GPS And ADS-B Problems Cause Cancelled Flights

Something strange has been going on in the friendly skies over the last day or so. Flights are being canceled. Aircraft are grounded. Passengers are understandably upset. The core of the issue is GPS and ADS-B systems. The ADS-B system depends on GPS data to function properly, but over this weekend a problem with the quality of the GPS data has disrupted normal ADS-B features on some planes, leading to the cancellations.

What is ADS-B and Why Is It Having Trouble?

Automatic Dependent Surveillance-Broadcast (ADS-B) is a communication system used in aircraft worldwide. Planes transmit location, speed, flight number, and other information on 1090 MHz. This data is picked up by ground stations and eventually displayed on air traffic controller screens. Aircraft also receive this data from each other as part of the Traffic Collision Avoidance System (TCAS).

ADS-B isn’t a complex or encrypted signal. In fact, anyone with a cheap RTL-SDR can receive the signal. Aviation buffs know how cool it is to see a map of all the aircraft flying above your house. Plenty of hackers have worked on these systems, and we’ve covered that here on Hackaday. In the USA, the FAA will effectively require all aircraft to carry ADS-B transponders by January 1st, 2020. So as you can imagine, most aircraft already have the systems installed.

The ADS-B system in a plane needs to get position data before it can transmit. These days, that data comes from a global satellite navigation system. In the USA, that means GPS. GPS is currently having some problems though. This is where Receiver autonomous integrity monitoring (RAIM) comes in. Safety-critical GPS systems (those in planes and ships) cross-check their current position. If GPS is sending degraded or incorrect data, it is sent to the FAA who displays it on their website. The non-precision approach current outage map is showing degraded service all over the US Eastern seaboard, as well as the North. The cause of this signal degradation is currently unknown.

What Hardware is Affected?

GPS isn’t down though — you can walk outside with your cell phone to verify that. However, it is degraded. How a plane’s GPS system reacts to that depends on the software built into the GPS receiver. If the system fails, the pilots will have to rely on older systems like VOR to navigate. But ADS-B will have even more problems. An aircraft ADS-B system needs position data to operate.  If you can’t transmit your position information, air traffic controllers need to rely on old fashioned radar to determine position. All of this adds up to a safety of flight problem, which means grounding the aircraft.

Digging through canceled flight lists, one can glean which aircraft are having issues. From the early reports, it seems like Bombardier CRJ 700 and 900 have problems. Folks on Airliners.net are speculating that any aircraft with Rockwell Collins flight management systems are having problems.

This is not a small issue, there are hundreds or thousands of canceled flights. The FAA set up a teleconference to assess the issue. Since then, the FAA has issued a blanket waiver to all affected flights. They can fly, but only up to 28,000 feet.

This is a developing story, and we’ll be keeping an eye on it. Seeing how the industry handles major problems is always educational, and there will be much to learn in the coming days.

80 thoughts on “GPS And ADS-B Problems Cause Cancelled Flights

      1. 1992 U.S. National Radionavigation Plan called for shut down of Loran-C. However, U.S. Coast Guard had just finished getting Loran-C installed on all its ships so the shut down was postponed for about 20 years. I was sad to see it go for the very reason that it was so repeatable and would reveal when GPS was being spoofed and slowly being pulled away from what it should report (somewhat like the plot of the James Bond movie “Tomorrow Never Dies” (1997).

          1. Replying to myself to add: I say “GNSS” and not just GPS because these problems are common all satellite-based systems. Just because the problems discussed in the article are GPS and ADS-B specific doesn’t mean other systems can’t be / aren’t affected.

    1. As a navaid engineer, it’s good news for me.

      Of course they’ve been saying goodbye to navaids since the 90’s, and yet we’re still putting them in all over the place.

      Nothing moves fast in aviation, and a hiccup (minor or otherwise) can set the process back decades.

    1. Could be something as mundane as a satellite malfunction or something as nefarious as a state level attack to see how much disruption they can cause. I doubt that it’s ground based given the affected area, but I’m sure some three letter agencies are all over this.

      1. RAIM is the older integrity monitoring and prediction system. WAAS is the newer, higher precision system with its more advanced integrity check.

        This isn’t a simple matter of routine degradation. WAAS accuracy has been compromised. WAAS is the basis for ADS-B. Without WAAS accuracy, the reported traffic location can’t be trusted. It’s the Achilles heel of the new ADS-B collision avoidance system.

  1. Thanks, hackaday. Info much appreciated. I have spent the last 7 1/2 hours on this since my grandson’s flight itinerary to come visit me was canceled. Now implementing a new plan.

    1. The last leap second was the very end of 2016. Other than that, not sure what you mean by leap minute.
      Also GPS isn’t adjusted for leap seconds at all, and is already quite a few seconds ahead of UTC

    2. There was a GPS 2019 Week Rollover back in April 6, 2019. This would have had the same effects as the Y2k bug, but for GPS-based systems.
      Since specific systems/aircraft seem to be affected (the article cited Bombardier CRJ 700 and 900), I tend to think the cause is related to firmware updates than actual GPS system degradation.

  2. The RAIM degradation is normal, that is why the RAIM prediction map is published. See: https://flyingandtechnology.blogspot.com/2014/06/raim-and-gps.html. That particular map is only for aircraft with pre-WAAS GPS receivers without barometric aiding. The red areas probably mean the vertical guidance is most affected, so the service should not be used for any approaches, but is good enough for normal navigation.

    There is also another radio system for Smaller GA aircraft (think Cessna’s and such) called UATs. That can be used. My page that covers the table of people who need what ADS-B systems: http://flyingandtechnology.blogspot.com/2013/10/uat-or-1090es.html.

    It is getting bad, like B-717s and 737s are also being affected.

    Yikes!

  3. Would the first 60 satellites of Starlink currently be travelling from their initial orbit ~450 km to their final orbit ~550 km using ionised krypton thrusters right now ? Could the ionised krypton gas trails generated attenuate signals at GPS frequencies ?

    https://hackaday.com/2019/05/31/see-starlinks-space-train-before-it-leaves-the-station/

    It is probably totally unrelated but it would take a while to raise their orbit height by 100 km (~62 miles). I think that this is the first deployment using krypton gas (xenon gas was used up until now, but is more expensive).

    1. Being ion thrusters they’re not kicking out that much Krypton. Unlikely.

      How are XM and Sirius radio doing? They’re in the same band and sirius sats were low earth orbit as I recall.

  4. We shouldn’t mix up two things. GPS isn’t ADS-B, and that map is only the RAIM prediction. I think the spam filter keeps eating my posts. Google RAIM prediction to get to the FAA RAIM prediction web site.

    I have a couple posts about RAIM and GPS and ADS-B on my blog (flyingandtechnology.blogspot.com).

    The trouble is most likely the FMS software on particular models. It could also be that they are C-129 level (pre-WAAS) GPS units and the weather is bad enough that the aircraft need to fly GPS approaches, but the RAIM prediction won’t let ’em

  5. Wow, I didn’t know we can’t have normal commercial flights without GPS. That will be a mess if a G5 conflict ever goes hot.
    Come to think of it, my tractor won’t plant without a GPS signal. I could disable that though.

      1. Big planes can get by just fine and dandy completely without GPS, because they can afford to have expensive inertial navigation as a backup.
        Problem is if the ADS-B transponder aboard said planes can use the data from their inertial navigation systems and of course there’s reduced accuracy compared to GPS, especially for long flights because gyros drifting out of position is not a flaw but a feature…

        But if SHTF and there would be no satnav of any kind, modern vibrating structures gyros are up to the task, they cost a lot more.

  6. The airline I work for is having this issue. The story we’re getting is that at approximately 3:00z on 6/9/19, the WAAS system on all of the GPS satellites received a software upgrade and that the software upload was somehow corrupted. This means that aircraft equipped with the WAAS MMR’s (Multi mode receivers) manufactured by Rockwell Collins are unable to resolve the WAAS signal from the satellites, thus causing MMR and GPS failure messages in the aircraft. The aircraft equipped with the pre WAAS MMR’s are not affected. Our airline is working with Rockwell Collins, the aircraft manufacturer and the FAA to receive permission to return our aircraft back to the pre WAAS configuration until the WAAS systems on the satellite constellation are operating normally again.

    1. “the software upload was somehow corrupted”

      That’s terrifying. It suggests that the satellites’ update system isn’t encrypted or signed. So you might be able record the transmission and replay it with intentional errors to brick satellites.

      I hope they actually mean “we pushed a buggy release and are going to blame it on transmission errors to save face.”

    2. “[…] the WAAS system on all of the GPS satellites received a software upgrade […]”

      While the WAAS system collect data transmitted from the GPS satellites, it does not transmit anything to or through the GPS satellites. Instead WAAS uses several geostationary satellites to transmit the corrections.

      https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/waas/howitworks/

      https://en.wikipedia.org/wiki/Wide_Area_Augmentation_System

  7. The main purpose of ADS-B is to send the plane’s identification and flight level. GPS data is just a “nice to have” addon. Many planes don’t send it anyway so this is nothing anyone would rely on. As the problem seems to affect some devices only, it’s likely that they probably have some kind of bug that prevents them from sending any ADS-B information at all if they can’t get a GPS lock (just a wild guess)

    1. The ADS-B sends the plane’s 3D position, identification, and speed. WAAS GPS is mandatory for determining the aircraft’s position. What may have lead you to believe it’s an add-on is that, when installing ADS-B, if your aircraft doesn’t already have WAAS GPS, then you must add it as well. For existing WAAS equipped aircraft, the newly installed ADS-B will use your existing WAAS GPS information.

    2. No. This is what “Mode C” SSR does. ADS-B position reports is sent by most larger aircraft, and is in fact mandatory in many countries. Entire airspaces (for instance, large parts of Canada) are dependent on ADS-B (or sometimes -C) for ATC.

      ADS-B mainly uses ‘ships position’ for larger aircraft. This means that ADS-B positions are usually FMC positions; positions that MAY be augmented by GPS position information, but it is in many cases augmented by DME/DME updates (strategy may vary per aircraft or airline). This means that loss of GPS information may not pose such a big problem for ADS-B. Again, this is dependant on aircraft type and system design; for smaller aircraft that use GPS as their sole navigation source, ADS-B reporting will stop working altogether when GPS fails.

      Also, TCAS uses ADS-B position reports to display aircraft further away on nav-displays (uses different air-to-air interrogation for shorter range collision avoidance, not dependent on ADS-B)

  8. So what is this “GPS degradation” and why does it even affect those airplanes?
    Even my EUR150 phone has GPS, Glonass, Galileo, and maybe some other localisation soft/hardware.

    but from that Boing MAX debacle (Which would never have gotten FAA approval 20 years ago) it seems that putting in a little bit of redundancy is too much to ask.

    Fukushima is also exactly the same, Is it really that difficult to figure out it’s not smart to build nuclear power stations in a pit on the coast in a known tsunami sensitive area?

    It’s time “those engineers” stop behaving like naive 4 year olds.

    1. Thinking the old school LORAN system needs to be up and running also. Why not? Doesn’t it cost enough or something for those rich fat cats?

      Exactly why the need for floating or, even better, underwater thermonuclear power plants. Ideally desalinating water while they’re at it to mine the water and purify. If not processing the water… I’m thinking high pressure external combustion instead of steam turbine generators/alternators too. Crazy not to take advantage of the underground capabilities in my opinion. Can mine out some mineral maybe and have a minimum overlay to cover up the facility too. Just plain lazy bums. Amazing how some plants make millions a day.

  9. “It’s time “those engineers” stop behaving like naive 4 year olds.”

    False notion. All of these are because cost-cutting managers above engineers decided to maximize short-term profit. That’s the reason they exist.

    None of them of course will take the blame when something goes wrong, as we’ve seen in case Boeing, but blames engineers, who weren’t asked at all.

    None of these are engineering problems, but pointy haired boss-problems.

    1. Ah, managers…
      Like that overly expensive space box that fell out off the sky because of some faulty O-rings.
      Those O-rings never should have been there in the first place, just a straight piece of plating is much more efficient, but the managers decided that everybody had to earn some money on the thing, which was therefore bolted together from far too many pieces.

      The engingeers made noise like thunder and lightning, Managers shug their shoulders.

    1. Did some reading in between.
      GPS is a pretty weak signal to begin with, but also:
      A defective TV broadcast station had been found (unrealted) which leaked too much into the wrong frequencies.

      It also seems that lots of people are walking (driving) around with GPS jammers becasue they do not want their position to be recoderd continuously.

      1. Yeah, that would be my first choice if I didn’t want to draw attention to myself, a continuously broadcasting beacon on a frequency that I’m not allowed to use. /s

      2. No, look at the region covered. It’s roughly the eastern third of the U.S. and up into Canada. I’m not even sure a high-flying aircraft could generate that wide of a disturbance. If it’s man-made, it’s a satellite. I suspect others are right and it’s a solar storm. Of course, that’s not good news. There will always be solar storms.

  10. “GPS systems (those in planes and ships) cross-check their current position. If GPS is sending degraded or incorrect data, it is sent to the FAA who displays it on their website.”

    How is this data sent, and where did you find the fact associated with this?

  11. It matters not. Search and beacon radars are not affected. Although there was a recent modification to the GPS receivers on the ATCBI-6 beacon radar system. Things that make you go Hmmmmmmm…………………………………

  12. A Chinese Long March-11 rocket launched 7 satellites from a platform in the Yellow Sea off Shandong Province on June 5, 2019. It launched “two technology experiment satellites and five commercial satellites into space,” according to China Central Television (CCTV).

    Those “technology experiment satellites” might be worth looking into.

    1. This particular issue is directly related to certain GPS units from Collins Aerospace (formerly Rockwell Collins). A software design error resulted in the system misinterpreting GPS updates due to a “leap second” event. Collins has advised its customers to not power on the units until June 16, the next scheduled update by the US government to the GPS constellation.

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