The VOR & it's Instruments

What does      V - O - R     stand for?

Omnidirectional

VHF = Very High Frequency

Radio Range

VOR uses = 108.1-117.95 Mhz

(108.1-111.95 MHz = all odds tenths are LOC Frq.)

Frq Band = 30 – 300 Mhz

A radio antenna that sends waves in all directions (0-360 deg) – 'omni' = all (latin)

Even though modern navigation systems such as the GPS is becoming the new Standard, the VOR is still one of the biggest

Ground-Based navigational aids available. The stations still connect many airways and it can be great for situational awareness.

Besides, there are still many approaches in the world that use the VOR as the main means for navigation.

And, it's still a good back up for navigation, in case the GPS should fail or become unreliable.

Doppler VOR – Ground Station (with DME)
doppler vor.jpg

Depending on their configuration the ground station can look differently.

VORTAC

Formerly made and used by the forces, VORTAC is also usable for the general aviation and includes DME.

A VORTAC is a station that combines a civil VOR with a TACAN in one piece. Thus, the station includes azimuth (horizontal guidance) for civil and military navigation as well as DME. DME operates in the UHF band of 960-1215Mhz. It provides distance information up to 390 nm.

VORTAC.jpg
 

What cockpit Instrument(s) is/are used with the VOR?

CDI

What does

stand for?

Course/Center

Deviation

Indicator

Course index (yellow triangle)

CDI needle​

2° Variation from radial/course per dot

CDI.jpg

Unreliable signal flag (or red/white color)

TO/FROM Flag  

OBS knob​

a CDI needle which is either moving horizontally OR swinging away from a course (left/right), indicates your
deviation (how many degrees you are away) from your selected course/radial.

- The compass card can be moved with the so-called OBS (Omni-bearing Selector) knob.

- The instrument also includes a TO/FROM Flag (triangle =        /      ) as seen in the pictures above/below, indicating

your position in relation to/around a VOR-Station. It does not show whether you fly to the station or away from it.

 

- If you want to fly or track a course directly TO a VOR the triangle should be pointing UP (      ) → Why?
You do not want reverse sensing, thus you should choose a course/bearing that is 90 degrees in either direction of your current heading.

- If you or ATC would like to know where you are in relation/around a VOR Station, you need a FROM flag,

a triangle pointing DOWN (      ). This position is expressed in 'Radials', not courses.

for VOR only

VORonly.jpg

Needle* moves horizontally 
left/ rigth, 
aka – 'azimuth' 

*'CDI'

for VOR only

VORonly_2.jpg

Needle* moves horizontally 
left/ rigth,
aka – 'azimuth'

for VOR/ILS

VORiLS_2.png

Vertical needle* moves left/right;
Horizontal needle moves up/down

for VOR/ILS

VORiLS.jpg

Vertical needle* moves left/right;
Horizontal needle moves up/down

 

The CDI 'functions' also exists in another instrument called...

What does

HS – I

stand for?

Horizontal

Deviation

Indicator

NAV WARNING FLAG

reminds you about inadequate NAV signal

Heading Warning Flag

IF 'ON', reminds you of a power loss to the gyro. Course indications remain usuable/heading indictions DO NOT!

shows selected heading

shows deviation from course/radial

HSI.gif

Arrowhead shows selected course

To/From Triangle

Heading (Hdg) Selector

GlideSlope Indicator - ea. dot ~ .04° (deg)

Course Selector

ea. dot = 2° off (deviation) from your course/radial

Now, what is the difference between a regular CDI and the HSI?

Well, both basically indicate where your A/C is situated in relation to your selected

course or radial, BUT!....

 

the HSI is an “ALL-IN-ONE” Instrument, combining a Hdg & Center Deviation Indicator, and it's compass card is connected to a so called “flux gate”, which is an electro magnetic compass that is not fooled, irritated or affected by magnetic dip = (which increases towards the earth poles). Thus, it consistently shows you the right heading, and does not need to be reset like a regular Hdg Indicator.

 

The other advantage of the HSI, is, that it does NOT have “REVERSE SENSING”.

 

VOR Range & Service Volumes

P0005.jpg

What is the Zone of Confusion?

The Zone or Cone of Confusion, as the second terms already implies, represents a cone-shaped area

(as illustrated in the picture above)

that extends far over a VOR station, but only within a +/- ½ radius around it.

Within that area, (covering only about a half a mile radius around a station), the pilot will experience a loss of signal coverage. During that relatively short moment, usually lasting for a couple of seconds only, depending on the a/c speed, the pilot will see a red NAV flag on his VOR Instrument, showing him the signal loss.

 

If the VOR has DME, it'll show you your altitude in (terms of) NM during this time.

Ex: a/c flying @ 2000 ft = 0.5 nm

-OR-

If you are flying towards/away from the station at 10.000 ft, distance information of more than

11nm are usually accurate.

 

How DME works?

DME, short for 'Distance Measuring Equipment' provides the Pilot with distance information

To/From a VOR Station IF the station has DME.

 

The airplane sends out a signal, also known as an 'interrogation' directly to the Station from which it will be sent back to the airplane immediately. The interrogation can also be understood as a signal request to the VOR Station. The airplane's receiver will calculate the time it takes for the signal to travel back and forth and will then convert it into distance information (nm).

Since the airplane is flying at an altitude, the signals sent by the airplane travel a 'diagonal' way, which is also called 'Slant Range'.

Therefore, as you get closer to the station, the indicated distance will usually be a little bit further than the actual (horizontal) distance. Otherwise, DME should be accurate within +/- 0.2 nm

The biggest error in indicated distance will be at higher altitudes directly over the station. At high

altitudes, your DME shows your height in nm.

Example:

If you cross a station at 6000 ft, the distance indicated will be around 1 nm.

 

Here is an illustration

slantRange.jpg

Your DME instrument usually also provides you with groundspeed information.

However, if this should not be the case, you can use the following Mental Math formula:

 

GS = 60* X dist. travelled in 1 min.

* formula is based on 1 hr. of flight.

 

VOR

Line – Of – Sight

Limitation

 

What is Line – Of – Sight?

NOT IN THE LINE - OF – SIGHT

The pilot isn't theoretically able to see the station → 'No Signal Reception'

LineOfSight.png
plane.png
LineOfSight.png

 IN THE LINE - OF – SIGHT

The pilot isn't theoretically able to see the station → 'Signal Reception'

plane.png

VOR Instrument Accuracy Checks

What is a VOR IAC and when are they required?

 

As the name implies, a VOR Instrument accuracy check makes sure that the CDI has a certain accuracy, so you can use rely on it's indication while using it for navigation.

 

There are 4 different ways to check that accuracy:

 

THE 'VOT'

1. choose the frq – you can find it for in the AFD or FAR/AIM for your airport, IF it has one.

2. ID the station – you should hear a TEST code signal

3. Tune the OBS to 180 – the CDI should center with a TO indication; or with at 000 with a FROM indication
(max allowed error is +/- 4 degrees)

THE 'VOR GROUND CHECKPOINT'

1. Taxi to a designated checkpoint on the ground and align your airplane with the arrow you see on the ground

2. ID the station

3. Turn the OBS to the designated radial for this checkpoint

(max allowed error is +/- 4 degrees)


THE 'VOR AIRBORNE CHECKPOINT'

Use either a checkpoint along a rdial over a designated landmark by the FAA

IF NOT available, choose your own landmark over a radial that corresponds with a Victor airway.

(max allowed error +/- 6 degrees)

THE 'DUAL VOR CHECK'

For the this check your a/c must be equipped with 2 independent VOR indicators (CDI's) using the same antenna.

How to perform the check:

1. Tune NAV-1 and NAV-2 to the same VOR frequency and ID them.

2. Choose the same radial on both Instruments (above the index with the OBS)

3. Observe and compare the needle (CDI) accuracy of both instruments against each other.

The deflection difference from the center (dotted vertical line) of both CDI's should NOT be bigger than 4 degrees between each instr.

Example:

CDI of Nav-1 indicates 2 deg deflection to L/R

CDI of Nav-2 indicates 3 deg deflection to L/R

difference = 1 degree (= within +/-4 degrees)

CDI of Nav-1 is centered

CDI of Nav-2 is 5 deg off from center

difference = 5 deg (= not within +/- 4degrees)

When is a VOR-Check required?

 

Accuracy checks are required every 30 days.

Results must be documented in the aircraft's logbook or other kind of record and also

require a signature by tester.

 

The following information must be recorded:

 

                                                                                                 D - DATE

                                                                                                 A -  ACCURACY (ERROR)

                                                                                                 P -  PLACE (POSITION)

                                                                                                 S -  SIGN

 

 

VOR NAVIGATION FORMULAS

(you should be flying perpendicular (in a right angle) to the station or radials)

 

How to figure out the Time to a station:

 

seconds of bearing change

degrees of bearing change

 

How to figure out the Distance to a station:

 

        min of bearing change X tas (kts)

degrees of bearing change

 

 

 

Don't understand this formula?

In both formulas, you take the seconds/minutes it takes to pass bearings (radials) and

divide them by the number of bearings (radials) you have actually passed at the end.

For 'dist to station' info, you must multiply the minutes by the TAS before dividing it by the

number of bearings (radials) you have passed.

Min to Station

Dist. to Station