I don't think precise location data is necessary to guide an airliner to Washington or New York. Even a primitive knowledge of dead-reckoning navigation would have got them close enough to pick up adequate visual references to complete the mission by pilotage. Would a consumer-grade circa 2001 GPS even be capable of acquiring a useful fix in an airliner?

But the fundamental reality is that anyone who ever tries to hijack an airliner will be killed by the passengers.