Flytec 6020 * - Manual (Page 12)

Operating Manual Flytec 6020
2 Display Screens
2.1 Altimeter and air pressure
A barometric altimeter calculates altitude from the present air pressure of the atmosphere.
Air pressure will decrease at increasing height. Due to the fact that air may be compressed,
the pressure decrease is not linear, but indeed exponential. The basis for altitude calculation
in aviation is an international formula which defines a standard atmosphere.
In the CINA- Standard atmosphere the basic pressure on sea level is 1013,25 hPa
(Hektopascal) at a temperature of 15°C. Furthermore it defines a continuous temperature
decrease at increasing height of 0,65°C per 100m ascent. Therefore is binding: a barometric
aviation altimeter displays the precise altitude only if weather conditions are in exact
accordance to the standard atmosphere. In practice, such analogy is more likely to be the
exception!
Air weight and pressure are strongly influenced by air temperature. If temperature deviates
from standard atmosphere, the display of altitude calculated as per the international formula
is no longer correct. The altimeter displays during summer, when temperatures are higher,
indeed altitude parameters which are too low, and during the winter it is exactly the contrary!
Flying at lower temperatures is effectively done at lower altitude, and at higher temperatures
flight altitude is higher than the altimeter displays! The deviation of 1 °C per 1000 height
meters induces approx. 4 m error. (This empirical formula is valid for up to 4000m!)
If you fly during summer through 2000 height meters in an air mass being too warm by 16 °C
compared to standard atmosphere, the altimeter will then display 2 x 4 x 16 = 128m
difference in altitude under real height! Based upon the internationally determined altitude
calculation with standard values, this display error caused by air temperature shall not be
rectified by the instrument.
Air pressure changes in relation to weather conditions. In order to compensate for display
fluctuations, an altimeter always needs to be gauged. This means that the altimeter has to
be set precisely before take-off for any flight to a well-known altitude value. Caution:
the atmospheric pressure may change during the timeline of one day up to five Hektopascal
(for ex. cold front). As a result this is after all the equivalent of more than 40 meters height
difference.
There is another possibility to gauge the altimeter which is to enter the current QNH pressure
value. The QNH (Question Normal Height) applied in aviation matches the current local
air pressure, as it would be at sea level, so that the altimeter would indeed display 0m.
Due to this process the local pressure data recorded by the various measurement stations
is area-wide comparable, irrespective of the geographical height.
The QNH-value is subject to be continuously updated and may be read in the flight weather
report, or required by radio from airfields, or by enquiry on the Internet.
The instrument provides 3 altitude displays.
2.1.1 Altimeter A1, absolute Altitude
A1 is always the altitude above sea level (large display in upper part of display screen).
Altitude A1 is originally set by the manufacturer to show the correct altitude of user’s
location if air pressure at sea level is 1013 hPa. Bearing in mind that this only happens
infrequently, the displayed altitude A1 should be gauged before each take-off to the actual,
true height at location.
Correction of altitude A1:
Long pressure on
F1
⇒ will generate the message Mod Alt1 ↑↓ in the lower information line.
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