Chapter Three Fundamentals of Instrument Navigation

CHAPTER THREE

FUNDAMENTALS OF INSTRUMENT NAVIGATION

300. INTRODUCTION

In order to obtain a thorough understanding of the procedures discussed later in this manual and

to navigate properly on instruments, you must be able to visualize your position in relation to a

Radio NAVAID. To accomplish this, you need a thorough knowledge of the navigational

instruments, how they function, and what they depict. The remainder of this section will provide

a brief radio instrument orientation.

The EHSI is the most valuable instrument in the aircraft for maintaining orientation. You are

already familiar with one function of the EHSI. By checking the number beside the heading

index, at the top of the instrument, you are able to determine the aircraft's magnetic heading.

The EHSI has an additional function. This function allows the aircrew to determine its position

relative to a selected VOR station. The combination of both functions in one unit makes the

EHSI the primary navigation instrument in the aircraft.

In addition to a compass card, the EHSI contains two bearing pointers referred to as needles.

These needles can be selected independently to display either GPS or VOR information. For

standardization purposes, the single-needle will always be used with the VOR, and the double-

needle with the GPS. For the purposes of this discussion, we will refer to the needle selected to

display VOR information. The head of the needle points to the selected station and the tail of the

needle indicates the position of the aircraft from the station in terms of radials. Assuming all

equipment is working properly, the needle indicates both relative and magnetic bearing to its

associated station.

NOTE

In this example, only the single bar VOR bearing pointer will be

considered.

The lines extending from the VOR station in Figure 3-1 represent radials. The equipment in the

aircraft receives the signals from the station and displays this information on the EHSI so you

can then determine the aircraft's position relative to the VOR station.

In this example, the aircraft is flying a heading of 360. The tail of the VOR needle is on the

210 mark of the EHSI indicating a position southwest of the VOR on the 210 radial. In

relative terms, the VOR station is 30 to the right of the aircraft's nose.

FUNDAMENTALS OF INSTRUMENT NAVIGATION

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