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The density altitude/true air speed function is also accessed from NAV Menu 1.
Density altitude is the altitude at which your aircraft will perform depending on several
environmental conditions including air pressure and total air temperature (the tempera-
ture including the effect of speed), read on a standard outside temperature gauge on
most aircraft). True air speed considers the same factors.
To calculate the density altitude and true air speed:
1. Press
C
and rotate
O
to highlight ‘Dalt/tas?’.
2. Press
E
to access the density altitude page.
3. Using
K
and
O
, enter the indicated altitude (ialt) according to the aircraft instruments.
Press
E
.
4. Use
K
and
O
to enter the calibrated air speed (cas) according to the aircraft instruments.
Press
E
.
5. Use
K
and
O
to enter the barometric pressure (pres) obtained from ATC.
Press
E
.
6. Use
K
and
O
to enter the total air temperature (tat) according to aircraft instruments.
7. Press
E
and the density altitude and true air speed will be calculated and displayed.
8. Press
C
to remove the cursor.
The fuel planning page will display fuel requirements for both direct-to naviga-
tion and programmed routes. The planning function requires the pilot to know the
initial amount of fuel on board and the flow rate. You may also enter different ground
speeds to view various information based on different travel times, etc. If your instal-
lation has interfaced a fuel flow sensor to the GPS 155, the flow rate and other infor-
mation will be used from the sensor, and do not need to be entered manually.
14
NAV KEY
NAV Menu 1/Density Altitude
Density altitude & true air speed calculated.
Entering an indicated altitude.
155man (GOOD) 7/24/98 1:56 PM Page 14