Question re QNH

[Walter Kranl]

Hi all,

Example:
airport elevation = 2,000 ft
QFE = 900 hPa
QNH = 900 + (2,000 / 27) = 974.07 hPa

How about high altitude airports like La Paz (13,323 ft elevation)?
I understand that QNH is an average value, but do you still calculate with 27 ft/hPa at this high altitude? I've read somewhere, that 27 ft/hPa is valid up to 10,000 ft (which corresponds to 700 hPA ISA). Which value do you use for airports higher than 10,000 ft to determine QNH?

Thank you
Walter

[simonijs]

Hi Walter,

This information is shown on the approach chart itself:

- on Aerosoft Charts it is shown in the middle just below the runway symbol as 382 hPa difference between QFE and QNH
- on Navigraph charts it is shown in the text information box on the top, showing 397 hPa difference (for the same runway  ).

It comes down to ± 33-34 ft per hPa as an average at this elevation.

Regards,
Simon

[Walter Kranl]

Thank you Simon!

Walter