Bearings, Radials, and Courses

CHAPTER ONE

INSTRUMENT FLIGHT RULES WORKBOOK

The transponder has a five position function switch (Figure 1-19):

OFF

SBY STANDBY

ALT ALTITUDE

TST TEST

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.

111.

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