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Instrument Flying Handbook
Aerodynamic Factors
Atmosphere

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Instrument Flying
Handbook

Preface

Table of Contents

Chapter 1. Human Factors
Chapter 2. Aerodynamic Factors
Chapter 3. Flight Instruments
Chapter 4. Section I
Airplane Attitude Instrument
Flying
Using Analog Instrumentation
Chapter 4. Section II
Airplane Attitude Instrument
Flying
Using an Electronic Flight
Display

Chapter 5. Section I
Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Chapter 5. Section II
Airplane Basic
Flight Maneuvers
Using an Electronic Flight
Display

Chapter 6. Helicopter
Attitude Instrument Flying

Chapter 7. Navigation Systems
Chapter 8. The National
Airspace System

Chapter 9. The Air Traffic
Control System

Chapter 10. IFR Flight
Chapter 11. Emergency
Operations

Newton’s Second Law of Motion.: the Law of Momentum.
Figure 2-5. Newton's Second Law of Motion.: the Law of
Momentum.

Air density is a result of the relationship between temperature
and pressure. Air density is inversely related to temperature
and directly related to pressure. For a constant pressure to be
maintained as temperature increases, density must decrease,
and vice versa. For a constant temperature to be maintained
as pressure increases, density must increase, and vice versa,
These relationships provide a basis for understanding
instrument indications and aircraft performance.

Layers of the Atmosphere
There are several layers to the atmosphere with the
troposphere being closest to the Earth's surface extending to
about 60,000 feet at the equator. Following is the stratosphere,
mesosphere, ionosphere, thermosphere, and finally the
exosphere. The tropopause is the thin layer between the
tropospheric and the stratosphere. it varies in both thickness
and altitude hut is generally defined where the standard
lapse (generally accepted at 2° C per 1,000 feet) decreases
significantly (usually down to 1° C or less)

International Standard Atmosphere (ISA)
The International Civil Aviation Organization (ICAO)
established the ICAO Standard Atmosphere as a way
of creating an international standard for reference and
performance computations. Instrument indications and
aircraft performance specifications are derived using this
standard as a reference. Because the standard atmosphere is
a derived set of conditions that rarely exist in reality, pilots
need to understand how deviations from the standard affect
both instrument indications and aircraft performance,

in the standard atmosphere, sea level pressure is 29.92" inches
of mercury (Hg) and the temperature is 15° C (59° F). The
standard lapse rate for pressure is approximately a 1" Fig
decrease per 1,000 feet increase in altitude. The standard lapse
rate for temperature is a 2° C (3.6° F) decrease per 1,000 feet
increase, up to the top of the stratosphere. Since all aircraft
performance is compared and evaluated in the environment

 

Newton’s Third Law of Lint/ca: the Low of Reaction.
Figure 2-6. Newton's Third Law of Reaction: the Low of Reaction.
 

of the standard atmosphere, all aircraft performance
instrumentation is calibrated for the standard atmosphere.
Because the actual operating conditions rarely, if ever, fit: the
standard atmosphere, certain corrections must apply to the
instrumentation and aircraft performance. For instance, at
10,000 ISA predicts that the air pressure should he 19.92' Hg
(29.92" - 10' Hg = 19.92") and the outside temperature at -5°C
(15° C - 20° C). If the temperature or the pressure is different
than the International Standard Atmosphere (ISA) prediction
at) adjustment must be made to performance predictions and
various instrument indications.

Pressure Altitude
There are two measurements of the atmosphere that affect
performance and instrument calibrations: pressure altitude
and density altitude. Pressure altitude is the height above the
standard datum pressure (SD?) (29.92" Fig, sea level under
ISA) and is used for standardizing altitudes for flight levels
(FL). Generally, flight levels are at or above 18,000 feet
(FL 180), providing the pressure is at or above 29.92"Hg.
For calculations involving aircraft performance when the
altimeter is set for 29.92" Hg, the altitude indicated is the
pressure altitude.

Density Altitude
Density altitude is pressure altitude corrected for nonstandard
temperatures, and is used for determining aerodynamic
performance in the nonstandard atmosphere. Density altitude
increases as the density decreases. Since density varies
directly with pressure, and inversely with temperature, a
wide range of temperatures may exist with a given pressure
altitude, which allows the density to vary. However, a
known density occurs for any one temperature and pressure
altitude combination. The density of the air has a significant
effect on aircraft and engine performance. Regardless of the
actual altitude above sea level an aircraft is operating at, its
performance will be as though it were operating at an altitude
equal to the existing density altitude.

 

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