Back in the mid 1980s I had the opportunity to fly my NORDO 1941 T-Craft into Newark International. I was seriously bummed that I couldn't do it, I had some other prior commitment. How cool would that have been? I forget the details, some kind of antique airplane exhibition, they were making special arrangements for a group of NORDO antiques to fly in and out during narrow time windows.
I've witnessed a real intercept in the FRZ, and have served as a practice target aircraft. . .A good while back a CFI and student, from PA, I think, got lost and drove down the Potomac; not really NORDO, and no harm done; helicopter guys held up a sign with a freq and got it sorted. Then again, I don't think they landed at DCA.
When I was flying out of Frederick, the F-16's would escort a P-40 violator in now and then. Watching an F-16 slow flight to stay with a Skyhawk is a thing to see. As soon as the Skyhawk touched down the state police would roll onto the runway behind it and the F-16 would roar off.