OK, here we go. I am a US citizen with feet, boat, car, and plane. They are all owned by ME. If I want to leave this country by plane, I need permission from the feds or I will be committing a felony. If we are going to do this right, we then must require all citizens to notify the feds when they want to walk, boat, or drive across the border.
Now, I don't care if it's any of the four common modes of transportation, if I own the conveyance and I'm operating it, then the rules should be the same. Walk, float, drive, fly - either you notify the feds in advance, and get permission, or you don't.
As for 121, etc I have already stated that I don't think the feds need to know when a citizen leave the country or not. In fact, if I ran things, I would prohibit the feds from gathering info on the movement of any US citizens at any time without a warrant issued by a fed judge. But that is just me.