Lesson 13 Radio Navigation


What does VOR stand for?

VHF Omni-directional range

108.0 to 117.95 MHz

Operational for line of sight only

Accuracy to within +/- 1˚

Morse Code is the only way to ID for sure

Test -….- code is for alerting pilots when maintenance is being done.

The VOR Sure its cool, but how does it work?

It radiates 2 signals

1st one is in all directions (Omni-directional)

2nd one is rotated about a point (Directional)

Airplane receives both signals, looks at the difference between the 2, the result is the radial

360˚ the two signals are in phase

180˚ the two signals are out of phase by ½

270˚ the two signals are out of phase by ¾


Course Roughness

Irregularities caused by terrain

West Practice Area

RPM settings may cause fluctuations

The Cone of Confusion


VOR Ground Checkpoint

Accuracy of the tests

The VOR High Service Volume

The VOR Low Service Volume

The VOR Terminal Service Volume

The VOR Head


OBS Omni-bearing Selector

CDI Course Deviation Indicator

The scale is 10˚ either side, each dot is 2˚

Ambiguity Indicator TO/FROM and OFF or NAV


The white flag is the active indication for the ambiguity indicator


Freq Range 962 to 1,213 MHz

Usually co-located with VOR

Usually freq is paired with VOR so that when you select VOR freq you get DME freq automatically.

DME may exist on its own or with another nav aid such as ADF but will have a VOR freq. published for access.

Required by FARs above 24,000 feet


DME comes in three flavors:





DME is an active system

There is a transmitter and receiver on both ends

Airborne unit sends signal to ground unit

Ground unit replies

Airborne unit measures the time it takes

12 microseconds = 1 mile for a radio wave

A pair of pulses is sent out specific to that airborne unit

Max range is 200 NM

Slant range distance compensate 1 mile for every 1000 feet

The Transponder

May be thought of as a microwave transmitter/receiver.

The radar antenna is also a transmitter/receiver

It will overpower the transponder so it cycles on and off 800 times a second with a target 40 miles out

Primary radar – just picks up reflected energy

Secondary radar – picks up transponders reply


The ADF is in the airplane

The NDB is on the ground

Basically an AM radio station designed for navigation use.

If fact you can use AM radio stations for navigation.

NDBs usually operate in the L/MF (low to medium frequency) of 190 to 535 kHz


How about that switch with all the funny abbreviations?

ADF puts the unit in nav mode, uses the loop (gray box) antenna on the bottom of the aircraft

ANT puts the unit in receive mode and switches to the big long antenna that goes from the top of the cabin to the tail.

BFO puts the unit in Beat Frequency Oscillator


ADF interpretation

MH + RB = MB to

MH is given info for fixed card

For moveable cards read the heading at the top

RB is the bearing measured clockwise from the nose of the aircraft

MB is the bearing measured clockwise from North

Moveable card ADF/NDB

The needle points to the magnetic bearing to

To get Relative Bearing use your formula

Figure 1

MH + RB = MB to

330 + RB = 210

RB = 120 (210-330)

Take 360-120 =240 RB to

Moveable card ADF/NDB

To get Relative Bearing use your formula

Figure 2

MH + RB = MB to

315 + RB = 190

RB = 125 (190-315)

Take 360-125 =235 RB to

Fixed Card ADF/NDB

On these, the needle points to the RB to

For MB use your formula

Figure 4 MH of 320

MH + RB = MB to

320 + 225 = 545-360=185

To get the bearing from don’t forget to add 180


There are 24 satellites in the constellation

They sit at 10,900 miles and orbit in about 12 hours

There are usually 5 that can be “seen” from anywhere on earth

The signals travel at the speed of light 186,000 miles per second

This requires clocks with accuracy in the billionths of a second (1 foot equals 1 billionth of a second)

The receiver calculates a time distance problem to figure range from a minimum of 4 satellites to determine position.



Stands for Area Navigation

Basically a VOR/DME computer

You tell it a radial and a distance and it fixes a waypoint at that location

Limitations are you have to be in range of a VOR/DME at all times

GPS is replacing this equipment


Stands for Instrument Landing System

Consists of a Localizer, which provides course guidance and a Glideslope which provides vertical guidance.

Very accurate, to within 25 feet at the threshold


Stands for Long Range Navigation

On its way out, but is dying a hard death

Works on the same principle as GPS only the stations are ground based

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