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PPL Video Lectures (10 Jul 2020)

PPL Video Lectures covering Aerodynamics, General Knowledge, Performance, Meteorology And Navigation are now available through our website see front page for details.

× Welcome to the CPL Performance question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.

Pressure height

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MissSoph created the topic: Pressure height

Ok... I’m completely lost.... can someone help me out with this one.... and I’m sure I’m missing the bleeding obvious.... but I’ve been given
1760 AMSL for aerodromes elevation
QNH 1005
Temp 25 c
What is the pressure height....
The answer is 2000 to enter the landing weight chart :()
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  • John.Heddles
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  • ATPL/consulting aero engineer
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John.Heddles replied the topic: Pressure height

As for the other question -

(a) draw a picture - if you do this ALWAYS you will help yourself greatly.

(b) from the picture, the 1013 surface is below the MSL QNH surface.

How about you run the question and then post a scan of your answer for comment to get maximum value from the forum ? If you don't get 2000 ft for Hp, try again with the picture and keep doing it until it all falls into place for you.

Engineering specialist in aircraft performance and weight control.
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MissSoph replied the topic: Pressure height

Ummmm wowzers... I’m the fool.... I realised just what I was doing wrong....
So my equation was PH = ele + (qnh - 1013) x 30..... :() hmmmm...
I gave it another shot with the correct one this time.....
PH = ele + (1013-qnh) x30... ahhhhh... think it’s time to go to bed and get some rest ......
John.... you have the patience of a saint my friend.... I bet you were just shaking your head....
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  • John.Heddles
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John.Heddles replied the topic: Pressure height

I bet you were just shaking your head

Not at all, everyone takes a while to get their head around this flying stuff.

However, the comment about drawing a picture is really important. It is my conviction that a great many people try to use formulae without really understanding the derivation, limitations, etc. A picture usually makes everything a whole lot easier to follow (and not make simple formula mistakes).

Engineering specialist in aircraft performance and weight control.
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