GPS Jamming/Spoofing Threat

[0TreeLemur]

Great article on the impacts of GPS jamming/spoofing here:   https://spectrum.ieee.org/aerospace/aviation/faa-files-reveal-a-surprising-threat-to-airline-safety-the-us-militarys-gps-tests

Of course the US Military must prepare for the threat. While our hardware detects outages, we pilots usually fail to detect spoofing events, and if well done our hardware doesn't detect them either.   In cruise I'll occasionally verify position by tuning in a nearby VOR and verifying that I'm on the correct radial.  However, doing a true position verification using two VORs is often not possible at the altitudes where I most often fly.

In preparation for potential operations in the MON  VOR world, having DME would be nice.  I've occasionally thought about installing a used DME.  What is the go-to model?  What about weight/power penalty?  Is installing DME worth it as backup nav data to GPS?

[toto]

Thanks for posting.  I read this yesterday and thought it was a nice summary of the issue.

The one time I encountered a GPS spoofing event was many years ago..  I realized that the view out the window disagreed hugely with the position displayed on two different GPS receivers (off by about 40 miles).  When I returned from the trip, I frantically searched for any NOTAM or reference to GPS testing or instability in the area and found none, though I did find a handful of other pilots complaining about problems in the same region on the same day.

I've been very curious lately -- with a recent GPS receiver that also does GLONASS, if the US military are testing/spoofing/jamming, is it possible to have the receiver prefer GLONASS over GPS when the two are in conflict?  Or is this just a bad idea all around? 

[Jerry 5TJ]

I suspect that intentional jammers are covering all the main GPS, Galileo, GLONASS and BeiDou frequencies.  

[toto]

9 minutes ago, Jerry 5TJ said:

I suspect that intentional jammers are covering all the main GPS, Galileo, GLONASS and BeiDou frequencies.  

Well, right, but I mean if it's just an unscheduled test - the inaccurate position event that I encountered seemed more like SA than a broad jamming approach.

[EricJ]

Some of the inexpensive USB GNSS chipsets can receive GPS(WAAS)/GLONASS/Galielo/BeiDou, so unless they all get jammed, you should be able to get a GNSS position.   I have one plugged into my Stratux, which feeds my EFBs, so, fingers crossed, even if the in-panel GPS unit loses integrity the EFB should still tell me where I am.   I've not been able to test this, though, so right now it's just expectation.  I think they likelihood that they'd all get jammed simultaneously is pretty low.

This is also why the VOR Minimum Operating Network is going to be important.   I'm working on multiple engineering projects that are motivated by making use of the MON more reliable for the times when it is needed.

 

[Mooneymite]

Everyday, there is GPS "testing" (actually jamming, in my estimation) as reported by NOTAMS in one, or more parts of the country.

Most of the time jets fly through the NOTAM'd areas without any indication.  However, sometimes the avionics starts giving warning messages and the EPU jumps way up.  Modern avionics relies on GPS for a lot more than just navigation.  We had 5 airplanes grounded when the almanac data became corrupted.  Even though these planes could navigate precisely laterally using IRS, DME/DME, rho/theta, and even DR, we couldn't fly 'em because so many other systems use GPS.  Pretty scary the degree to which we are dependent on something that was just a Gee Whiz 25 years ago.

[N201MKTurbo]

I kept my navcom and DME when I put in my fancy Avidyne. Some ask why I kept them. I flew IFR with them for 35 years. I can still fly IFR with them. I always keep them dialed in when I’m on an airway and most approaches. They give me confidence that I’m pushing the buttons right on the Avidyne. When I’m on an ILS, my eyes seem to gravitate to the needles rather than the G5, just out of muscle memory more than anything else. Anyway, If the GPS goes sideways, I’ll still get there.

[toto]

7 minutes ago, N201MKTurbo said:

I kept my navcom and DME when I put in my fancy Avidyne. Some ask why I kept them. I flew IFR with them for 35 years. I can still fly IFR with them. I always keep them dialed in when I’m on an airway and most approaches. They give me confidence that I’m pushing the buttons right on the Avidyne. When I’m on an ILS, my eyes seem to gravitate to the needles rather than the G5, just out of muscle memory more than anything else. Anyway, If the GPS goes sideways, I’ll still get there.

With an old VOR-based RNAV receiver, you could even fly direct using nothing but VORs.  

It's a little distressing how we've gone "all in" with satellite-based navigation.  People think of a moving map as synonymous with GPS, but the map just sits in a database and the GPS is just a position source.  Having that source be 10,000 miles away with a weak and relatively fragile signal seems kind of meh.  I'm a bit surprised that someone hasn't come out with a cheap pseudo-INS using a couple of accelerometers and a Raspberri Pi.  Having a purely local nav source feels like the ultimate backup, even if it's completely uncertified.

[N201MKTurbo]

3 hours ago, toto said:

With an old VOR-based RNAV receiver, you could even fly direct using nothing but VORs.  

It's a little distressing how we've gone "all in" with satellite-based navigation.  People think of a moving map as synonymous with GPS, but the map just sits in a database and the GPS is just a position source.  Having that source be 10,000 miles away with a weak and relatively fragile signal seems kind of meh.  I'm a bit surprised that someone hasn't come out with a cheap pseudo-INS using a couple of accelerometers and a Raspberri Pi.  Having a purely local nav source feels like the ultimate backup, even if it's completely uncertified.

I bet you could get a DSP based radio chip for a Raspberry Pi, that you could receive VOR signals and DME signals and calculate a position almost as good as a GPS. It could have a database of all the stations and switch between them rapidly taking cross bearings and DME fixes. With a little extra work, it could do the ADF thing on broadcast AM and FM stations, that would be a great backup.

Maybe I have a retirement job. I could get @EricJ to help, he is a radio genius, he kind of designed WI-FI.

[ragedracer1977]

I've had one 'real life' experience with GPS jamming.  Safety pilot and I were shooting approaches. I was shooting a GPS approach into KTYL.  There was a NOTAM for GPS outage, and we were on the edge of it.  I've got the needles centered, everything looking good.  I notice out of the corner of my eye, my safety pilot is looking outside and back at the instruments really quickly.  Usually he just sorta stares out the window, so I knew something was amiss.  The MDA was 300 AGL.  I get to the MDA, look up, and I'm at least 1/2 mile off the runway centerline.  I mean, not even close.  I was far enough off, there's no way I could have landed.  He just let it go, because he could see we weren't going to hit anything.  

We went missed and flew it again to the same result.  The GPS jamming did something to really screw it up. 

Edited January 23, 2021 by ragedracer1977

[Jerry 5TJ]

On 1/23/2021 at 5:19 PM, N201MKTurbo said:

..... I bet you could get a DSP based radio chip for a Raspberry Pi, that you could receive VOR signals and DME signals and calculate a position almost as good as a GPS.....

Easy enough to plug a SDR (software defined radio) USB dongle into a Pi.  Not hard to decode VOR signals.  A few lines of code...
DME involves transmitting a pulsed signal and listening for the ground station reply, that’s outside the capability of simple SDR sets.  
The accuracy would be nothing like a GPS derived systems.  But it works. 
Easier to buy a used KNS80 for a few bucks and install that venerable box. 

[N201MKTurbo]

2 minutes ago, Jerry 5TJ said:

Easy enough to plug a SDR (software defined radio) USB dongle into a Pi.  Not hard to decide VOR signals.  A few lines of code...
DME involves transmitting a pulsed signal and listening for the ground station reply, that’s outside the capability of simple SDR sets.  
The accuracy would be nothing like a GPS derived systems.  But it works. 
Easier to buy a used KNS80 for a few bucks and install that venerable box. 

You are correct about DME. But a cheap non GPS  position source would be cool. 

[Jerry 5TJ]

20 minutes ago, N201MKTurbo said:

You are correct about DME. But a cheap non GPS  position source would be cool. 

How about LORAN C? 

Oh, wait, the Coast Guard shut down the system a decade ago.  

[EricJ]

1 hour ago, N201MKTurbo said:

I bet you could get a DSP based radio chip for a Raspberry Pi, that you could receive VOR signals and DME signals and calculate a position almost as good as a GPS. It could have a database of all the stations and switch between them rapidly taking cross bearings and DME fixes. With a little extra work, it could do the ADF thing on broadcast AM and FM stations, that would be a great backup.

Maybe I have a retirement job. I could get @EricJ to help, he is a radio genius, he kind of designed WI-FI.

As mentioned, DME is not practical without a lot of FCC hijinks since it also transmits, but making a cheapie position substitute without GPS is one of the things I'm working on.   I only recently discovered that the approach I was going to take has recently been released in a basic sense as open-source software, so that's kinda nice. 

Getting a reasonable substitute if GPS gets jammed/spoofed is workable.   It won't be nearly as good as GPS, but a reasonable substitute when needed.

[EricJ]

1 hour ago, Jerry 5TJ said:

Easy enough to plug a SDR (software defined radio) USB dongle into a Pi.  Not hard to decide VOR signals.  A few lines of code...

It's a lot more than a few lines of code, but it isn't anything earth-shattering, for sure, and well within the capabilities of most decent SDR platforms these days.

 

[toto]

Just now, EricJ said:

As mentioned, DME is not practical without a lot of FCC hijinks since it also transmits, but making a cheapie position substitute without GPS is one of the things I'm working on.   I only recently discovered that the approach I was going to take has recently been released in a basic sense as open-source software, so that's kinda nice. 

Getting a reasonable substitute if GPS gets jammed/spoofed is workable.   It won't be nearly as good as GPS, but a reasonable substitute when needed.

It's a local position source?

[EricJ]

1 hour ago, ragedracer1977 said:

I've had one 'real life' experience with GPS jamming.  Safety pilot and I were shooting approaches. I was shooting a GPS approach into KTYL.  There was a NOTAM for GPS outage, and we were on the edge of it.  I've got the needles centered, everything looking good.  I notice out of the corner of my eye, my safety pilot is looking outside and back at the instruments really quickly.  Usually he just sorta stares out the window, so I knew something was amiss.  The MDA was 300 AGL.  I get to the MDA, look up, and I'm at least 1/2 mile off the runway centerline.  I mean, not even close.  I was far enough off, there's no way I could have landed.  He just let it go, because he could see we weren't going to hit anything.  

We went missed and flew it again to the same result.  The GPS jamming did something to really screw it up. 

That's not jamming, that's spoofing, and it's WAY worse than jamming.   If the signal was just being jammed or disappeared for some reason, you'd get a loss of integrity alarm from the receiver and you'd lose navigation information.   Good spoofing is much harder to do, but I think this is the sort of thing that the military plays around with for a lot of reasons.   It's bad because you get no indication, other than a NOTAM, that the signal might be being spoofed and might fly you somewhere other than indicated.

Jamming just results in a loss of signal and loss of navigation information, and the receiver can detect that.   Spoofing substitutes the actual signal for a fake one and if done properly you won't know it's happening.   It's bad news, so I'd suggest if somebody is doing an approach in an area NOTAM'ed for GPS interference to have an alternative radio navigation method up and cross-check them.

[EricJ]

5 minutes ago, toto said:

It's a local position source?

Yes, inexpensive, SDR-capable.   Effectiveness is completely TBD, but expectations are reasonable.

[jamesm]

Why not have an internal Nav like the airlines have ? The gyro's are getting cheaper.

[toto]

22 minutes ago, jamesm said:

Why not have an internal Nav like the airlines have ? The gyro's are getting cheaper.

Right, that's what we're talking about. The increasing reliance on satellite-based nav is unfortunate, especially since ground-based backup options are dwindling. I'd love to see someone come up with a cheap INS, whether it's based on some accelerometer thing or some breakthrough cheap LRG. But in any case have a local position source as backup would be nice. 

[PeteMc]

But as I understand it, ground based NAV aids are not going away.  They're just being reduced, maybe greatly reduced, but not eliminated. 

I just tried to find the report I had read a while ago, but I believe they're keeping enough of the High Powered VORs that you can still navigate the full US.  Granted you'll have to do the TO and FROM switch mid way, because there will not be enough VORs to always be flying TO.  But I have no plans to get rid of my ILS/LOC/VOR option any time soon as GPS can be messed with very easily.

 

[afward]

16 hours ago, N201MKTurbo said:

I bet you could get a DSP based radio chip for a Raspberry Pi, that you could receive VOR signals and DME signals and calculate a position almost as good as a GPS. It could have a database of all the stations and switch between them rapidly taking cross bearings and DME fixes. With a little extra work, it could do the ADF thing on broadcast AM and FM stations, that would be a great backup.

Maybe I have a retirement job. I could get @EricJ to help, he is a radio genius, he kind of designed WI-FI.

Funny enough, though I'm not an EE or radio guy I've previously looked into doing this.  Fractal antennas for ultra wideband coverage, FM & TV tower database with auto-ID (via RDS / ATSC header decode), VOR reception with auto-ID, Doppler calculations to aid in vector determination (and ultimately 3d position determination), etc...  SDR receivers would be required to make it work.  Interesting ideas, but ultimately I decided I didn't want to build a whole navigator.

One issue I thought of is frequency stability of the broadcast media antennas...  For that I figured I'd use three antennas and use differential phase to determine actual transmitted frequency and bearing to source.  Not sure that would've worked without antennas very widely separated, though.

That said, it would be interesting to see a navigator that supports multiple position sources...  then it would make sense to work on INS and terrestrial-broadcast position sources.

@EricJ probably has already thought of all this, though if not I'm good with the ideas being stolen.

[toto]

11 hours ago, PeteMc said:

But as I understand it, ground based NAV aids are not going away.  They're just being reduced, maybe greatly reduced, but not eliminated. 

Yep, that's right. FAA doesn't want to maintain VORs because they're expensive, but they have recognized the long term need for the high power network. (I think this largely covers enroute in the flight levels, but I'm not sure about long cross country flight down in the weeds.)

My airplane came to me with an enroute certified GPS+LORAN receiver, which had a nice built-in backup option. As long as you were high enough, the satellites could be jammed all day long and you could navigate with a ground-based system. But with LORAN decommed, GPS is it. And this unit is currently sitting in a box in my basement

I don't know if any of the major nav device manufacturers have incorporated a VOR-based RNAV function, but it would make a lot of sense. My perception is that today's flight students are very dependent on GPS, and are not very proficient at dead reckoning. If the nav box could just switch to a ground-based position source when GPS goes out, the pilot wouldn't need to do much but acknowledge the condition and then continue the flight (albeit with less accuracy) in an emergency fallback mode. 

[0TreeLemur]

23 hours ago, Jerry 5TJ said:

Easier to buy a used KNS80 for a few bucks and install that venerable box. 

Jerry- this is just the kind of input I was seeking.  What is the weight & power requirements for such a box?

Looking at the KNS80, its kind of tall for the amount of free space in my radio stack.   The KNS81 is thinner- Is that a good box too?  Looks newer.

-Fred

[PeteMc]

I have a KNS-80 that was recently pulled out.  Working fine when it was removed.