GPS Jamming Tests Frustrate Pilots, Controllers


Just as civil aviation has become thoroughly addicted to GPS, the military is trying to wean itself off that dependence and that’s causing some fractious conflicts in the Southwest. The military uses the wide-open spaces to purposely jam GPS signals to see how its equipment and personnel cope with the “GPS denial.” But according to IEEE Spectrum, the military and the FAA are not always on the same frequency when it comes to managing those tests and controllers and pilots have put their frustrations in writing in NASA’s Aviation Safety Reporting System. “Aircraft are greatly affected by the GPS jamming and it’s not taken seriously by management,” says one report gleaned by IEEE Spectrum. “We’ve been told we can’t ask to stop jamming, and to just put everyone on headings.”

The military does notify the FAA about jamming activity but that doesn’t always seem to get to the frontline workers in the system and the loss of GPS can be dangerous. One of the reports involved a business jet that made a wrong turn and ended up in the highly restricted airspace of the White Sands Missile Range, which, ironically, is the source of much of the jamming. Another pilot reported he lost his terrain mapping at a critical time and worried he’d end up in a smoking hole. When the jamming starts jamming up the system, controllers have the option to request a “stop buzzer” to get the military to turn off the electronic interference but some controllers complain they’ve been told not to make those requests and to just issue vectors to affected traffic. The FAA told IEEE Spectrum that controllers can, indeed, stop the tests if they think it’s necessary but those requests are automatically reviewed by upper management.

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  1. Satellite technology is too fragile to be considered the only means of navigation. Solar flares and solar mass ejections could conceivably knock out every satellite in orbit around the Earth; there just has to be ground-based legacy navaids available IN the aircraft, as a backup. And relying on controller-pilot communications are just as vulnerable to outages from solar events.

    • Yes.

      Updated Loran-C offers diversity of spectrum and physical location, so makes good sense. Proven stable and repeatable.

      Simple ADF might help find an airport in a pinch, but I am at best very wary of publishing lists of commercial radio stations as I wouldn’t trust the accuracy of the list. (Shutdowns, outages, antenna site relocation, ……)

      • The WAAS towers are supposed to be a kind of LORAN back up. No altitude information is valid (no GPS approaches), but a general location can be determined if in communication range of the WAAS or ADS-B towers. Remember these are limited by line of site and power.

        • ‘WAAS’ towers?

          WAAS signals from satellites only provide _corrections_ to increase accuracy of GPS signals.

          WAAS data comes from ground-fixed receivers scattered in the ballpark of a few hundred miles apart, that data is uplinked to special geo-stationary satellites who broadcast it for users. The data comes in GPS-like signals receivable by modified GPS receivers.

          (LAAS VHF signals come from ground stations near airports, that broadcast corrections to improve accuracy for precision approaches.)

          AEA might have primers on such.

          Bottom line is WAAS and LAAS are _not_ sources of position data alternative to GPS, they are supplements.

  2. Mac is right. We need redundancy. Because two of my based airports have discontinued terrestrial approaches (VOR-A and VOR 9/27) I finally upgraded the avionics to include a GPS IFR navigator. It’s nice, but the databases are expensive, and GPS can be very easily jammed over widespread areas with very little radiated power. LightSquared/aka Legato Networks clearly demonstrated this when they bought the GPS guard band frequencies claiming radio propagation physics is not what it is and disrupted a 1500 nm swath. Specific tests by the NBAA noted a complete loss of signal by the GNS430W. Lightsquared was ultimately denied its FCC waiver after every agency using GPS and the Aviation, Agricultural and Maritime agencies all protested. LS/Legato got what they wanted by big time contributions to certain political parties and they are at it again. The military has always been able to disable GPS at will because they own it. For years we argued and lost about the need for redundant systems. When the LORAN-C chain was shut down we lost that redundancy. It is a lot harder to jam LORAN-C signals, or an NDB carrier for that matter, yet we abandoned relatively cheap, highly cost effective redundancy. I may have the last airplane flying with an ADF on board, but I will keep my redundancy even if it is only to navigate to a broadcast station.

  3. Typical US Government – waste $10.00 to make fifty cents. Why don’t the mil spec check airmen (or whomever) just reach over and turn the f&*^g GPS off, like the rest of us do when practicing partial panel ? No need to jam the whole system to play dodge ball with the rest of us.

    • This is not a matter of someone getting a check ride. It usually involves multi-ship or even air/ground/space integrated exercises, sometimes even including elements (air and ground) from allied nations. These execises are critical to maintaining capability in the event of electronic warfare disruptions. As the Lightspeed experience shows, these signals are fairly easy to disrupt. Notification of the outage IS published well in advance of the exercise. Since, as a pilot, it is your RESPONSIBILITY to make yourself aware of all factors affecting your flight, as that pilot, you should make the effort to read the NOTAMs and prepare alternate means of navigation appropriate for that flight. VOR comes immediately to mind. Reduced, but still adequate coverage. Instrument approaches for some airports may not be available — but that is also part of your pre-flight planning.

      • “ Since, as a pilot, it is your RESPONSIBILITY to make yourself aware of all factors affecting your flight…”

        Which no one has the capacity to do. “All factors” means 100%. Nothing, especially in aviation, can be successfully measured/factored/counted at 100%.

        Like it or not, GPS has become the primary mode of navigation. Why in the world would one think it a good idea to flip a switch and actively, purposefully jam THE primary mode of navigation in the national airspace?

        Let’s shut down all the off-ramps on our interstates roadways for the next 300 miles…just to se how that plays out. Let’s turn off all traffic lights within a tri-state area….the general public would have a fit…but sure, taking down the primary mode of navigation? It’s OK!

    • The ‘whole system’ isn’t shut down for necessary military training. Frankly, civilian pilots should take the opportunity to practice their own GPS fail procedures. Any pilot who fails to cross check GPS signals might add that task to their instrument scan. Do we seriously believe our “friends” to the east and west will give us a heads up when (not if) they screw around with the GPS signal?

      The FAA’s decision to put darn near all of our eggs into the GPS basket is an underlying and fundamental flaw in our space based satellite dependent system design. Nextgen and the GPS constellation were meant to save money for the FAA and other operators of legacy ground based navigation systems. They were NOT intended to save you, me, or any other pilot/owner/operator anything but a little bit of fuel and a few minutes of flight time. But, we, like most pilots, fell for the marketing of convenience and supposed cost savings.

      If we (aviation users) are gonna lobby Congress or someone else to fix ‘the problem’, then let’s pick a solution (like a robust ground based system to seamlessly compliment GPS) to get behind that is much more robust than the faint satellite signals that are easily disrupted. Does anyone else recall that unclassified NASA study that implicitly advised AGAINST Nextgen/GPS? The NASA scientists catalogued at least four fatal vulnerabilities of GPS and Nextgen: Natural events such as sunspots; Intentional jamming (by China, Russia, NK, Iran, or any of our other ‘friends’); Spoofing (remember Iran has captured at least one US military drone by spoofing signals); and system design flaws. Additional vulnerabilities could be continued accumulation of space junk and intentional destruction of satellites.

      • You are correct. The FAA only decided to go GPS when they saw the cost savings. Oddly, someone (not me) got a huge check when they claimed it as their idea.
        When I first presented what is now ADS-B, not as a cost saver, but for better location accuracy, the idea was shot down, because of the weak signal factor of the GPS. The ground WAAS stations were supposed to augment the satellite signal issues. Oddly, WAAS was designed to increase altitude accuracy for precision approaches, but when the satellites are jammed, the altitude is what is missing even with ground WAAS stations. They will still give a pretty good location if you are within signal range of the ground stations. If you aren’t, they are of no use.

    • I work in the aerospace industry, and we can and do test everything by failing it with software, rather than actually having an external system bow to our wishes.
      Also, a CME could take out ground-based systems, as well.
      A hardened INS, periodically updated when GPS is confirmed to be legit, would be nice. I’m gonna bet it could be built for peanuts, perhaps some of the experimental guys can test it.

  4. Agree we need redundency but, the GA market made the decision years ago to go GPS. Many pilots have spent thousands of dollars to upgrade to GPS capable IFR capable avionics. I doubt the only solution to military exercises is jamming the entire system and expecting single pilots in IFR conditions to arbitrarily switch to plan B. I had an experience where GPS suddenly lost signal over the mountains in West Virginia last year. No emergency but definitely got my attention. There should be a compromise somewhere that leaves all parties functioning and comfortable

    • Well, for now you are required as a pilot to review NOTAMS… when pilots don’t, they can get themselves into a situation that may kill them. These include GPS jamming. GPS jam testing is why the FAA lets you use GPS for civil navigation. They were completely against GPS for legal navigation when I first approached them with the idea of not just navigation, but tracking planes for ATC.

  5. Surprised that with electronics so miniaturized that there is no inertial navigation apps available for the plethora of mobile devices we now have. I would like to work on such an animal, but the day job gets in the way. These devices can measure a person’s sleep cycle using the integrated accelerometer, so it might be able to provide navigation updates to a moving map. An INS app or device would provide autonomous navigation without the need for constant radio signals. Am imagining that GPS could be used, as an option, to set the initial/start coordinates, and occasionally update along the route to account for precession and other minor corrections needed.

    • I was a bomb/nav tech on both the B-58 “Hustler” and the B-52, et al. Accelerometers were the way the thing navigated with updates from other systems (Astrotracker, Doppler Radar, other nav signals) when available. Given today’s MEMS devices, I’d think that it’d be easy for one of the larger avionics manufacturers to come up with such a system as a backup running off of GPS, as you opine. The problem would be that if you fear a CME or nuclear event, unless they’re hardened (translated, drives up cost), they’ll get cooked. Same thing with all the modern cars filled with electronics. Your Tesla … fugnetaboutit. My ’53 Chevy will be the only one running.

      I bought an airplane that had a Northstar LORAN in it and I loved it prior to decommissioning of that system. It was a GIANT mistake to decommission it.

  6. I have encountered GPS jamming several times, some times while over the ocean. The most recent was about two years ago as I was flying from the San Antonio area to Sacramento and was approaching Albuquerque. I had seen the NOTAM and was flying airways so as to make the transition to VOR navigation easier should the need arise. The GPS gave a RAIM alarm and dropped off line. I felt very smug as the airliners started whining to Center about navigation failure. Then I found that the Gallup VORTAC was down. I had no choice but to ask Center for a vector. No big deal at FL210 as I wasn’t likely to run into anything or anybody but still …

    GPS is fragile and no panacea. It is worthwhile to ask not how something works, but rather how something fails, and what can one do in that case.

    • That VOR being down should have been communicated through the FAA’s maintenance Control Center, MCC. I worked in there, unfortunately like controllers, the people making those decisions are not pilots and some are not certified on all the systems. So, they don’t all have a good understanding of what should and what shouldn’t be shut down for maintenance, or in this case testing of GPS jamming.
      I hope you immediately notified ATC to warn them the test needed to be shut down. ATC can in this situation direct the jamming to be turned off. It may take a few minutes though, because of the communication required. A lot can happen in a few minutes. 😳

      • “…unfortunately like controllers, the people making those decisions are not pilots and some are not certified on all the systems. So, they don’t all have a good understanding of what should and what shouldn’t be shut down for maintenance….”

        In my recent experience flying IFR without a GPS, I’ve found ATC will vector me to VORs that are NOTAMed out-of-service. Or clear me to fly Tango routes or “go direct” when I’ve filed “/A” (no GPS). Sometimes just picking up a clearance prior to take-off will have the same errors.

        [After some back-and-forth with clearance delivery (who was also the ground- and tower-controller) while trying (and failing) to fix the problems in the flight plan, the harried controller replied, “just take off and sort it out with departure.”]

        I’ve found the same problems when using the FAA’s site to plan and file. I’ll set the departure and destination airports, select the VOR planning option and the site will helpfully provide with me with a VOR-to-VOR route. Except checking the NOTAMs will often show several of those NOTAMs out-of-service. Clearly the flight-planning software just plays connect-the-dots without regard to what’s actually working or whether or not TFRs are in the way.

        With the reduction of VORs as the FAA heads towards it’s “Minimum Operational Network”, the remaining VORs become even more important. For instance, if the YORK (YRK) VOR in Kentucky were to go out-of-service, it would leave a large hole to navigate around.

        eLORAN would be a great backup. And/or a modern digital panel-mount INS. The former would require government funding. The latter would be an effective “user fee” to continue safely using the NAS. Guess which one the FAA would choose?

        • I have had a similar experience. When I first purchased a share in a Cherokee Archer, we didn’t have an IFR GPS and I had to fly in the system with VOR. Even with /A, I had to tell every controller I spoke with that I can’t go direct to anywhere but a VOR.

  7. This type jamming was the main concern by both the Department of Defense and the Department of Transportation when I presented the idea to move to GPS location auto responder over the radar based transponder in 1989. The radar based interrogators are very hard to jam in all directions so only a few transponders are effected in a jamming situation. The jamming venerability is why it took almost 30 years for what is now called ADS-B. The tests by the military are currently being done in areas where there is the least effect to navigation. This test jamming will continue for the foreseeable future.

    • Accelerometers were standard in Inertial Navigation Systems, which is probably what you had. Integrate acceleration to get velocity, then integrate again to get distance.

      Superseded for many people by ‘ring laser gyros’ which measure velocity, integrate to get distance. Newer/smaller RLGs use fiber-optic path for the light whose shift is measured.

      Both subject to drift, want updating somehow.

      With star-tracking systems sometimes, presumably absolute position measurement but challenge is positive identification of starts.

      Another matching system, i.e. match observation to known geometry, is navigation by downlooking radar against terrain. USAF were testing it for cruise missiles down the McKenzie River in Canada because terrain characteristics like tundra are similar to the USSR.

      ‘Doppler’ is radar, four beams reflecting off the ground, antenna rotated to balance signals to get track angle. Very common before INS became readily available. Can that be miniaturized?

  8. My Aera 660 uses GLONASS which can be turned off if you suspect it is corrupted. Don’t know if there’s internal software to give a warning if it detects a difference in position between our GPS and GLONASS?

  9. Yes, the GPS databases are needlessly expensive, and seem to be needed to be refreshed if the destination airport changes anything that may not be important, eg a logo. Airport approaches are rarely changed, but you still have to do an upgrade. Perhaps there should be a private pilot database that keeps the basic info but is locked in for 3 years. Or should Govt get involved in database charts, as all the info comes from them anyway

  10. I use GPS on essentially every flight. But it’s a supplemental Nav system. The signal we receive is incredibly fragile. I cringe every time I see the FAA snuffing out yet another VOR. And I’m equally concerned when I give a BFR or IPC and the pilot can’t locate themselves using VOR’s. We need to maintain a redundant, independent terrestrial based Nav system.

  11. The huge cost-performance advantage of GPS was (and is) irresistible, so it’s no mystery why the decision was to go with it despite it’s known downsides. Ditto the decision to maintain only a basic skeleton VOR network and radar as backups. I think both decisions were entirely reasonable.
    As far as jamming is concerned, no question the military must realistically challenge its people with “OK, GPS just went down, what are you gonna do now?” Civilian pilots can benefit from being tested by briefly facing the same challenge. It actually is possible to shower even when there is no hot water, and there ARE other ways to navigate.