Appendix

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Deutsch
Approaching Quito – Historic Procedures
Aerosoft GmbH 2016
Appendix: High Density Altitude
If there is one thing that makes this product special it is the high altitude
of the airports. It is our experience that many sim pilots do not fully un-
derstand the effects of the resulting lower air pressure, so a full chapter
on flying in these conditions is in order.
High Density Altitude
In this chapter we are going to use the Cessna 182RG as our base
model, for all other aircraft the principle is the same, only the numbers
change. There is one complete factor that should be used when talking
about Density Altitude that we will not mention, Humidity. It is not a
major factor and in FS it is not used. If you want to know, high humidity
will RAISE the Density Altitude.
IMPORTANT: The ACTUAL altitude of an airport is of little or no con-
sequence, the only thing that matters is the DENSITY ALTITUDE of the
airport. The only thing that matters is the AMOUNT of air molecules!
Air is needed for many things (we will use the word ‘air’ to describe the
mixture of gasses we experience):
• to create lift
• to create a forwards force by pushing onto (jets) or ‘screwing’ into
(props)
• to assist the combustion of the fuel
• to cool the propulsion system
• and of course, the pilot also needs something to breath.
If there is less air all of these things will not be as efficient as in optimal
conditions. So what effect has that one to the performance of the air-
craft? And in particular for the take-off and landing? Well how does a
takeoff run of 1800 feet sound to you? For a Cessna that is not loaded
very heavy? Is that impressive or not? Look at the following table that
shows the relation between altitude, temperature and pressure. The
data for takeoff and landing are for a moderately loaded Cessna 182 RG.
Altitude
in feet
Tempe-
rature in
degrees F
Altimeter
Setting in
Inch Hg
Resulting
Density
Altitude
Required
Runway
Takeoff
Required
Runway
Lading
0 59 29.291 0 ft 640 ft 600 ft
4000 59 29.291 4924 ft 950 ft 720 ft
8000 59 29.291 9816 ft 1350 ft 900 ft
8000 100 29.00 13255 ft 1850 ft ? 1200 ft
Where there are question marks they are there because the Cessna ma-
nual does not supply these numbers and they have been extrapolated
from the other numbers. Keep in mind that a turbo charged aircraft like
the 182 is built to operate at higher altitudes and that it will perform
much better than a non turbo charged aircraft.
If you try to take off with a Piper Cub with a density altitude of 1300’
you’ll probably never reach takeoff speed before running out of runway
and landings will have to be done at speeds ABOVE cruise speed. In the
last row of the example the aircraft is located at 8000’ feet but for all
logical and practical purposes it is 5000’ higher.
Density Altitude is the altitude where the aircraft THINKS it is.
Also it is not only performance that suffers; your engine will also over-
heat MUCH faster because there is less air to cool the engine. And
when the winter comes and density altitude becomes less of an issue
you run into another problem. It’s very easy to run into very cold layers
of air only minutes after takeoff and icing is a real danger. One thing
to keep in mind… your air speed indicator is always corrected for the
density altitude, it shows what it feels.
High (Density) Altitude Operations
Flying from high altitude airports is something that is inherently more
dangerous than flying from airports located nearer to sea level. But the
major issue is that it is different and that the problems escalate much
faster into real dangers.