5 ms·

There is more to it than that though. Aircraft often fly instrument approaches using GPS alone, getting to within 500 feet of the ground while still in clouds.

There is more to it than that though. Aircraft often fly instrument approaches using GPS alone, getting to within 500 feet of the ground while still in clouds. If someone could make the aircraft think it was just a couple extra miles in the wrong direction it could be disastrous.

blhack 13y ago
No they don't, they land with something called ILS https://en.wikipedia.org/wiki/Instrument_landing_system https://en.wikipedia.org/wiki/Instrument_landing_system
- hedgie13 13y ago
  There is more airports in US that have GPS only approaches than airports that have ILS approaches. For example: http://155.178.201.160/d-tpp/1308/05879R25.PDF http://155.178.201.160/d-tpp/1308/05879R25.PDF 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.
  - mikeash 13y ago
    A lot of small airports with very little traffic. 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.
    - hedgie13 13y ago
      True, they are less busy, but it does not mean GPS is not used for instrument approaches (as parent implied). 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.
      - toomuchtodo 13y ago
        ILS was not available on the SFO runway the Asiana aircraft crashed on ~2 weeks back: http://en.wikipedia.org/wiki/Asiana_Airlines_Flight_214 http://en.wikipedia.org/wiki/Asiana_Airlines_Flight_214
        hedgie13 13y ago
        Yes, but the weather was clear. No need for ILS in such weather.
        toomuchtodo 13y ago
        Unless of course you've never landed at SFO before in an aircraft you're barely type-rated on.
        mikeash 13y ago
        Neither should matter. A visual landing at any airport is pretty much the same, and the basics don't change for different aircraft. There's nothing at all tricky about a visual approach into SFO.
  - jnsaff2 13y ago
    You've got it backwards: CAT I is 200ft Decision Height (btw, not Minimum Descent) Cat II is 100ft Cat III is 0ft (with differing horizontal visibilities for IIIa/IIIb/IIIc
    - hedgie13 13y ago
      I am wearing paper bag for the rest of the day. Not enough caffeine in the morning.
- bargl 13y ago
  >Limitations Glide slope station for runway 09R at Hannover Airport in Germany >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.
  - iliis 13y ago
    As always when this comes up: https://en.wikipedia.org/wiki/Battle_of_the_Beams https://en.wikipedia.org/wiki/Battle_of_the_Beams Yes, you can indeed hijack an ILS system. At least during WW2.
    - snom380 13y ago
      You can hijack it, but there are monitoring systems in place to detect if something is out of place. Also, ATC will usually notice flight path deviations quite quickly, at least on manned airports with radar coverage.
  - yread 13y ago
    While ILS is generally considered to be the second most reliable instrument (after the windsock) it has its own problems... For example false glidescope, see http://www.ukfsc.co.uk/files/Safety%20Briefings%20_%20Presentations/Flight%20Ops%20-%20False%20ILS%20localiser%20capture%20BAE%20systems(1).pdf http://www.ukfsc.co.uk/files/Safety%20Briefings%20_%20Presen...
- ceejayoz 13y ago
  http://www.fastcompany.com/1266063/inside-next-gen-gps-based-airplane-landing-system http://www.fastcompany.com/1266063/inside-next-gen-gps-based...
mbrameld 13y ago
Do you have a source for aircraft flying using GPS alone? My understanding is that they rely on VOR and ILS systems.
- mcguire 13y ago
  http://www.faa.gov/air_traffic/publications/ATpubs/AIM/aim0101.html#aim0101.html.25 http://www.faa.gov/air_traffic/publications/ATpubs/AIM/aim01... (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.
- VLM 13y ago
  You can interpret that question a lot of different ways. 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.
- fnordfnordfnord 13y ago
  VOR system is on its way out. http://aeronav.faa.gov/content/aeronav/acfstatus/Presentations/11-02_Discontinuatoin_of_VOR_srvc-kward.pdf http://aeronav.faa.gov/content/aeronav/acfstatus/Presentatio...
eCa 13y ago
Considering how unreliable GPS altitude information is [1], I would like to not be on board when they do that.. For more information regarding what happens if someone alters the altitude of a plane, see [2]. [1] http://www.gpsinformation.net/main/altitude.htm http://www.gpsinformation.net/main/altitude.htm [2] http://www.imdb.com/title/tt0099423/ http://www.imdb.com/title/tt0099423/
asynchronous13 13y ago
> using GPS alone 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.

blhack 13y ago

No they don't, they land with something called ILS https://en.wikipedia.org/wiki/Instrument_landing_system https://en.wikipedia.org/wiki/Instrument_landing_system

hedgie13 13y ago
There is more airports in US that have GPS only approaches than airports that have ILS approaches. For example: http://155.178.201.160/d-tpp/1308/05879R25.PDF http://155.178.201.160/d-tpp/1308/05879R25.PDF 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.
- mikeash 13y ago
  A lot of small airports with very little traffic. 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.
  - hedgie13 13y ago
    True, they are less busy, but it does not mean GPS is not used for instrument approaches (as parent implied). 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.
    - toomuchtodo 13y ago
      ILS was not available on the SFO runway the Asiana aircraft crashed on ~2 weeks back: http://en.wikipedia.org/wiki/Asiana_Airlines_Flight_214 http://en.wikipedia.org/wiki/Asiana_Airlines_Flight_214
      - hedgie13 13y ago
        Yes, but the weather was clear. No need for ILS in such weather.
        toomuchtodo 13y ago
        Unless of course you've never landed at SFO before in an aircraft you're barely type-rated on.
        mikeash 13y ago
        Neither should matter. A visual landing at any airport is pretty much the same, and the basics don't change for different aircraft. There's nothing at all tricky about a visual approach into SFO.
- jnsaff2 13y ago
  You've got it backwards: CAT I is 200ft Decision Height (btw, not Minimum Descent) Cat II is 100ft Cat III is 0ft (with differing horizontal visibilities for IIIa/IIIb/IIIc
  - hedgie13 13y ago
    I am wearing paper bag for the rest of the day. Not enough caffeine in the morning.
bargl 13y ago
>Limitations Glide slope station for runway 09R at Hannover Airport in Germany >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.
- iliis 13y ago
  As always when this comes up: https://en.wikipedia.org/wiki/Battle_of_the_Beams https://en.wikipedia.org/wiki/Battle_of_the_Beams Yes, you can indeed hijack an ILS system. At least during WW2.
  - snom380 13y ago
    You can hijack it, but there are monitoring systems in place to detect if something is out of place. Also, ATC will usually notice flight path deviations quite quickly, at least on manned airports with radar coverage.
- yread 13y ago
  While ILS is generally considered to be the second most reliable instrument (after the windsock) it has its own problems... For example false glidescope, see http://www.ukfsc.co.uk/files/Safety%20Briefings%20_%20Presentations/Flight%20Ops%20-%20False%20ILS%20localiser%20capture%20BAE%20systems(1).pdf http://www.ukfsc.co.uk/files/Safety%20Briefings%20_%20Presen...
ceejayoz 13y ago
http://www.fastcompany.com/1266063/inside-next-gen-gps-based-airplane-landing-system http://www.fastcompany.com/1266063/inside-next-gen-gps-based...

mbrameld 13y ago

Do you have a source for aircraft flying using GPS alone? My understanding is that they rely on VOR and ILS systems.

mcguire 13y ago
http://www.faa.gov/air_traffic/publications/ATpubs/AIM/aim0101.html#aim0101.html.25 http://www.faa.gov/air_traffic/publications/ATpubs/AIM/aim01... (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.
VLM 13y ago
You can interpret that question a lot of different ways. 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.
fnordfnordfnord 13y ago
VOR system is on its way out. http://aeronav.faa.gov/content/aeronav/acfstatus/Presentations/11-02_Discontinuatoin_of_VOR_srvc-kward.pdf http://aeronav.faa.gov/content/aeronav/acfstatus/Presentatio...

eCa 13y ago

Considering how unreliable GPS altitude information is [1], I would like to not be on board when they do that.. For more information regarding what happens if someone alters the altitude of a plane, see [2]. [1] http://www.gpsinformation.net/main/altitude.htm http://www.gpsinformation.net/main/altitude.htm [2] http://www.imdb.com/title/tt0099423/ http://www.imdb.com/title/tt0099423/

asynchronous13 13y ago

> using GPS alone 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.