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Related to What effect would an air-to-air GPS jamming system have?, I'm wondering whether it is possible for a terrorist (or likewise, law enforcement) to manipulate GPS signals received by a jet, re-routing it elsewhere?

I gather this would be far from a simple task, but how feasible is it?

Let's assume that this is in uncontrolled airspace, so can't spot the change in flight path.

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    $\begingroup$ it's possible but the pilot would need to ignore every other navigation aid he has available $\endgroup$ – ratchet freak Jul 22 '14 at 0:04
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Spoofing GPS means broadcasting a false GPS signal - This is harder than jamming GPS which can be done relatively easily by broadcasting a strong random signal at the relevent carrier frequencies.

GPS receivers use GPS ephemeris tables which tell them where exactly they should expect each satellite to be. So the false GPS signal has to look enough like a real GPS signal that the receiver will accept it and use it's transmitted data in it's calculations.

Of course, if, for example, the expansionist president of a country with advanced avionics capability decided to supply sophisticated equipment and the associated personnel to a separatist group in a neighbouring country, it might be possible for them to bring about this kind of result.

There have been reports of this kind of spoofing actually happening, so it appears to be possible.

The U of Texas students built a GPS spoofing device for about $3,000. A pair of students, the “attackers,” then sat aboard the upper deck of the White Rose, where their GPS spoofer emitted a counterfeit signal slightly stronger than the real GPS signal.

This was a yacht at sea, presumably out of sight of land on a featureless ocean.

It may be more difficult to achieve this with an airliner, which have a variety of navigational instruments, including radio navigation beacon receivers. Inconsistent indications may alert the pilot to a problem.

Non-GPS navigational instruments/systems that may be found in an aircraft include:

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  • $\begingroup$ The loss of an RQ-170 in December 2011 involved GPS spoofing; see this Wikipedia link, although none of this has been confirmed. GPS jamming is so dead simple that all aviation navigation requires alternatives which do not rely on GPS. However, GPS is so convenient that in many cases it is used as the primary means of navigation. $\endgroup$ – Peter Kämpf Jul 22 '14 at 20:49
  • $\begingroup$ It would be interested to know to what extent the modern navigation systems cross-reference GPS with INS. INS is always there because GPS alone has too slow response for some uses like autopilot and being completely internal INS obviously can't be spoofed, so when the systems divert more than is believable error rate of INS, the system can declare error. What I don't know is what the threshold for declaring the system failed is in practice. $\endgroup$ – Jan Hudec Mar 4 '15 at 21:03
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Yes, you could certainly do this, especially for a smaller plane like a charter that was flying an unknown route. By this means you could temporarily divert the aircraft. Note several things:

  • You would have to do it gradually; if you made a sudden change in position, the pilots would probably notice, so it would only work on a long flight

  • It would not work if the pilots knew the route well. What would happen is that the trick would start to influence the heading and the pilot would see the unexpected heading and get confused (why are we on 040? shouldn't we be on 052 to Chicago?)

  • The diverted heading would have to be roughly similar to the expected heading. For example, if the pilots know they are going north, and the diverted heading is south, they will immediately know something is wrong.

  • If it was a domestic commercial flight or at least had a flight plan with flight following activated, it would probably get noticed by ATC. For example, even a private pilot, if he has requested flight following will get notified by ATC if he starts to deviate significantly from the planned route. For this reason, a diversion would be most effective if it was an international flight or going through uncontrolled air space.

As far as the spoofing itself, it is easy as long as the person has enough expertise. Even a weak earth-bound transmitter will easily overpower real GPS signals. To create the spoofed signals the engineer can use a GPS simulator on the planned diverted route and record them. Then, they just play back the simulation record and transmit it. Note that this will only work if you know ahead of time the aircraft's planned route and speed. If you do not know ahead of time its original trajectory, you would have to observe its current flight path (by ACARS, radar or some other method), compute the diversion, simulate it and transmit it dynamically, which would be more complicated.

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    $\begingroup$ cool idea to play back pre-recorded GPS signals. Unfortunately the clock time is a very important parameter in GPS, and the systems (and pilots) would probably notice that changing. $\endgroup$ – Peter Mar 4 '15 at 18:05
  • $\begingroup$ @Peter I assume the spoofer knows the original flight plan so can make the GPS time relatively similar to the real time. $\endgroup$ – Tyler Durden Mar 4 '15 at 18:07

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