Hi everyone... met study and just wondering....pressure height can sometimes be referred to as pressure altitude? But then height is AGL , altitude is AMSL ..but pressure height talks about above sea level....am I just reading too much into it
Hi MISSOPH,
Pressure Height and Pressure Altitude are interchangeable terms - they refer to AMSL.
Cheers
SJM
[i][b]Pressure Height and Pressure Altitude are interchangeable terms - they refer to AMSL.[/b][/i]
'fraid that's not quite correct.
Pressure height (often written Hp) and pressure altitude are, indeed, equivalent terms for the same item. At least, I have never seen any authoritative claim that one differs from the other although I am quite happy to be proved wrong.
However, Hp is the altimeter reading in ISA above the assumed ISA SL datum for which the standard pressure is 1013.25 mb .. but let's just call it 1013 mb. It has naught, specifically, to do with AMSL. If the actual QNH happens to be 1013mb and the lapse rates happen to match ISA, then Hp will relate to AMSL on that occasion, coincidentally.
Useful monograph for some bedtime reading ... https://www.faasafety.gov/files/gslac/library/documents/2011/Aug/56396/FAA%20P-8740-02%20DensityAltitude%5Bhi-res%5D%20branded.pdf
Engineering specialist in aircraft performance and weight control.
I like to stress to classes that pressure height is a measure of pressure - not height. It is the height in ISA where the air has the same PRESSURE as the sample of air being considered.
The same applies to density height. It is a measure of density - not height.
Thanks Bob and John - my explanation was most incomplete (mobile devices!) and in context wrong. I meant to say was it's AMSL in the ISA model but really Bob's example gets right to the point - it a measure of pressure.
That was like a penny dropping Bob xox thank you so much ... the best explanation ...
