MicroStep-MIS MSB780X1D - Page 55

MSB780(X) - User’s Guide
Table 15: Valid ranges for HQNH parameter
Valid ranges for HQNH parameter
Unit Minimum Maximum
m -30 5000
ft -99 16000
where
h
QNH
is station elevation in m
g is gravitational acceleration 9.81 m.s
−2
R is gas constant 287 J.kg
−1
K
−1
T is standard temperature 288.15 K
α is standard temperature lapse rate -0.0065 K.m
−1
or (if ICAO mode turned on)
QNH = p
0
·

1 + β ·
H − H
QNH
T

−g
β·R
(12)
where
H =
−T
β
− 11880.32 · QF E
0.190263
(13)
H
QNH
=
r · h
QNH
r + h
QNH
(14)
p
0
is "standard" pressure 1013.25 hPa
β is atmospheric temperature lapse rate -0.0065 K.m
−1
H is equivalent altitude in ICAO standard atmosphere
T is standard temperature 288.15 K
g is gravitational acceleration 9.80665 m.s
−2
H
QNH
(capital letter) is geopotential official aerodrome elevation
h
QNH
(small letter) is geometric (not geopotential) official aerodrome elevation
r is earth radius 6356766 m
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