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Instrument Flying Handbook
The Air Traffic Control System
Communication Equipment

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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

Communication Equipment

Navigation/Communication (NAV/COM) Equipment

Civilian pilots communicate with ATC on frequencies in
the very high frequency (VHF) range between 118.000 and
136.975 MHz. To derive full benefit from the ATC system,
radios capable of 25 kHz spacing are required (e.g., 134.500,
134.575, 134.600). If ATC assigns a frequency that cannot
be selected, ask for an alternative frequency.

Figure 9-1 illustrates a typical radio panel installation,
consisting of a communications transceiver on the left and a
navigational receiver on the right. Many radios allow the pilot
to have one or more frequencies stored in memory and one
frequency active for transmitting and receiving (called simplex
operation). It is possible to communicate with some automated
flight service stations (AFSS) by transmitting on 122.1 MHz

(selected on the communication radio) and receiving on a
VHF omnidirectional range (VOR) frequency (selected on
the navigation radio). This is called duplex operation.

An audio panel allows a pilot to adjust the volume of the
selected receiver(s) and to select the desired transmitter.
[Figure 9-2] The audio panel has two positions for receiver
selection, cabin speaker, and headphone (some units might
have a center "off" position). Use of a hand-held microphone
and the cabin speaker introduces the distraction of reaching
for and hanging up the microphone. A headset with a boom
microphone is recommended for clear communications. The
microphone should be positioned close to the lips to reduce
the possibility of ambient flight deck noise interfering with
transmissions to the controller. Headphones deliver the
received signal directly to the ears; therefore, ambient noise
does not interfere with the pilot's ability to understand the
transmission. [Figure 9-3]

Typical NAV/COM Installation.
Figure 9-1. Typical NAV/COM Installation.

Audio Panel.
Figure 9-2. Audio Panel.