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18
Using the Altitude and Speed
Correction Windows
Altimeters and airspeed indicators are designed to
give correct indications under standard conditions
at sea level. The consistency of the earth’s atmo-
sphere does not change linearly as you gain alti-
tude; its density is affected by variations in tempera-
ture and pressure. The E6-B provides windows on
the slide rule side so you can allow for these
variations when converting calibrated airspeed to
true airspeed or indicated altitude to true altitude.
True Airspeed and Density Altitude
Note that the outer scale of your flight computer is
marked TAS (true airspeed) and the middle scale is
marked CAS (calibrated airspeed).
The Approved Flight Manual for your airplane
contains a conversion table that allows you to
convert indicated airspeed to CAS. The difference
is greatest at low speeds and becomes negligible at
cruise speeds. To determine true airspeed you
must first know the pressure altitude. Set your
altimeter to 29.92 and read the altitude indicated;
that is the pressure altitude. Note the outside air
temperature and convert it to Celsius using the
conversion scale at the bottom of the flight computer.
1. Set the pressure altitude in the window oppo-
site the outside air temperature in Celsius.
2. Without moving the computer’s scales, read
the true airspeed on the outer scale opposite
CAS on the middle scale.