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Pilot's Handbook of Aeronautical Knowledge
Aircraft Performance
Density Altitude

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




Air density is affected by changes in altitude, temperature,
and humidity. High density altitude refers to thin air while
low density altitude refers to dense air. The conditions that
result in a high density altitude are high elevations, low
atmospheric pressures, high temperatures, high humidity, or
some combination of these factors. Lower elevations, high
atmospheric pressure, low temperatures, and low humidity
are more indicative of low density altitude.

Using a flight computer, density altitude can be computed
by inputting the pressure altitude and outside air temperature
at flight level. Density altitude can also be determined by
referring to the table and chart in Figures 10-3 and 10-4.

Field elevation versus pressure.

Figure 10-3. Field elevation versus pressure. The aircraft is located
on a field which happens to be at sea level. Set the altimeter to the
current altimeter setting (29.7). The difference of 205 feet is added
to the elevation or a PA of 205 feet.

Density altitude chart.
Figure 10-4. Density altitude chart.

Effects of Pressure on Density
Since air is a gas, it can be compressed or expanded. When
air is compressed, a greater amount of air can occupy a
given volume. Conversely, when pressure on a given volume
of air is decreased, the air expands and occupies a greater
space. That is, the original column of air at a lower pressure
contains a smaller mass of air. In other words, the density is
decreased. In fact, density is directly proportional to pressure.
If the pressure is doubled, the density is doubled, and if the
pressure is lowered, so is the density. This statement is true
only at a constant temperature.