Navaids and Instrument Landings
How do I find the
location and frequencies of navaids?
X-Plane displays VORs (VHF Omni
Ranging) and NDBs
(Non-Directional Beacon) in the maps. Airport approach plates also
display the ILS markers.
The simplest way to find the navaids at
or near an airport is to
place yourself at the airport: From X-Plane's menu bar, select Location
-> Place Aircraft by Airport. Either scroll the list (tricky,
it's huge) or type in the name of the airport. (This may also be
problematical, because the names of the airports are not always
obvious.) Anyway, once you're at the airport, simply display the
approach plate - select Plates and click on the airport name. The
approach plate will display the frequencies for the ILS and nearby VORs
and NDBs. The Local Maps will display the VORs and NDBs for the area
around the airport.
If you have no idea of the airport name,
you can position
yourself in the general area by opening the Planet Map and clicking on
the location. This will put you at the nearest airport.
If you want to search a list, all the
navaids are stored in the
text file Resources\Earth Nav Data\nav.dat. Just open this in any text
editor that can handle a large file. Robin's data
file definition pages explain the format of the data. ILS markers
are identified by the ICAO code of the associated airport.
You can also open Resources\Earth Nav
Data\apt.dat and search
for airport names. This is a good way to find the ICAO code for an
airport when you only know the name. It's also a good way to find
airports when you're not sure of the exact name.
How do I fly an ILS
- When using an HSI, always set the front course heading, never
the back course. With a CDI, it makes no difference to what course you
set the selector but for good habit transfer, set it to the front
- Flying the opposite direction from the set course will result
in reverse sensing with a CDI. (See Back Course
description below.) HSI indications
will always be directional if properly set to the front course.
- Always intercept the Localizer course at no more than a 30
- Approach the Glideslope from below, never above. There are
false glideslopes at steeper angles than 3 degrees but none below that
angle, and most autopilots won't capture from above.
- Always put the landing gear down at glideslope intercept. Good
habit transfer and will help hold the glideslope.
- The rate of descent on the VVI to hold the published glideslope
angle (usually 3 degrees) is a function of ground speed (GS). A rule of
thumb is that it's the speed in nautical miles per minute (NMM) times
the glideslope angle (60 Knots = 1 NMM * 3 = 300 feet per minute, etc).
[The rule of thumb I like to use for a 3 degree glideslope, which is
most of them, is 5 fpm per knot. Same answer, less arithmetic.- Andy]
Set the power to give the desired airspeed and pitch to maintain the
proper angle as measured by the Attitude Indicator (roughly -3 degrees)
and verify the proper vertical speed on the VVI.
- Make very small corrections while tracking the localizer. A 1
to 2 degree heading change (some people advocate using only rudder
pressure to "skid" the heading change) will make tracking much easier
for you. Try to pin down the precise heading that will hold the
localizer course before passing the outer marker. 1/4th of the direct
crosswind component is sufficient at 120 Knots to compensate for
- The minimum descent altitude is called Decision Height. It's
the altitude at which you decide whether or not you can continue the
approach to touchdown. If the decision is made at that point to make a
missed approach (MAP) it's expected that the aircraft will descent
further as it's reconfigured for climb.
Why don't I get a
glideslope indication when I'm tuned to an ILS?
Not all ILS installations have a
If there isn't one you'll get the GS warning flag in your VOR head or
HSI. To check if an airport has a glideslope transmitter, position the
local map over the airport and zoom in so you can see the details.
If there's a glideslope transmitter for your runway, it should be
on the plate as a little square with the label GS, located about 1000'
in from the approach end of the runway.
the ILS at South Lake Tahoe and it didn't guide me to the runway
South Lake Tahoe Airport (KTVL) and some other airports have what's
called an offset localizer. Other well-known examples include
Innsbruck, Austria (LOWI) and the now closed Kai Tak Airport in Hong
Kong (VHXX). The localizer guides you to a point where you can see the
runway threshold and land, but the final stage of the landing must be
done visually. The approach path does not line up with the runway
centerline, so you must make a turn near the end of your approach. The
usual reason for an offset localizer is that there are obstacles (like
mountains) in the way of a straight-in approach. At Lake Tahoe, you fly
south over the lake near the eastern shore and turn right to land. The
mountains east of the lake are much too tall to permit a straight-in
Always study the map and approach plates for an airport before making
an instrument approach. X-Plane's local map will show you the
relationship of the navaids to the runways. But for proper instrument
approach procedures, there is no substitute for a proper approach
plate. See the charts links on the
Resources FAQ page
for sources of online approach plates.
Is there ATC available in
Yes, via an ATC menu (which does not
require the use of
radio frequencies). Ground, Tower, Departure, Approach and Centre ATC
are simulated, albeit somewhat simplistically.
You can request vectors to an airport,
request ILS, LOC or
visual approaches. You can obtain ATIS for an airport. You can request
takeoff and landing.
Filing a IFR and VFR flight plans with
ATC are supported, but
without waypoints. ATC will only check that you meet your filed
altitude. It does not check if you stray of course or even head off in
the opposite direction. When close to the destination airport, X-plane
ATC will start you on your descend and vector you're in for an
instrument approach (assuming ILS or LOC available at active runway).
You can also request a PAR approach for
runways that have an
Unfortunately much of X-Plane ATC is
canned. For example,
declaring a missed approach. X-Plane ATC responds with a simple message
telling you to declare your intentions when able. It simply
assumes that you have the plates and will fly the published missed
approach, hold and then request vectors for another approach.
What is a localizer back
Most localizer antennas transmit a
signal in both directions. The primary published signal (that usually
extends over the runway along the approach path) is called the front
course. The back course extends in the opposite direction and can in
many situations be used to fly an approach. This allows both directions
of a runway to be served by a single localizer trasmitter.
When you fly a back course approach, your CDI sensing will be reversed
because the two sides of the localizer signal are reversed from your
point of view. This particularly affects the use of a VOR head to fly a
back course. If the CDI needle points left, you must fly right, not left, to get on course.
If you're using an HSI, you set the HSI's OBS to the front course, ie.,
opposite to the direction you're flying. This
mechanically reverses the deflection of the CDI; the double reversal
gives you a true course indication and you can simply "fly the needle"
as you would for a front course.
Another consideration to remember with a back course approach is that,
with the exception of some rare cases, there is no glideslope signal.
The back course signal can also be used to guide a missed approach
course. You simply continue to fly the runway heading, using the back
course signal from the localizer to guide you. In this case the CDI
sensing is "normal"; that is, a left CDI deflection means you need to
fly to the left to get on course.
Does X-Plane model the
localizer back course?
With some limitations, yes. X-Plane models a back course
for all localizers, except where the runway has localizers on both ends
operating on the same frequency. (More detail in a moment.) Compared to
real life, there are two limitations in X-Plane's modelling:
- Not all real airports have a functioning back course. Fewer
have had their back course certified for use (meaning that it's been
and found to be adequately reliable). X-Plane's back course always
works, with the one exception given.
- X-Plane's maps don't give any indication of a back course
signal. You just need to know that where a localizer exists you can fly
the opposite approach using the back course procedure.
The one situation where X-Plane does not
have a back course
localizer signal is where a runway has localizers at each end, but
operating on the same frequency. This is actually a pretty common
situation. In real life, the airport's controllers would be using one
runway direction or the other and switch on the appropriate localizer.
In X-Plane, there is nothing to make the decision of which runway
direction should be used, so X-Plane just automatically "switches on"
the localizer corresponding to the direction
you are approaching from.
You can get tripped up by this behavior
if you are not aware of
the airport configuration, because you will get a localizer signal
either way - either the front course of the "active" localizer, or the
back course if there is only one. However, the CDI deflection will be
opposite for the two cases. If you're using an HSI, you must set the
HSI to the forward approach direction in the dual localizer case, and
to the reverse direction in the single localizer, back course case.
Always check the map and make sure you understand the airport
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