Commercial Flights Are Experiencing ‘Unthinkable’ GPS Attacks and Nobody Knows What to Do::New “spoofing” attacks resulting in total navigation failure have been occurring above the Middle East for months, which is “highly significant” for airline safety.
They use gyroscopes and accelerometers to measure the aircrafts movement from the starting position at takeoff. That can then be used to plot the course the aircraft has taken to show the current location.