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, because 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 approach?

Papamac explains:

  1. 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 course heading.

  2. 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.

  3. Always intercept the Localizer course at no more than a 30 degree angle.

  4. 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.

  5. Always put the landing gear down at glideslope intercept. Good habit transfer and will help hold the glideslope.

  6. 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.

  7. 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 crosswind.

  8. 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 glideslope transmitter. 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 marked on the plate as a little square with the label GS, located about 1000' in from the approach end of the runway.

I followed 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 approach.

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 X-Plane?

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 ILS.

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 course?

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:
  1. Not all real airports have a functioning back course. Fewer have had their back course certified for use (meaning that it's been tested and found to be adequately reliable). X-Plane's back course always works, with the one exception given.

  2. 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 configuration!

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