C560XL FLT CREW; ON DELAYED VECTOR BY ZDC; ARE ASSIGNED SQUAWK 7700 PASSING OVER R-4006; THEN RETURNED TO ORIGINAL XPONDER WHEN CLR OF RESTR AREA.

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LEVEL AT FL290 PROCEEDING FROM FAK TO OTT ON JALKE 1 ARR TO TEB. ATC ASSIGNED A SPD OF 250 KIAS; THEN SHORTLY THEREAFTER TURNED US R TO A HDG OF 100 DEGS. THERE WAS A SUBSTANTIAL AMOUNT OF TFC AND CONGESTION ON FREQ. AFTER A FEW MINS ON ASSIGNED (100 DEG) HDG; ATC CALLED US AND ASKED 'COMPANY XX; ARE YOU IN THE TURN?' WE ADVISED WE WERE ON ASSIGNED HDG. ATC THEN SAID; 'TURN L IMMEDIATELY TO 330 DEG HDG; DIRECT OTT WHEN ABLE.' WE SELECTED DIRECT TO OTT ON THE FMS'S. THEN ATC SAID 'COMPANY XX; SQUAWK EMER.' THERE WAS A PAUSE AND I BELIEVE A REQUEST TO CONFIRM. ATC CONFIRMED SQUAWK 7700 EMER. 7700 WAS SELECTED. A FEW MINS LATER ATC ADVISED 'RETURN TO PREVIOUS SQUAWK;' WHICH WE DID. SUBSEQUENTLY WE HELD AT OTT; WITH SEVERAL OTHER ACFT ENRTE TO TEB. ATC DID SAY THE EMER SQUAWK ASSIGNMENT WAS BECAUSE WE WERE 'GOING INTO PATUXENT RIVER RESTR AREA.' COMPANY COMMERCIAL ENRTE CHARTS INDICATE THAT WE WERE ABOVE ALL RESTR AREAS IN THE AREA (FL250 BEING THE HIGHEST TOP OF ANY RESTR AREA). WAS 7700 SQUAWK NECESSARY?