GPS chips are receivers only, they wouldn't interfere with the aircraft's avionics. I don't know how well they would work inside of an airliner, but experiments with cell phones seem to indicate that reception is very good.

Cell phones are tracked by GPS because the GPS chip inside the cell phone relays its its position to the cell network through the cell's signal. A hundred miles off of the coast I doubt there's cell network coverage.
Hope for the best and prepare for the worst.

The object in life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane