Why do airports use ILS instead of GPS?

From what I’ve read ILS approach systems are expensive and costly to maintain, and GPS approaches require no equipment on ground, the only difference being ILS makes sure that there is no terrain in your way, so why don’t airports just use GPS and show that terrain is clear on the plates?

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Because, even today, more airplanes have ILS equipment than a GPS receiver for the approach. Also, it’s because ILS garuntees no terrain, allowing for CAT III approaches

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Some larger airports still use GPS especially on runways surrounded by ‘naughty’ terrain. As @Rodney_Buckland said, many airports use ILS as it usually has no conflicting terrain in the vicinity of the runway and for CAT III approaches(good for low visibility in case of dense fog)

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And each airline have their own rules, Swiss pilots are authorized to land with a GPS approach (VFR) but gulf-sisters airlines are obliged to make an ILS approach each time

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Well the short answer is ILS is already installed just about everywhere and has been paid for. GPS, which is actually referred to as RNAV/LNAV and a few other combinations is new, expensive and takes people like myself to build the approaches/routes/waypoints etc.

Also, the equipment required in the aircraft that would allow it to fly a “precision” RNAV approach is costly. Currently, what you will find at the majority or airports that offer an RNAV approach, is that it is not a precision approach as it it does not provide a glidepath, which in return requires an Minimum Descent Altitude, higher vis/ceilings.

An ILS on the other hand, is a two part system, providing location relative to the Runway Threshold (RWT) and a glidepath. Known as the Localizer and Glide Slope. Depending on which category the system is, determines the minimums of the approach.

If you have any questions about approaches and how they are built, ask away.

And a side note, Australia is the only country to have removed ALL their ground based navigation and gone entirely space based (GPS)

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i believe it’s because of terrain

These answers aren’t entirely true.

Because an airport offers an ILS approach, does not mean there isnt terrain. What it does mean though, is that the terrain does not penetrate a certain slope. There are other ways around dealing with terrain and or obstacles/obstructions. Increasing the Descent Angles, Increasing minimums and so forth. There is one area, known as the Visual Area, which is a small section, about .5 mi from the approach end of the runway that can not be penetrated.

So for example, lets take a very flat region, like the midwest in the United States, no terrain to worry about right? Well, start building a tall building within certain distance of the airport/runway to be used, and there goes your ILS. Its much more complicated than that but you get the idea.

ILS does not mean no terrain…

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Neither of us said that. What we did say is that it garuntees if your on the glideslope that you will not have any terrain conflicts

Each published approach gives you that…

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@THE-OP… you da man OP’s! Always an extremely reliable no BS source of accurate professional knowledge gained. Regards, Max

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and from what i know it ILS gives vertical and horizontal vs gps just gives one of them. A ILS to me is a much safer approach in bad conditions

It would be nice to have a list of people who are verified to answer questions accurately and without guessing. People are misled by inaccurate information.

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That’s a good idea. But yet again puts me out too cause I don’t know that much.

The intention is not to exclude people but let others know that the information that they are receiving, is from someone who has the general knowledge or better in the area of question. If you started to add accurate information you could be verified. (Not saying that you don’t supply bad information) 😉 You’re a pilot and have the general idea of how things work. I might make a thread in #meta to put this as a suggestion.

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I’d go for it. I’m just a basic VFR pilot so the general stuff I’m pretty good at. All the other fancy stuff with instruments and some procedures, I’ll let the more experienced guys take that

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Frankfurt is actually installing a GPS-based landing system which is meant to reduce noise level and should replace the ILS in the future.

Where has this information been found? Are you including ILS approaches in this, as I can guarantee you it’s incorrect if so? I’m assuming you mean the removal of VORs etc?

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From my experience of flying in the Geneva countryside, it’s safe to say that most of our ILS approaches at regional airports are being replaced by less costly (from what the FFA says about it) RNAV approaches.

The lowest minimum I have seen on a RNAV approach was roughly 300ft which is the minimum of the GNSS at LFRK.

(Here is what happens in the cockpit during a RNAV approach. Autopilot was disconnected at 200ft: https://youtu.be/uGMMFUX1pMk)

Nah GPS does give both

I think also one of the reasons why gps approaches are not profound is because the US military have control over them. They can choose to disable gps for civilian use anytime they wish.