GPS Spoofing Raises Alarms - AVweb

experiencing complete navigation system failures because the hacker replaces the position data beamed by the GPS signals with false coordinates. “[Twelve] separate reports have been now received by OPSGROUP, and in most cases the [Inertial Reference System] becomes unusable, VOR/DME sensor inputs fail, the aircraft UTC clock fails, and the crew have been forced to request vectors from ATC to navigate,” the site reported.

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To interfere with aircraft the spoof signal has to come from above the aircraft

It’s quite a statement to say ‘Someone in the Middle East’ figured it out. It’s not actually very difficult to arrange the signal timings with gear that has been around for a decade or two and costs a few dollars. At least as far as I can ascertain. The trick is to get the receiver to prefer ‘your’ emissions to ‘theirs’. I’ve got hardware which is supposed to be able to do it with script-kiddie class understandings of the technology. Have not tried this trick/experiment. Yet. If/when I do, it will probably be in a Faraday cage or heavy shielding with low powers so it only impacts my phone.

Note that this is not very related to the AIS stuff. In the AIS case one replaces inputs from the GPS unit with data of one’s choosing then transmits the bogus data. In the case of this thread, one makes the GPS unit itself spit out invalid info. At least that’s my understanding of things, but again, I’ve yet to monkey with it.

It’s interesting to note that when I first got interested in this stuff about 20 years ago, the (purportedly) U.S. intelligence agencies were so freaked out about FPGAs (Field Programmable Gate Array chips) that they were trying to get them outlawed, or at least controlled. Not very practical to do thankfully (for us enthusiast types.)

Haven’t looked into this, but seems strange that GPS spoofing would render the inertial nav system unusable…since the reason behind the inertial nav system is to not require outside input.

Prior to the GPS constellation, INS was a stand-alone system but it now uses GNSS to prevent degradation. I’m guessing that the introduction of satellite information would provide an entry from which the INS readouts could be corrupted.


Don’t know anything about it. I googled James Reason’s term “tightly-couple” in this context and got some papers on the subject: gnss gps inertial navigation “tightly coupled”

The impression I got from a quick scan is that if the system is tightly-coupled it will continue to be reliable in the case of certain expected failures such as lost, weak GNSS or multi-path signals. Perhaps such systems fail against spoofing, or evidently did in this case.

Edit: Evidently the system is protected to some degree against spoofing but in this particular case the spoofing was more sophisticated and that protection failed.

The designers of these systems sometimes interconnect them in ways that are not obvious and not very smart in retrospect. I think the INS sees itself suddenly becoming “60 miles off course” and decides that the INS must be defective. They must not have thought about the GPS being the defective piece of the puzzle.
One suite of avionics would TOTALLY become useless, even the basic attitude instruments, if it lost GPS lock. That was a nasty and unexpected surprise. This is partly why Air France flew a perfectly good airplane into the ocean, when the displays start going nuts it isn’t always easy to figure out which ones are still good.
Back to boats, if you suddenly had a cross-track error of 60 miles, would your autopilot:
A. Disconnect
B. Disconnect and alarm
C. Go hard over to try and get back on course
D. Go hard over to try and get back on course and alarm
E. Display a screen offering an extended warranty

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The article in the OP links to this one which is better and more in-depth.

  • This type of GPS spoofing has not been seen before – IRS is quickly “infected” by false position

In the Baghdad FIR, the crew of a 777 enroute were essentially forced to ask “What time is it, and where are we? “. Almost all incidents we’ve seen result in requiring ATC vectors to navigate. Clearly, in the areas that these events are occuring, this is disconcerting.

They put INS on DP vessels for GPS failures but the other thing INS does very well is tell you when the gps is wrong, thats very easy as its based on acceleration.
If you had to accelerate at 5g to get to your new position I think the software would reject that
My guess is aircraft assumed being up in the air they would have very little gps issues?

I wonder if this issue is plane in wrong place or the ads-b saying it is?

ADS-B/AIS says you are where the GPS says it is. If the GPS signal was spoofed 60 miles off, ADS-B/AIS signal would also be 60 miles off.
One difference is most airplanes use the same GPS to drive everything while many (maybe all?) AIS units have their own GPS unit internal to them.

What I got was while a GPS outage was taken into consideration, the GPS just being wrong was NOT.

I had a Garmin GPS (GPSMAP 76) once, powered up while moving ~18 knots in Narragansett Bay. It came up with a position about 150 miles ENE and speed of 24 knots, with no complaints. Recycled the power and it came up correct.

Seems like the Offshore industry are the only people who know to never rely on GPS
There are questions in some exams,
whats the most accurate pos ref
whats the most unreliable
both have same answer

Be interested to see a link to a source as to how that works.

Thats very simple kalman filtering
You just need to program maximum acceleration and if a sensor exceeds that you drop it.
INS cant jump so you trust it

Modern avionics don’t use Kalman filters?

You need 3 or more sensors to compare and that only really works when one of them is a different technology and that goes wrong when 2 are gps

Did aircraft get back fitted with gps to be used in navigation??
Aircraft just didnt have gps like boats did as plenty of cockups in aircraft pretty much show that

maybe they do
and the flaw is… ( 2 dgps)
To calculate the errors in the IRSs, it works on a highly democratic system. That is, if one IRS deviates more than the other two, that IR position is considered incorrect.

Sounds like the airline industry needs some training from the offshore DP world
I know they are landing in some airports with a ground based dgps in lieu of ils and that works much better than the old ils. I guess thats only on very new aircraft?

GPS has been in some airplanes for ages, but not always how you think. Large jets were late to the game, a handheld works poorly or not at all behind the glass windshield with the embedded heating wires. For a time the better light airplanes had a LOT better avionics than the average airliner.
GPS is pretty common now on all airplanes, but you won’t see something that says GPS in the panel on most jets as a stand-alone device like you might in a Piper. The GPS sensors that feed the flight management system (FMS) are literal black boxes someplace out of sight. You can’t go swapping out displays in a 737 like you can in a C-150, the whole thing is certified together. It was awhile before certified GPS installs were a thing in a large jets compared to light aircraft.
The driver was ADS-B, no GPS, no ADS-B :wink:

  • oddly enough jet navigation can be a lot less demanding than low and slow. At 35,000 feet over land you are always in range of several VOR/DMEs, the FMS can derive position from that. Meanwhile at 3500 feet no such luck. Over oceanic airspace they just planned for drifty INS units and you didn’t fly very close to other aircraft.

Seems like the FMS failed on an error-handling problem.

The FMS (flight management system) was evidently not designed to cope with such a large and sudden discrepancy between the INS (Inertial Navigation System) and the GPS and the FMS unexpectedly failed. The pilots noticed when the autopilot starting weaving. They evidently had no reliable navigation data from the FMS and no GPS time.

That’s how I understand the article anyway.

The most serious navigation issue mentioned was the risk of entering Iran air space without clearance.

I still would like to know if the gps was spoofed from a satellite or the ground and which receiver on the aircraft got the spoofed data