| Home | Privacy | Contact |

Instrument Flying Handbook
The Air Traffic Control System
Communication Equipment

| First | Previous | Next | Last |

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

Boom Microphone Headset, and Push-To Talk Switch.
Figure 9-3. Boom Microphone Headset, and Push-To Talk Switch.

Switching the transmitter selector between COM1 and
COM2 changes both transmitter and receiver frequencies.
It is necessary only when a pilot wants to monitor one
frequency while transmitting on another. One example is
listening to automatic terminal information service (ATTS)
on one receiver while communicating with ATC on the
other. Monitoring a navigation receiver to check for proper
identification is another reason to use the switch panel.

Most audio switch panels also include a marker beacon
receiver. All marker beacons transmit on 75 MHz, so there
is no frequency selector.

Figure 9-4 illustrates an increasingly popular form of
NAV/COM radio; it contains a global positioning system
(GPS) receiver and a communications transceiver. Using its
navigational capability, this unit can determine when a flight
location in the communications radio.

Combination GPS-Com Unit.
Figure 9.4. Combination GPS-Com Unit.

crosses an airspace boundary or fix and can automatically
select the appropriate communications frequency for that

Radar and Transponders
ATC radars have a limited ability to display primary returns,
which is energy reflected from an aircraft's metallic structure.
Their ability to display secondary returns (transponder replies
to ground interrogation signals) makes possible the many
advantages of automation.

A transponder is a radar beacon transmitter/receiver installed
in the instrument panel. ATC beacon transmitters send out
interrogation signals continuously as the radar antenna
rotates. When an interrogation is received by a transponder, a
coded reply is sent to the ground station where it is displayed
on the controller's scope. A reply light on the transponder
panel flickers every time it receives and replies to a radar
interrogation. Transponder codes are assigned by ATC.

When a controller asks a pilot to "ident" and the ident button
is pushed, the return on the controller's scope is intensified for
precise identification of a flight. When requested, briefly push
the ident button to activate this feature. It is good practice
for pilots to verbally confirm that they have changed codes
or pushed the ident button.

Mode C (Altitude Reporting)
Primary radar returns indicate only range and bearing from
the radar antenna to the target; secondary radar returns can
display altitude, Mode C, on the control scope if the aircraft
is equipped with an encoding altimeter or blind encoder. In
either case, when the transponder's function switch is in the
ALT position the aircraft's pressure altitude is sent to the
controller. Adjusting the altimeter's Kollsman window has
no effect on the altitude read by the controller.

Transponders, when installed, must be ON at all times when
operating in controlled airspace; altitude reporting is required
by regulation in Class B and Class C airspace and inside a
30-mile circle surrounding the primary airport in Class B
airspace. Altitude reporting should also be ON at all times.