David Young
Technical Subject Areas
1. Subject – Navigational Equipment.
2. Introduction – What sets instrument flying apart from visual flying is the reliance on
navigational aids to assist the pilot in conducting the flight safely. A basic understanding
of each of the aids is vital in understanding how to use them and what their limits are.
3. Outline –
a. Discuss VORs.
i. Discuss how they work.
ii. Discuss how we determine our location using them.
b. Discuss DME.
i. Discuss how it works.
c. Discuss NDBs.
i. Discuss how they work.
ii. Discuss how we determine our location using them.
d. Discuss GPS.
i. Discuss how it works.
ii. Discuss how we determine our location using them.
4. Contents –
a. One type of radio aid is the VOR, or Very High Frequency Omni-directional
Radio Range.
i. A VOR broadcasts between 108.0 MHz and 117.95 MHz, which is in the
very high frequency range (hence the name).
ii. It has two signals: one omni-directional signal that points towards 360º
and another directional signal that rotates.
1. Every time the directional beacon passes through 360º, the omnidirectional signal is sent out.
2. When a receiver detects the omni-directional signal, a clock is
started.
3. This clock stops once the rotating directional signal is received.
4. By measuring the time between the receptions of the two signals, it
is possible to determine which radial you are “on.”
iii. Think of it as a radio station that shoots out 360º lines (one for every
degree of heading, although in reality it shoots out infinitely many lines).
1. These lines are called radials, and each radial is called by its threedigit representation of the heading the radial is in.
a. For example, the radial that shoots out directly east of the
VOR is the 090 radial because it shoots out 90º from the
VOR.
Young 2, Navigational Equipment
iv.
v.
vi.
vii.
viii.
ix.
2. By knowing which radial we are on, we can know our position in
relation to a VOR.
a. We use an instrument called an Omni-bearing Selector
(OBS) to help us figure out where we are in relation to the
VOR (refer to Figure A).
b. It should be noted that heading has NOTHING to do with
our indication on the OBS. Rather, our LOCATION in
reference to the VOR is important.
There are 3 different types of VORs: terminal, low and high altitude.
1. Terminal VOR – (1,000 ft – 12,000 ft) 25 nm radius.
2. Low Altitude VOR – (1,000 ft – 18,000 ft) 40 nm radius.
3. High Altitude VOR – (1,000 ft – 14,500 ft) 40 nm radius, (14,500 ft
– 18,000 ft) 100 nm, (18,000 ft – 45,000 ft) 130 nm, (45,000 ft –
60,000 ft) 100 nm.
Before using a VOR, it is important to identify it. This is accomplished by
listening to a navigation radio with the VOR’s frequency tuned in and
verifying that the Morse code heard is the code depicted on your chart.
To dial in a certain radial, we rotate the card on the OBS around until that
radial’s number is centered at the top.
The course deviation indicator (CDI) is the needle we see on the OBS.
You can think of this as the radial itself.
There is also a TO/FROM flag.
1. If you center up the CDI with a TO indication, the course that
centers up the CDI is the course you must fly to get TO the VOR.
2. If you center up the CDI with a FROM indication, the course that
centers up the CDI is the course you must fly to go AWAY from
the VOR.
3. Note that as if you have the CDI centered with a TO indication and
you fly directly over the top of the VOR, the flag will switch to a
FROM indication.
Once you have a course centered up, fly a heading that will keep you on
that course and the CDI centered.
1. If you are flying to the station and you have a TO indication, then
always fly TOWARDS the needle.
a. The same applies if you are flying from the station with a
FROM indication.
2. It is possible to fly towards the station and get a FROM indication,
and this happens when you put the course that is reciprocal to the
course needed to get to the station.
Young 3, Navigational Equipment
x.
xi.
xii.
xiii.
xiv.
a. This will create reversed sensing, which means that you
now must fly away from the needle.
3. IMPORTANT: it is good practice to avoid reverse sensing. So, if
you need to fly to the VOR, center up a course that will get you to
the VOR. If you need to fly away from the VOR, center up a
course that will get you away from the VOR.
Refer to Figure B for an example of what you must do to track a radial in
a crosswind.
So to actually navigate with VORs, center up the CDI with a course that
will get you to the station with a TO flag.
1. This will require you to know relatively where you are in relation
to the VOR i.e. am I north, east, south, or west of the VOR?
2. This will get you going directly to the VOR.
3. From there, select another VOR along your route and repeat this
procedure.
4. Keep in mind that, for flight planning purposes, you should not
plan to use a VOR from further that 40 NM away from it.
a. You might be able to pick up a signal from that far out, but
it isn’t guaranteed, so you should not rely on getting signal
any further out that 40 NM.
Airways are usually just radials of different VORs strung together to make
“highways” through the sky.
Something called distance measuring equipment (DME) may help you in
determining your distance from a VOR.
1. DME measures the amount of time that it takes for radio waves to
be sent from the aircraft to a DME station (many times coupled
with a VOR). This time is then converted into distance, which can
even be converted into groundspeed.
2. Note that the distance given is NOT the distance across the ground,
but rather the distance from you up in the air, to the DME station
on the ground, otherwise known as slant range.
3. For example, if you were about 6,000 ft directly above a DME
station, the DME would read 1 nm even though you are directly
overhead the station.
A VOR/DME is simply a VOR station coupled with DME.
1. A VORTAC (VOR/TACAN) is a VOR station as well as a TACAN
station. DME is provided.
VOR CHECKS
xv. Every 30 days, a VOR check must be accomplished for flight under IFR.
Young 4, Navigational Equipment
xvi. You must record the date, place, discrepancy, and signature.
1. VOR Test Facilities (VOT) – available at some airports (check
AF/D), 360º FROM or 180º TO should center up within ± 4º.
2. VOR Checkpoints – available at some airports (check AF/D),
points on the airport where a certain radial intersects that point. ±
4º.
3. Airborne VOR Check – uses VOR checkpoints, ± 6º.
4. Dual System Check – you may check the indications of two
independent VOR systems on your aircraft against one another
when set to the same VOR. ± 4º.
b. Another type of radio aid is the non-directional beacon (NDB).
i. NDBs broadcast between 190 KHz and 1750 KHz.
ii. Their locations are found using a loop and a sense antenna.
1. Loop Antenna – consists of two insulated coils of wire that are
perpendicular to each other. This bi-directional antenna couples
with the magnetic component of the NDB’s signal.
a. The maximum voltage is induced when the antenna is
perpendicular to the NDB. This is called a null.
b. Nulls can happen when the NDB is either directly in front
of or behind the aircraft, thus necessitating a sense antenna
to determine which one it is.
2. Sense Antenna – an omni-directional antenna that couples with the
electrical component of the NDB’s signal.
a. It can determine if the NDB is directly in front of or behind
the aircraft.
3. By combining the information provided by the two components, it
is possible to determine the location of the NDB.
iii. Unlike the VOR where signal reception relies on line-of-sight, an NDB’s
signal follows the curvature of the earth and is available for receivers
much further away.
iv. Think of this as a stupid VOR.
v. In this case, there are no radials that shoot out of the NDB. Instead, you
have an instrument called the automatic direction finder (ADF), which
always points towards the NDB station, no matter what.
vi. Unlike a VOR, this time, your heading does matter.
1. For example, if your nose is headed straight towards the station,
the needle would point to the very top of the instrument.
2. However, if you turned to the right by 20º, that needle would
swing 20º to your left because you must fly 20º to the left to get the
needle back off your nose.
Young 5, Navigational Equipment
vii. There are 4 types of NDBs: compass locator, MH radio beacon, H radio
beacon, and HH radio beacon.
1. Compass Locator – 25 watts, 15 nm.
2. MH Radio Beacon - < 50 watts, 25 nm.
3. H Radio Beacon – 50 – 1,999 watts, <= 50 nm.
4. HH Radio Beacon – >= 2,000 watts, 75 nm.
viii. NDB signals tend to be adversely affected by poor weather.
ix. Before using an NDB, it is important to identify it. This is accomplished
by listening to a navigation radio with the NDB’s frequency tuned in and
verifying that the Morse code heard is the code depicted on your chart.
1. Unlike VORs, the NDB’s coded signal should be continually
monitored as NDBs are less reliable than VORs.
x. Two important NDB terms are relative bearing and magnetic bearing.
1. Relative Bearing (RB) – the value to which the needle points on
the azimuth dial (the compass rose around the instrument).
a. For example, if the NDB is 40º to your right, your relative
bearing to the station is 40º.
b. For example, if the NDB is 40º to your left, your relative
bearing would be 360º - 40º = 320º.
2. Magnetic Bearing (MG) – “to” the station is the angle formed by a
line drawn from the airplane to the station and a line drawn from
the airplane to magnetic north.
a. MB is different than relative bearing because relative
bearing is only the number of degrees you must turn right
to head straight for the NDB.
b. Magnetic bearing is the actual course you must track to get
to the NDB.
3. Remember that RB + MH = MB.
a. It may be necessary to subtract 360º from this equation if
the MB is above 360º.
4. To get the MB FROM the station, add 180º to the MB TO the
station.
5. Refer to Figure C for a visual of RB and MB.
a. In this case, our relative bearing would be what the needle
points to, or about 225º.
b. The magnetic heading is 030º.
c. So to get to the station, we must track a course of 255º from
our present location.
6. While flying, we will almost always have some sort of crosswind.
Young 6, Navigational Equipment
a. As we correct for the crosswind by crabbing, our ADF
indication will change because we have moved our nose
with relation to the station.
b. If our WCA is 10º to the right of course, then our ADF
should point to 10º left (or a RB of 350º).
c. For example, if our MB to the station is 340º and we must
hold a heading of 330º to correct for the wind, our ADF
would indicate a RB of 10º.
d. If you are holding a WCA in, but the ADF begins to move
further and further from the top of the instrument, then our
crab angle is too much, and we should reduce it to stay on
course.
7. When flying outbound on an NDB, the needle on the ADF will
point towards the bottom of the instrument.
a. The fundamentals of flying away from an NDB are the
same as flying towards it, but this time the wind correction
procedure is different.
i. Wind correction should be made in the direction
opposite of that in which the needle is pointing.
xi. The last radio aid is the global position system (GPS).
1. This system uses satellites orbiting the earth to pinpoint the exact
location of the aircraft.
2. To do this, an aircraft needs at least four satellites.
a. The satellites send out ultra-high frequency radio waves
that are received by both GPS antennae and control
segments.
i. GPS antennae are those found on aircraft and cars.
ii. The control segment consists of control stations
across the globe that update each satellite’s
EXTREMELY accurate atomic clocks.
b. The satellites continually send out radio waves that contain
the exact time of emission from the satellite.
c. When the GPS antennae receive the radio wave, they
measure the difference between the current time and the
time the satellite’s radio wave was sent, and compute the
distance.
3. Each of the four satellites the GPS antenna is using gives the user a
better and better idea of exactly where they are laterally,
longitudinally, and vertically in relation to the earth.
4. This information is then usually displayed visually on a map.
Young 7, Navigational Equipment
a. This map can make the process of finding out exactly
where you are in relation to towns, airports, and other radio
aids a cinch.
5. A useful function that you can use for GPS navigation is the
“Direct to” function.
a. Basically, you can input any airport or navigational aid
(such as a VOR or NDB) and have the map draw out a
course for you to fly to get from where you are to that
point.
b. This is obviously useful in navigation because you can see
on a map how to get back on course without having to do a
lot of math and drawing yourself.
c. Ideally, a combination of all these radio aids should be used to help you maintain
the best situational awareness possible when navigating.
d. Using dead reckoning to get from point A to point B while reaffirming your
location with pilotage, VORs, and GPS is the best way to make sure that you get
from point A to point B safely.
5. Evaluation –
a. The student can discuss the basic principles of a VOR and how to use one.
b. The student can discuss the basic principles of DME and how to use it.
c. The student can discuss the basic principles of an NDB and how to use one.
d. The student can discuss the basic principles of GPS and how to use it.
6. References –
a. PHAK, Ch. 14
b. Jeppesen Instrument/Commercial
Young 8, Navigational Equipment
Figure A
Young 9, Navigational Equipment
Figure B
Young 10, Navigational Equipment
Figure C