QNH pressure calculation (ICAO Doc 9837, second edition – 2011) - AWS810

AWS810 System Description
Document code
M212417EN
Revision
H
ft:locale
en-US
Product
AWS810
Document type
Technical description

QNH, the pressure reduced to mean sea level according to ICAO standard atmosphere, is calculated with the following formulas:

  1. First, the elevation of pressure QFE in International Standard Atmosphere (ISA) is calculated with the following formula:

    H I S A = 44330.77 − 11880.32 * Q F E 0.190263

  2. Then, QNH of the elevation difference is calculated with the following formula:

    Q N H = 1013.25 * ( 1 − 0.0065 * H I S A − H 288.15 ) 5.25588
Explanation of QNH pressure (ICAO Doc 9837, second edition – 2011) calculation formula
Item Explanation
HISA Elevation of pressure QFE in International Standard Atmosphere (ISA)
QNH Sea level pressure [hPa]
QFE Station level air pressure [hPa]
H Station altitude
Inputs for QNH (ICAO Doc 9837, second edition – 2011) pressure calculation
Input Variable
Atmospheric pressure (PA) (QFE) QFEAVG1M (average 1‑minute QFE pressure)