I have no idea where such an airport could've been, you'd think there would be at least some hangars or buildings somewhere. But nothing.
It wasn't until I played New Vegas that I realized how little sense Fallout 3's world makes if you actually start thinking about it. Abandoned buildings with 200 year old food supplies that never seem to have been looted, one major town whose agriculture consists of one brahmin...
Yeah I know, Fallout 3 has an amazing world, but if you think about some of its placements, you can't help but go 'Hey, wait a minute.'
Well in New Vegas bery little bombs hit, but the the Capital Wastland was directly hit with bombs thats why, new vegas seems less decay. I believe the airport they took it from was Adams Air Force Base before the Enclave got their hands on it
Adams Air Force Base anyone?
That wouldnt make sense. The elderly lady in town says Megaton started just after the bomb, and that people had been living in the impact crater to escape the dust storms. The two things wrong with your theory is that A. They said that 'The Wasteland had claimed the place', and Adams is perfectly intact. and B. Adams is to far away to logically drag entire airplanes miles and miles back to D.C., across the river, and build the town. Also, C. The aircraft look civilian, not military. At least from what I can tell.
I think the truth is Bethesda just got lazy and didnt add in the airport.