actually it messes up more than just the navigation. computers, cell phones, cd players set off high frequency waves that disrupt the electrical dynamics of the entire plane. this particularly applies for older planes that don't have safegards against this release of high frequency waves. so it's not just losing navigation but the whole computer system can go to wack from what i heard. think about missing your landing because some nimrod switched on his cell phone and disrupted the onboard circuitry. hypothetically you could run out of gas, crash and die. there are also several other fairly unpleasant scenarios.