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The density altitude/true airspeed function is also accessed from NAV Menu 1.
Density altitude is the theoretical altitude at which your aircraft will perform depending
on several environmental conditions, including air pressure and total air temperature
(the temperature including the heating effect of speed, read on a standard outside tem-
perature gauge on most aircraft). True airspeed considers the same factors.
To calculate the density altitude and true air speed:
1. Press
N
and rotate
O
until NAV Menu 1 is displayed.
2. Press
C
twice and rotate
O
to highlight ‘Dalt/tas?’.
3. Press
E
to access the density altitude page.
4. Use
K
and
O
to enter the indicated altitude (‘ialt’) and press
E
.
5. Use
K
and
O
to enter the calibrated airspeed (‘cas’). Press
E
.
6. Use
K
and
O
to enter the air pressure (‘pres’) and press
E
.
7. Use
K
and
O
to enter the total air temperature (‘tat’).
8. Press
E
and the density altitude and true airspeed will be calculated and displayed.
9. Press
C
to remove the cursor.
If your installation includes components to provide any of the information
required on the density altitude page, they will be used as the defaults.
The fuel planning page will display fuel requirements for both direct-to naviga-
tion and programmed routes. The fuel planning function requires the pilot to enter
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. If your
installation is interfaced to a fuel flow sensor, the flow rate and other information will
be supplied by the fuel flow sensor.
24
Fuel planning page showing calculation from pre-
sent position to ‘KDAL’.
Density altitude/true airspeed page
SECTION
1
NAV KEY
Density Altitude &
True Airspeed
250xl manual 2 7/17/98 1:27 PM Page 24