FLT INBOUND TO DCA ON THE IRON 3 ARR WAS DSNDED TO 7000 FT AND MAY HAVE ENTERED PROHIBITED AIRSPACE. PLTS HAD DIFFICULT COMMUNICATING WITH APCH CTL FOR VECTOR INSTRUCTIONS DUE TO FREQ CONGESTION.

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FLT X MIA-DCA. AFTER DEVIATING AROUND NUMEROUS WX CELLS; WAS ESTABLISHED ON THE IRONS 3 ARR TO DCA. HDOF WAS MADE FROM ZDC TO DCA APCH CTL. DCA APCH CLRED FLT X DIRECT TO THE DCA VOR AND DSND FROM 10000 FT TO 7000 FT. THE ACFT AHEAD WAS GIVEN A 330 DEG HDG. AT APPROX 10 DME; THE FO AND I DISCUSSED WHAT APCH MAY DO WITH US AS WE APCHED SAMMO. SAMMO FIX SHOWS A FLAG (C) AS 'HDG FOR VECTORS TO FINAL APCH COURSE.' AS WE PASSED SAMMO; MY FO MADE EFFORTS TO CONTACT APCH; HOWEVER; THE CLOSER WE GOT TO THE VOR; THE BUSIER THE APCH FREQ GOT. I HAD SLOWED THE ACFT TO 210 KIAS AT APPROX 10 DME IN ANTICIPATION OF A SLAM DUNK. AS WE ENTERED THE CONE AT THE VOR; MY FO WAS ABLE TO BREAK IN AND ASKED ABOUT THE TOP OF THE RESTR AREA. THERE WAS NO RESPONSE FROM APCH. MY FO THEN ASKED FOR A HDG. THERE WAS A HESITATION; AND WE WERE TOLD TO MAINTAIN OUR HDG. MY FO EXPRESSED HIS CONCERN TO ME ABOUT OUR ENTERING THE RESTR AREA P56. I AGREED THAT WE PROBABLY HAD. THE REMAINDER OF THE APCH AND LNDG VIA ROSSYLN LDA RWY 18 WAS UNEVENTFUL. AFTER LNDG; WE WERE GIVEN A TRACON PHONE NUMBER AND ADVISED TO CALL. I CALLED AND WAS TOLD WE HAD A P56 VIOLATION. I TALKED TO THE SUPVR AND EXPLAINED THE ABOVE. I TOLD HIM THE APPROX TIME AND ASKED HIM TO REVIEW THE TAPE. HE ADVISED ME TO CALL BACK IN 20 MINS. I CALLED FROM THE HOTEL AND WAS TOLD THAT A CTLR DEV WOULD BE ISSUED. HOWEVER; SEVERAL ISSUES ARE UNRESOLVED: 1) NOWHERE IN COMMERCIAL PUBS ARE THERE RESTR ALTS FOR P56 EXCEPT ON THE HI-4 CHART. (GOODBYE HI- 4 AT THE START OF THE STAR.) 2) NOWHERE ON ACR PAGES ARE THERE RESTR ALTS DEPICTED EXCEPT FOR PAGE 10-7V -- MT VERNON P73; 1500 FT. THE ABOVE ADD-ON'S WOULD SURELY ENHANCE CREW AWARENESS. 3) THE FAA SHOULD ESTABLISH A PRINTED VECTOR HDG OFF SAMMO TO PREVENT INCURSIONS DURING HIGH CTLR WORKLOAD. 4) GUIDANCE FROM ACR; IE; AN ESCAPE PROC; AS THIS ARR LEADS OUR CREWS INTO POTENTIAL VIOLATIONS.