. . need a suicidal passenger on the aircraft carrying a radio transmitter powerful enough to override the ground transmitters.
I think a well placed, high power ground transmitter could easily overcome a more distant "legitimate" transmitters.
Even though this discussion has been focused on the ground/air links, I would be willing to wager that the back-end ground link portions of these systems are almost as vulnerable. Why spend money on a transmitter when you don't have to.
. . well funded, well connected entities . .
Never underestimate the power of money or determination.
