A320 CREW WAS DIRECTED TO DIVERT TO IAD FROM DCA FOR NO APPARENT REASON.

Narrative

I WAS THE PF AND WE HAD 2 FEDERAL AIR MARSHALS ON BOARD. TKOF; CLB; CRUISE AND INITIAL DSCNT WERE ALL NORMAL. FO AND I BEGAN DISCUSSING THE RIVER VISUAL APCH INTO DCA. WE WERE CHKING TO SEE IF THE APCH WAS IN THE DATABASE OF THE COMPUTER WHEN WE RECEIVED A FREQ CHANGE. I DID HEAR THE NEW FREQ OF 119.85 BUT NOT THE CTLING AGENCY. FO AND I DISCUSSED THIS FACT AND HE CHKED THE FREQ AND FOUND IT DID NOT APPEAR AS A WASHINGTON APCH FREQ. HE THEN CHKED IN ON THE NEW FREQ. THIS IS HOW I RECALLED IT HAPPENED. ACFT X DULLES APCH ACFT X DSNDING TO 8000 FT. NOTHING HEARD FOR 5 SECONDS. WASHINGTON APCH; 'ACFT X; TURN L HDG 010 DEGS.' ACFT X; 'OH...WASHINGTON APCH; ACFT X DSNDING TO 8000 FT; INFO CODEWORD. WE WERE THEN INSTRUCTED TO LND IAD. THE APCH AND LNDG WERE UNEVENTFUL. WE WERE INSTRUCTED TO PROCEED TO RWY 30 RUNUP PAD AND MET WITH IAD OPS. I CONFIRMED ALONG WITH THE AIR MARSHALS THAT SECURITY WAS NORMAL AND WE WERE RELEASED. WE RECEIVED A NEW FLT PLAN TO DCA. AFTER LEVELING OFF; DULLES DEP TOLD US TO CONTACT WASHINGTON ON FREQ XXXXX. WE MADE 3 CALLS TO DEP BEFORE THEY CONFIRMED IT WAS WASHINGTON APCH. WE LANDED UNEVENTFULLY.