Extra EA 400 - Meteorological Terminology

Section 1 Pilot’s Operating Handbook
General EXTRA 500
1.5.b Meteorological Terminology
ISA International Standard Atmosphere in which
a The air is a dry perfect gas;
b The temperature at sea level is 15° Celsius (59° Fahrenheit);
c The pressure at sea level is 1013.2 mbar (29.92 inches hg.);
d The temperature gradient from sea level to the altitude at which
the temperature is -56.5°C (-69.7°F) is -1.98°C (-3.564°F) per
1,000 foot and zero above that altitude.
OAT Outside Air Temperature is the free air static temperature,
obtained either from inflight temperature indications or ground
meteorological sources, adjusted for instrument error an
d
compressibility effects.
Indicated
Pressure
Altitude
The number actually read from an altimeter when the
barometric subscale has been set to 1013.2 mbar (29.92 in. hg.).
Pressure
Altitude
Altitude measured from standard sea level pressure
(1013.2 mbar/29.92 0n. hg.) by a pressure or barometric
altimeter. It is the indicated pressure altitude corrected fo
r
p
osition and instrument error. In this Handbook, altimete
r
instrument errors are assumed to be zero.
Station
Pressure
Actual atmospheric pressure at field elevation.
Wind The wind velocities recorded as variables on the charts of this
Handbook are to be understood as the headwind or tailwin
d
components of the reported winds.
1-14 26. January 2011