute altitude (AGL) is actually 15k - 1660k. 14,400k - 1660k would be the absolute altitude with pressure correction. (provided that the altimeter is set to standard and not the airfields QNH)

[@nickde6339]

what a joke, you dont even get -20 if you subtract 1013 off 933 and then multiply the result by 30. You get -2,400. Dont get this methodology.

[@casst346]

where did you get 993 hp for sea level? i thought standard sea level was 1013 hp...i thought the standard sea level pressure is 1013hp...or 29.92 hg

[@taffpike4277]

1013 hPa is the International Standard Atmosphere (ISA) standard pressure datum. 993 hPa is the QNH, which is QFE reduced to sea level, using ISA as the conversion factor (30 ft per 1 hPa approx.). The first conversion is from the pressure altitude (based on 1013) to the indicated altitude amsl (based on QNH).

[@nickde6339]

you will often get a lower or higher QNH, the standard is just the standard. it doesnt mean it always has to be like that. Winds change affecting pressure levels, temp changes etc..moisture

[@casst346]

@@nickde6339 ok..is the standard used when establishing flight levels?

[@Eat_delisious]

4:32 You said 993 but wrote 933-1012= 20. I got confused.

[@taffpike4277]

But you managed to figure it out, didn't you?

[@Eat_delisious]

I did, thank you so much for this video.

[@fatimashk6237]

Bro invented the term *complication*

[@Yannick3585]

*1.98 °C per 1000 feet

[@rashid37009]

Don't tell me. I can't learn it in years 😕 😪

[@kamilhaadyn8444]

Teach me master