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Virus SW 121
Pilot Operating Handbook
POH-121-00-40-001
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SECTION 1
GENERAL
1.7.2. METEOROLOGICAL TERMINOLOGY
IMC
Instrument Meteorological Conditions are meteorological conditions
expressed in terms of visibility, distance from cloud, and ceiling less
than the minima for visual flight defined in FAR 91.155.
ISA
International Standard Atmosphere (standard day) is an atmosphere
where
(1) the air is a dry perfect gas,
(2) the temperature at sea level is 15° C,
(3) the pressure at sea level is 1013.2 millibars (29.92 InHg), and
(4) the temperature gradient from sea level to the altitude at which the
temperature is -56.5° C is -0.00198° C per foot and zero above that
altitude.
MSL
Mean Sea Level is the average height of the surface of the sea for all
stages of tide. In this Handbook, altitude given as MSL is the altitude
above the mean sea level. It is the altitude read from the altimeter when
the altimeter’s barometric adjustment has been set to the altimeter
setting obtained from ground meteorological sources.
OAT
Outside Air Temperature is the free air static temperature obtained from
inflight temperature indications or from ground meteorological sources.
It is expressed in either degrees Celsius or degrees Fahrenheit.
-
Pressure Altitude is the altitude read from the altimeter when the
altimeter’s barometric adjustment has been set to 1013 mb (29.92 inHg)
corrected for position and instrument error. In this Handbook, altimeter
instrument errors are assumed to be zero.
-
Standard Temperature is the temperature that would be found at a
given pressure altitude in the standard atmosphere. It is 15° C at sea
level pressure altitude and decreases approx. 2° C for each 1000 feet of
altitude increase.
DA
Density Altitude (ft) is pressure altitude corrected for non-standard tem-
perature. As temperature and altitude increase, air density decreases.
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General