Apparently there was a bomb threat in one or two Dulles parking garages tonight, but it is affecting arriving flights.
NBC-Washington says on Twitter that flights were evacuated too: "#Breaking Passenger at #Dulles tells News4 that pilot told everyone on plane there's a TSA emergency - must immediately evacuate."
In reverse order from MWAA on Twitter, which is the airport opeator.
If you are flying #IAD Dulles tonight, check flight status with your airline. Airport is open and operating, but several flts delayed.
#IAD Dulles Arriving flights proceeding to gate areas; some had been temporarily held. Terminals and runways are open.
The economy and hourly lots are OPEN at #IAD Dulles if you are driving/parking here. And the terminals are open.
Terminals open at #IAD Dulles, parking garages temp closed for a police investigation. Several arriving flights delayed; will update.
And most recent update at 9:48pm " #IAD Dulles terminals, runways, flights operating normally. Daily garages remain clsd for police investigation. Hourly & Econ lots open. "
[Edited 2012-09-24 18:48:26]