0.00.138 PMDG 737NGX
TUTORIAL #2
27FEB15 RTM DO NOT DUPLICATE For Simulator Use Only
Enter these values into the RTE DATA page with the right side
LSKs. Notice that every waypoint below the one you just entered
inherits the wind data from above. This is useful when you have a
string of waypoints that all have the same or very similar winds. In
actual real life practice, the pilots will not enter a wind change
unless it is +/- 10 degrees or +/- 10 knots from the value that
preceded it in the list.
Press the illuminated EXEC button to commit the wind entries.
When I check the PROG page after doing this, it now shows 3.3
instead of 3.4 with the complex method vs. the simple one. It’s a
small difference, but a difference nonetheless. Multiply this out by
many hours on a long haul flight in a 777 and you could have a real
problem if you’d just used the simple way with the average.
Cruise temperature ISA deviation:
ISA stands for International Standard Atmosphere and is defined as a
pressure of 1013.25 hPa (29.92 inHg) and a temperature of +15C (+59F)
at sea level. This is where the standard altimeter setting we use above
transition altitude actually comes from.
The ISA deviation is how far away the actual temperature is on either side
of the expected standard temperature for the altitude we’re flying at.
There’s a simplified formula for calculating what the ISA temperature is for
the altitudes that airliners normally fly at – this is not 100% exact, but it’s
close enough for aviation purposes.
15C - (first two digits of the altitude x 2)
So for our cruise altitude of FL390 its:
15C - (39 / 2) = 15C – 78 = -63C
We’d be done here if our cruise altitude was below FL360, but
above FL360 a phenomenon known as the tropopause limits ISA
temp to -58.5C. The tropopause is a thermal boundary later
between the troposphere and the stratosphere.
Thus the ISA deviation is the actual air temperature minus the
ISA temperature for that altitude:
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