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 atc can't spot the change in flight path.
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:
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.
Also, don't forget that EVERY GPS receiver in the area of effect will receive the spoofed signal, so if it is broadcast in a populated area, you will have thousands of cars, phones and boats all receiving the spoofed signal.
