INSTRUMENT FLIGHT RULES WORKBOOK
The transponder has a five position function switch (Figure 1-19):
The OFF position disconnects the unit from the aircraft power supply. In the STANDBY
position, electrical power is applied, but the set is not emitting a signal. In the ON position, only
the Mode 3 (identification) portion of the transponder is operational. In the ALTITUDE
position, both Mode 3 and Mode C are operational. In the TEST position, the pilot can confirm
proper operation of the transponder if the REPLY light illuminates. The reply light also serves
as the IDENT button. The IDENT feature allows the controller to quickly distinguish a specific
aircraft from the other aircraft on his radar scope. When a pilot pushes the IDENT button, the
target the controller sees will become highlighted and begin to flash.
BEARINGS, RADIALS, AND COURSES
Prerequisite to the study of the RMI, and the CDI, the student aviator must thoroughly
understand three terms basic to determining horizontal direction from a fixed geographical point.
The three terms are bearing, radial, and course. A bearing is used to measure the horizontal
direction to or from a Non-directional Radio Beacon (NDB). For example: the 090 bearing
"FROM" a NDB facility originates at the facility and extends eastward (Figure 1-20). The 090
bearing "TO" a NDB facility originates west of the facility and extends eastward, terminating at
the facility. To eliminate the confusion of bearing "TO" and bearing "FROM," ATC controllers
will use the terms "COURSE TO" and "BEARING FROM" a facility.
Figure 1-20 Course "TO" and Bearing "FROM"
A radial is a magnetic bearing that extends from a VOR, VORTAC, or TACAN station. Each
VOR, VORTAC, or TACAN has 360 radials extending from it. An aircraft using a VOR for
instrument navigation is always on one of the 360 radials extending from that station.
1-26 INTRODUCTION TO AIRBORNE NAVIGATION AND COMMUNICATIONS
EQUIPMENT AND PRINCIPLES OF OPERATION
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