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Instrument Flying Handbook
Flight Instruments
Dynamic Pressure Type Instrument

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Instrument Flying


Table of Contents

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

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

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

true airspeed indicator
Figure 3-12. A true airspeed indicator allows the pilot to correct
IAS for nonstandard temperature and pressure.

Mach Number
As an aircraft approaches the speed of sound, the air flowing
over certain areas of its surface speeds up until it reaches the
speed of sound, and shock waves form. The IAS at which
these conditions occur changes with temperature. Therefore,
in this case, airspeed is not entirely adequate to warn the
pilot of the impending problems. Mach number is more
useful. Mach number is the ratio of the TAS of the aircraft
to the speed of sound in the same atmospheric conditions.
An aircraft flying at the speed of sound is flying at Mach
1.0. Some older mechanical Machmeters not driven from
an air data computer use an altitude aneroid inside the
instrument that converts pitot-static pressure into Mach
number. These systems assume that the temperature at any
altitude is standard; therefore, the indicated Mach number is
inaccurate whenever the temperature deviates from standard.
These systems are called indicated Machmeters. Modern
electronic Machmeters use information from an air data
computer system to correct for temperature errors, These
systems display true Mach number.

Figure 3-13. A Machmeter shows the ratio of the speed of sound to
the IAS the aircraft is flying.

Most high-speed aircraft are limited to a maximum Mach
number at which they can fly. This is shown on a Machmeter
as a decimal fraction. [Figure 3-13] For example, if the
Machmeter indicates .83 and the aircraft is flying at 30,000
feet where the speed of sound under standard conditions is
589.5 knots, the airspeed is 489.3 knots. The speed of sound
varies with the air temperature. If the aircraft were flying at
Mach .83 at 10,000 feet where the air is much warmer, its
airspeed would he 530 knots.

Maximum Allowable Airspeed
Some aircraft that fly at high subsonic speeds are equipped
with maximum allowable ASIs like the one in Figure 3-14.
This instrument looks much like a standard air-speed indicator,
calibrated in knots, but has an additional pointer colored red,
checkered, or striped. The maximum airspeed pointer is
actuated by an aneroid, or altimeter mechanism, that moves
it to a lower value as air density decreases. By keeping the
airspeed pointer at a lower value than the maximum pointer,
the pilot avoids the onset of transonic shock waves.

maximum allowable airspeed indicator
Figure 3-14. A maximum allowable airspeed indicator has a
movable painter that indicates the never-exceed speed, which
changes with altitude to avoid the onset of transonic shock waves.

Airspeed Color Codes
The dial of an ASI is color coded to alert the pilot, at a
glance, of the significance of the speed at which the aircraft
is flying. These colors and their associated airspeeds are
shown in Figure 3-15.

The Earth is a huge magnet, spinning in space, surrounded
by a magnetic field made up of invisible lines of flux. These
lines leave the surface at the magnetic north pole and reenter
at the magnetic South Pole.

Lines of magnetic flux have two important characteristics:
any magnet that is free to rotate will align with them, and
an electrical current is induced into any conductor that cuts
across them. Most direction indicators installed in aircraft
make use of one of these two characteristics.