500 ft altitude with GPS only (without vertical guidance). LPV minimum is 300 ft.
Category III ILS minimum is 200 ft, Cat II -- 100 ft. But there are a lot of airports where ILS is not available.
Counting airports doesn't give you an accurate picture, because just about any airport can have a GPS approach, since the whole point is that it doesn't require any ground equipment. That doesn't mean those approaches get much use, because people don't fly into those airports all that much, especially not on instrument approaches.
I fly out of an airport with a published GPS approach and no ILS, and people use the GPS approach on well under 1% of the total landings there. Any reasonably busy airport will have ILS.
I fly airplane without IFR GPS (IFR student), but ATC is trying to assign us GPS approach all the time (when coming into airport with ILS). As far as I understand, GPS approaches are used, even if they are less critical in busier airports. Besides, sometimes ILS is not available in bigger airports as well.
>Due to the complexity of ILS localizer and glide slope systems, there are some limitations. Localizer systems are sensitive to obstructions in the signal broadcast area like large buildings or hangars. Glide slope systems are also limited by the terrain in front of the glide slope antennas. If terrain is sloping or uneven, reflections can create an uneven glidepath causing unwanted needle deflections. Additionally, since the ILS signals are pointed in one direction by the positioning of the arrays, glide slope supports only straight-line approaches with a constant angle of descent. Installation of an ILS can be costly because of siting criteria and the complexity of the antenna system.
>ILS critical areas and ILS sensitive areas are established to avoid hazardous reflections that would affect the radiated signal. The location of these critical areas can prevent aircraft from using certain taxiways[3] leading to delays in takeoffs, increased hold times, and increased separation between aircraft.
You don't think that the ILS system could be vulnerable to an attack similar to this? The main point of the article is that we rely on tech that is insecure to give us our location and that can be influenced by an outside source. If that outside source is nefarious in nature then we can experience some real issues.
Yes, you can indeed hijack an ILS system. At least during WW2.
For more information regarding what happens if someone alters the altitude of a plane, see [2].
For example ultralights are pretty much "You're small and light enough not to cause much damage when you crash; don't do anything stupid". So yes, I am quite sure there are heavier-than-air flying machines carrying humans and a GPS unit as their sole navigational tool. As if you need advanced tools for what a ultralight can actually handle in practice, LOL.
On the other hand if you go to the E-CFR and look at FAA reg 91.205 if you want to climb above/thru FL240 you need a working DME or RNAV kinda implies any commercial operation must have VOR-type gear installed.
Note that the same playback hack that works really well on GPS works even better and easier on old fashioned VOR gear.
Merely being required to have operational gear doesn't mean a little angel is perched on each pilot's shoulder making sure they actually do have the gear, and they know how to use it, and they are actually using it.
(Scroll up to 1-1-19. Global Positioning System (GPS). The FAA's links are all wacky.)
This is the FAA's Aeronautical Information Manual.
http://aeronav.faa.gov/content/aeronav/acfstatus/Presentatio...
Yes, I'm sure that pilots routinely ignore the altimeter, air speed indicator, climb rate indicator, compass ....
GPS is useful, but no competent pilot ignores all of the other sensors and uses GPS alone.
The story here is that we thought we had designed a system which can do this without human interaction, and now/whenever it was discovered we're realizing we're not done yet. That this can be done by a person with a compass and a map is not a comment worth the text it's written with.
People who don't know much about GPS think the satellites are eternally autonomous but that is not the case. There are precisely two uplink control points on the planet which control them. Both in the USA as I recall.
Another interesting problem is lifetime mismatch. It would be foolish to create a system which depends on and could outlive the current GPS constellation.
Also being in the USA we tend to assume the fedgov is on our side and our side is everyone's side, but the rest of the world has found out the hard way many times over to never assume that is or will always be the case. So absolute best case is you should never deploy a worldwide system with a SPOF controlled by a foreign power.
"The story here is that we thought we had designed a system which can do this without human interaction"
No it was designed for humans (mostly US soldiers) to geolocate themselves, so they could help orient themselves on paper maps. This whole idea of pasting a navigation system, or even worse, an autonomous navigation system, on top is a good example of feature creep resulting in systemic failure.
You probably could design a redundant, tough, reliable, world wide (or at least, wide range) autonomous navigation system. It would not look anything like GPS. It would probably look a heck of a lot like a weird cross between the VOR system and authenticated LORAN. It would take a lot longer than a HN post to nail it down exactly, but I'm sure that whatever it optimized down to, it wouldn't resemble GPS very closely. In the grand tradition of all copier machines being called Xerox machines, I'm sure that whatever this successor system is called, the general unwashed masses will continue to call it a "GPS" to the immense confusion of people who actually know what they're talking about.
A planetary scale authenticated mostly decentralized web of trust mesh network of millions of stationary beacons and mobile inertial navigation systems with computational countermeasures to fight intentional bad actors? Probably providing global internet access via the mesh while you're at it, because it's there?
And GPS isn't what I was talking about, the automatic navigation system on the $80 million yacht was the system we designed which we thought could be run without human interaction.
And your paranoid delusion that the US can/would use its GPS satellites offensively is just that - paranoid delusion.