Love the idea and hope that you will share the results in the DPF here on MR. Airports can be great for documentary style photography. I have an image (sorry no JPEG) that is part of the Northern Community College permanent collection that I did at National Airport here in DC. And there is another image that I did for a photo class that I don't have a JPEG ready for. These two I hope that I might find a print that I can scan.
Otherwise here are some images that I did find that are web ready. Of the three, only the first one I am happy with. The other two mentioned above as MIA are the ones of course I m the most happy with (they were shot on film).
My concern is the post 9-11 world. A few snaps on my recent travels over the past year have not drawn attention. But I do think that after 48 hours at an airport would draw attention of security. And seeking permission may require so much paperwork, not to be worth it.

You should have seen the song and dance they wanted me to go through at Dulles for a night time photo project for college. I gave up.
Also 48 hours at an airport sounds great. But I have now flown through East and West Coast (US) airports, as well as a couple of international airports - at various times of the day. I am not sure that that there would be enough to give credence to your project. Unless you were given access to more secure areas. Or given a "pass" by being in a public area for an extended time.
For I see a photo project like this (I will not comment on video, since I have little interest in video) of ending up with 48 stunning images. The airports that I have been through in the public areas would be hard pressed for more than 18 hours of true human interest. And I have been through IAD, LGA, ORD, SFO, ATL, BOS, LHR, KEF, EWR, DCA; and so many others.