The VOR & it's Instruments
What does V - O - R stand for?
Omnidirectional
VHF = Very High Frequency
Radio Range
Frq Band = 30 – 300 Mhz
A radio antenna that sends waves in all directions (0-360 deg) – 'omni' = all (latin)
VOR uses = 108.1-117.95 Mhz
(108.1-111.95 MHz = all odds tenths are LOC Frq.)
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)
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.
What cockpit Instrument(s) is/are used with the VOR?
C – D – I
What does
stand for?
Course/Center
Deviation
Indicator
Course index (yellow triangle)
CDI needle
2° Variation from radial/course per dot
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
Needle* moves horizontally
left/ rigth,
aka – 'azimuth'
*'CDI'
for VOR only
Needle* moves horizontally
left/ rigth,
aka – 'azimuth'
for VOR/ILS
Vertical needle* moves left/right;
Horizontal needle moves up/down
for VOR/ILS
Vertical needle* moves left/right;
Horizontal needle moves up/down
The CDI 'functions' also exists in another instrument called...
What does
H – S – 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
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
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
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'
IN THE LINE - OF – SIGHT
The pilot isn't theoretically able to see the station → 'Signal Reception'
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