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In the U.S., the Department of Defense along with other Federal Agencies of the Government operates & maintains the GPS.

In the rarest of the events, if for any reason whatsoever, the Government decides to shut off GPS provisioning (even temporarily), what are the consequences/alternatives for the aviation industry?

  1. What percentage of the industry solely relies on The GPS to operate?

  2. What percentage of the industry has enough alternative navigation means to continue operation regardless The GPS?

On a broader spectrum, I'm also curious about the aviation industry's reliance on GNSS and what could happen in cases of global disaster, wars, cyber-wars etc. (all of which are not impossible).

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    $\begingroup$ GPS is unavailable regularly because of military testing or other reasons. There are GPS NOTAMs to inform pilots. $\endgroup$ – Pondlife Sep 28 '17 at 2:30
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    $\begingroup$ The American GPS is not the only GNSS system in the world. See en.wikipedia.org/wiki/GLONASS or en.wikipedia.org/wiki/Galileo_(satellite_navigation) or en.wikipedia.org/wiki/BeiDou_Navigation_Satellite_System $\endgroup$ – J. Hougaard Sep 28 '17 at 5:53
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    $\begingroup$ @RaajTram Those systems also cover the U.S. The problem is that in a crisis where turning USGPS off is reasonable, it's likely those other civilized nations will also cooperate by shutting theirs off. $\endgroup$ – Harper Sep 28 '17 at 16:06
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    $\begingroup$ @Pondlife: GPS is not "unavailable regularly". That is complete nonsense. Individual satellites periodically undergo maintenance, and some ground-based auxiliary services might periodically undergo maintenance. But the GPS constellation as a whole has been operating uninterrupted for decades. When half the constellation temporarily reported the wrong UTC correction in January 2016 it was deemed a hugely disruptive and unusual event. Besides, the military signal is different from the civilian signal and you are never using it (for one, it's encrypted so that you can't). $\endgroup$ – Lightness Races in Orbit Sep 28 '17 at 23:25
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    $\begingroup$ @LightnessRacesinOrbit You're correct that GPS is not regularly turned off. On the other hand, it is regularly unavailable for air navigation use in specific areas in the US, usually because of military interference testing. As a pilot, hearing that "GPS is always available, you just can't receive it sometimes" doesn't help me much; as a practical matter, the DOD regularly decides to make GPS unavailable in defined areas. Hence the need for GPS NOTAMs. I don't know if that fits your definition of "unavailable" or not. $\endgroup$ – Pondlife Sep 29 '17 at 12:27
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If the GPS is unavailable, it will be quite an impact to the aviation industry.

All airliners in-flight will experience degraded RNAV performance, but they would make it to the destination using VORs, DMEs and ILSs. For general aviation, things are not so lucky. The GPS display provides an excellent situation awareness in small aircrafts; without it, navigation reverts to old school VFR and reading charts. Most pilots will probably make it, but a few may get lost and end up in fuel exhaustion.

For airliners preparing for departure, initiating the INS is time consuming as the GPS coordinate is used as one of the startup parameters. The coordinates of the gates can be looked up in airport charts, some airports also have signs which specify the GPS location; both of these take longer time. Suddenly, pilots flying oceanic routes find out they need more planning for contingencies. Some routes may be changed to fly VOR-to-VOR. Departures around the world are going to be delayed, that is for sure.

Ground Proximity Warning Systems, which use GPS to determine the aircraft's location, are unable to use their terrain database to provide warnings to pilots, although warnings based on radar altimeters should still be available.

Basically, we are thrown back to the 80s or 90s, when GPS was not yet widely adapted. Many of those navigation aids are still in use today, so the industry can still fly, but traffic capacity will be reduced.

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    $\begingroup$ ”Basically, we are thrown back to the 80s or 90s...”. So, new Embry Riddle Graduate Pilots won’t get jobs? What else is new? $\endgroup$ – RaajTram Sep 28 '17 at 13:38
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    $\begingroup$ Well, there's always ATC. "Help, I'm lost, what's my position?" $\endgroup$ – GdD Sep 28 '17 at 14:17
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    $\begingroup$ With the current VOR deprecation schedule, falling back won't be viable for much longer. It's marginal already... $\endgroup$ – Brian Knoblauch Sep 28 '17 at 14:58
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    $\begingroup$ What is a GPS coordinate and how does it differ from geographic coordinate, INS coordinate or GLONASS or Galileo coordinate? $\endgroup$ – Vladimir F Sep 28 '17 at 17:20
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    $\begingroup$ Dude, no. Pilots are trained for this. It's a slight inconvenience because direct-to routings and GPS-only approaches are unavailable, but if you get lost without GPS you have no business operating a plane. $\endgroup$ – Simon Richter Sep 28 '17 at 19:08
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There are going to be bigger issues. The shipping industry is GPS reliant, the communications industry heavily relies on GPS time signals, Routing for trains, and so on. The fact is that the chaos without GPS will extend far beyond aviation. It will impact the network, the power grid, agriculture, mining, and so on.

In 1992, I had a team which proposed a smaller aircraft launched GPS system in LEO to handle such an emergency. For the most part, receivers could use the LEO transmitters.

But if I were just worried about aircraft, then I would also have GLONASS, Galieo, and others integrated into the receivers. I believe many receivers are currently configured to handle GPS and GLONASS concurrently, and employ WAAS, and the European, Japanese and Indian augmentation systems as well.

Things are changing, because I recently found a GPS/GLONASS receiver with WAAS and the other equivalents, with a USB interface, for $18. Pretty amazing.

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  • $\begingroup$ This raises a question - would it be wise should ALL the GPS receivers be manufactured such that they accept GPS signals from all the global GNSSs? $\endgroup$ – RaajTram Sep 28 '17 at 23:33
  • $\begingroup$ Depends upon your market. Or are you thinking legislatively? $\endgroup$ – mongo Sep 29 '17 at 1:39
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    $\begingroup$ @RaajTram: Russia already demands GLONASS (can't sell pure GPS there) and Galileo is designed to be highly GPS(NavStar) compatible. The Chinese, Japanese and Indian systems are not global. $\endgroup$ – MSalters Sep 29 '17 at 7:05
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Currently IFR capable aircraft are required to retain VHF navigation radios for use with terrestrial navigation beacons. These can work with existing RNAV systems as well.

Other options for navigation from a failure of the GNSS service can include the following.

LORAN - still popular with maritime operations, LORAN is still a very accurate means of navigation. Unfortunately aviation LORAN receivers fell out of favor with the advent of GPS.

Inertial Navigation Systems - current generations of solid state INS gear are highly accurate but accuracy begins to degrade with prolonged use, requiring accurate position updates from time to time.

Celestial Navigation systems - electronic sextants which can track known stars in the sky. The systems can be combined with other INS and RNAV systems for improved performance and redundancy.

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    $\begingroup$ +1, but can you cite a FAR or other reference for the claim in your first sentence? IIRC the only requirement is equipment suitable for the route to be navigated. $\endgroup$ – pericynthion Sep 28 '17 at 5:19
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    $\begingroup$ There are a few working LORAN transmitters worldwide, but just a few... Probably too few to give a planetary coverage... $\endgroup$ – xxavier Sep 28 '17 at 7:59
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    $\begingroup$ LORAN was officially shut down back in 2010... $\endgroup$ – Brian Knoblauch Sep 28 '17 at 15:00
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    $\begingroup$ According to the AIM (US) your first statement is incorrect. "Aircraft using [un-augmented GPS] for navigation under IFR must be equipped with an alternate approved and operational means of navigation suitable for navigating the proposed route of flight." "WAAS avionics are evaluated without reliance on other navigation systems. As such, installation of WAAS avionics does not require the aircraft to have other equipment appropriate to the route to be flown." As a practical matter, I doubt that there are any aircraft that are GPS/WAAS equipped that do not also have the ability to use VORs. $\endgroup$ – JScarry Sep 28 '17 at 15:04
  • $\begingroup$ No VHF Navigation Radios are required for an IFR capable airplane with or without GNSS equipment aboard. $\endgroup$ – Carlo Felicione Sep 28 '17 at 20:38
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In the past, the US GPS system incorporated Selective Availability (SA), this ensured civilian users has less accurate positioning than the US military. SA was switched off in 2000, and since 2007, new GPS satellites do not have the option to switch on SA.

If the US military needs to degrade GPS service, it'll be done in a limited region. Presumably that region will be a warzone, and will be closed to commercial and general aviation anyway.

If the US ever has to switch off the entire GPS system, WW3 has probably broken out. Again, navigation won't be the biggest problem for commercial and general aviation in this scenario.

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I am not sure about the current distribution in the market, but the value of other constellation owners like GLONASS or Galileo would suddenly increase. Currently, due to wide usage of GNSS they aren't getting much traction. In fact, the majority of cellphones currently have both GNSS/GLONASS available. In fact, Russia poses additional tax if a device doesn't have GLONASS support to increase the usage of GLONASS. So the only thing I see is a sudden bump in usage of other constellations. My iPhone/Samsung phone would be just fine!

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  • $\begingroup$ Aviotion does not really use phone satnavs. $\endgroup$ – Vladimir F Sep 29 '17 at 5:50
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    $\begingroup$ @VladimirF: GPS receivers these days use specialized chips to convert the radio signals into longitude/latitude/height coordinates. Further processing will differ between applications (such as navigation), but it's this first chip which will handle GLONASS and Galileo. $\endgroup$ – MSalters Sep 29 '17 at 7:07

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