From the articles/videos I've seen, it seems that the first aircraft (AA, I guess) executed a go-around once they couldn't get a hold of twr and contacted potomac app to inquire what the problem was. After app couldn't reach the tower, the app controller (this is what i read, so don't shoot the messenger) declared the field uncontrolled and clear the aircraft for the approach. I can only assume (my opinion) that the crew then made radio calls on the tower freq and landed. The second (UA flight) did the same. Lets not get on the crews right away fro the decisions that were made quite yet. I'm sure more details will be released in the coming days.

Here's a video from CBS News