How do you not mess up ILS on parallel runways? There are many airports with ILS and parallel runways, how do you select which ILS for the runway you want?

For example there are RWY 22L AND 22R and both of them have ILS enabled. How does the pilot know on which ILS he is flying?


2 Answers 2


The two ILS approaches on parallel runways will have a different ILS Localizer frequency. The pilots will select the correct approach from the charts and then either manually tune in the correct frequency or (for more modern aircraft) select the approach in the flight management computer, which will then automatically tune the correct frequencies. Before actually flying the approach, the pilots will cross-check the morse code identifier either by listening to it or (for more modern aircraft) by reading it off the displays.

Below you can see the ILS charts for the Runway 27L and 27R approaches at London Heathrow (source). I marked the frequencies and the identifiers (as they will be displayed on the screen, the morse code is depicted below).


  • $\begingroup$ where will they manually enter the ils frequency In the airplane? $\endgroup$
    – Mamad
    Jun 19, 2019 at 19:28
  • $\begingroup$ This depends on the aircraft. On a Boeing 737 for example, there are NAV tuning panels below the COM (voice communication panels). $\endgroup$
    – Bianfable
    Jun 19, 2019 at 19:33

ILS works with radio waves, just like voice communications, or other navigation aids like VOR. This means a specific approach will use a specific frequency for its navigation signal.

When the pilot is told what approach to expect, they will consult the chart for that procedure for the information needed to fly it. The top left corner of an ILS approach chart from the FAA will show the frequency for this approach:

ILS Freq

The pilot will tune the navigation radio to this frequency (or the FMC will do it automatically). Where they do this will depend on the aircraft. On the 737, the radios are tuned on the center console, just behind the throttle quadrant. The navigation radio tuner is just below the communication radio tuner.

737 Radio Tuning

Modified from source

Parallel approaches (or nearby ones) will be set up so that they do not interfere with each other and an ILS must be checked periodically to make sure that any deviations are within allowances.


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