Trying to learn about aviation, and looking through all the displays in the cockpit, and also the Garmin G1000, I am not sure where I see the distance to the runway touchdown point, or the start of the runway. Sure, I see the ILS glidescope indicator, telling me I am too high/low, but where is the runway?

Ergo, my question is this: If flying in heavy fog, dark night, let's say visibility down to 2 meters! how does the pilot know where to land? Some indication of the distance would be great.

Thanks a lot, much appreciated.

  • $\begingroup$ While distance to runway would be nice to see, isn’t an equivalent measure (provided you’re on glideslope) the altitude which should be readily available? $\endgroup$ Commented Jun 20, 2019 at 5:56
  • $\begingroup$ The three parameters (height, horizontal distance to touchdown point, glideslope) are linked. Get 2 of them and you can deduce the other one. Once on glideslope, you will touch the runway at the desired touchdown point. $\endgroup$
    – Manu H
    Commented Jun 20, 2019 at 8:01
  • $\begingroup$ "Ergo, my question is this: If flying in heavy fog, dark night, let's say visibility down to 2 meters! how does the pilot know where to land?" They don't land. There is something called a "decision height" where if you cross that height without visual identification of the runway, you are required to go-around. There are no 0/0 (0 visibility) landing systems in use today (although they exist) and certainly none for light GA aircraft. The ones that do exist for commercial airliners are a type of autopilot so the pilot would not do anything but wait for the bump. $\endgroup$
    – Ron Beyer
    Commented Jun 20, 2019 at 14:13

2 Answers 2


There is no distance to the touchdown point because there isn't a set touchdown point. there's no runway start distance because that's not what you are aiming for. The purpose of the ILS is to get you close enough to the runway to complete a landing visually. If the visibility is so bad you cannot see the runway even when you are right on top of it then you need an airplane with a completely automated landing system to legally shoot the approach.

What you do have a DIS (Distance) reading in nautical miles to the ILS at the top of the screen, which usually tells you all you need to know. This distance is what you use in the approach procedure which you get from the approach plate for the runway and category of approach you are doing. If you get to the missed approach point, which is a set distance from the ILS, without seeing the runway lights then you must go around.

I'm going to assume you are working with a simulator like x-plane or MFS, in which case you aren't bound by procedure, and you can give it a try without endangering anyone. The ILS in most airports is placed right next to the runway, about where you'd want to aim a touchdown, so in a white out condition you would follow it down as far as you can until you contact the ground. It's been successfully done in emergencies, there's a good deal of pucker factor involved.

  • $\begingroup$ A touchpoint is defined in UAV landings and ILS landings. $\endgroup$ Commented Jan 22, 2020 at 16:33

With visibility of 2 meters you cannot land an airplane. Cat IIIb allows no decision height and auto land the plane to touch down point. Even in Cat IIIb, the highest class available, you still need 150 feet of runway visual range in order to perform a safe roll out. When Cat IIIc is available you may perform your 2 meters visibility landing.

Until then your only option is to divert to another airport.

Related : How can landing in zero visibility be safe?

  • $\begingroup$ Thank you vasin1987. But is there any reading/ indication, that tells how far you are from the airport/ runway? Or how does a pilot know when to lower altitudes on the approach (for discussion sake assuming it is a straight line to the runway for even 30 miles? $\endgroup$
    – Ben
    Commented Jun 20, 2019 at 7:11
  • $\begingroup$ @Ben en.wikipedia.org/wiki/Distance_measuring_equipment Tells you the distance from navaids which usually colocate in the airport. For height above runway you can try radar altimeter. $\endgroup$
    – vasin1987
    Commented Jun 20, 2019 at 7:33
  • $\begingroup$ @bogl i suggest that could be a good new question about mandatory equipment. I have no knowledge about this but I know of no Cat IIIc in operation. $\endgroup$
    – vasin1987
    Commented Jun 20, 2019 at 7:44
  • 1
    $\begingroup$ Found it on en.wikipedia.org/wiki/Instrument_landing_system: "CAT I relies only on altimeter indications for decision height, whereas CAT II and CAT III approaches use radar altimeter (RA) to determine decision height." $\endgroup$
    – bogl
    Commented Jun 20, 2019 at 8:22

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