Reagan Airport is in Arlington, Virginia. Dulles is in Chantilly, Virginia, so you MIGHT be OK there. I would still be pretty wary taking a gun there. BWI is in Baltimore, so no go there. There isn't a major airport in D.C. proper. The problem is that Reagan and Dulles are administered by the Washington Metropolitan Airport Authority, which is a federal group. Both airports are federal property and are basically run by DC's finest, but there have been a few cases that clearly indicate that both airports are governed by the laws of Virginia, but that hasn't stopped them from arresting gun owners there for violating DC gun laws.