B737 FLC VIOLATE P56 AND CLAIM CONFUSING DEP PROC OFF RWY 36; ASSUMED RADAR VECTORS BUT DID NOT QUESTION THE CLRNC.

Narrative

ATC CLRNC FOR OUR DEP FROM DCA ON RWY 36 READ AS FOLLOWS: DEPART NW 328 DEGS J-149; AF; CLB TO 5000 FT; EXPECT FL310. CONFUSION; BECAUSE OF THE VAGUENESS OF THE CLRNC; OVER WHETHER TO FLY THE DCA 328 DEGS 'IMMEDIATELY' AFTER DEP OR TO EXPECT VECTORS; RESULTED. EVEN AFTER REVIEWING THE 'SPECIAL APCH/DEP PROCS' DEPICTED ON OUR (10-7) PLATE; WE WERE ASSUMING RADAR VECTORS TO OUR DEP COURSE DUE TO THE INCLEMENT WX THAT EXISTED OVER THE FIELD AND OUR INABILITY TO MAINTAIN A VISUAL WITH THE POTOMAC RIVER. OUR SPECIAL DEP PROC STATES THAT WE SHOULD AVOID PROHIBITED AREAS; P-56; BY MAKING AN IMMEDIATE L TURN AND REMAIN OVER THE POTOMAC RIVER. IT ALSO STATES NOT TO CROSS THE EAST BANK OF THE RIVER. AFTER READING THIS AND KNOWING THAT WE HAD A 400 FT CEILING IT WAS INTERPRETED THAT VECTORS WOULD BE PROVIDED TO OUR DEP RTE. CLBING OUT OF 1000 FT WE CONTACTED DEP CTL AND WERE ASKED WHAT OUR HEADING WAS. WE REPLIED 360 DEGS. OUR NEXT INSTRUCTION FROM ATC WAS TO CLB TO 11000 FT AND EXPEDITE THROUGH 9000 FT. SHORTLY AFTER THAT WE WERE GIVEN A HDG OF ABOUT 320 DEGS AND INSTRUCTED TO COPY DOWN A DCA TWR NUMBER TO CALL. I THINK THAT A MAIN CONTRIBUTING FACTOR TO OUR CONFUSION OVER THE DEP WAS THE LACK OF A PUBLISHED DEP SID IN OUR ATC CLRNC. ALSO; THERE EXISTED NO WORDS IN OUR ATC CLRNC TO ALERT US TO THE URGENCY OF AN 'IMMEDIATE' L TURN TO JOIN THE DCA 328 DEG RADIAL. IN ADDITION; THE FO; WHILE RECEIVING THE DEP CLRNC; HAD DIFFICULTY UNDERSTANDING THE CTLR AND REQUESTED MULTIPLE READBACKS. ANOTHER CONTRIBUTING FACTOR WAS THAT IT WAS MY FIRST VISIT TO DCA. AFTER REVIEWING ALL OF THE INFO THAT I HAD AVAILABLE TO ME; IT IS STILL EASY TO SEE HOW AN INCIDENT LIKE THIS COULD HAPPEN. IN FACT; I WAS INFORMED IN MY PHONE CALL TO THE DCA TWR SUPVR THAT FOUR SUCH INCIDENTS IN THE PAST 2 DAYS AND 37 OVER THE COURSE OF THE LAST YEAR HAD OCCURRED. THIS LEADS ME TO BELIEVE THAT SOME TYPE OF SYSTEMATIC PROB EXISTS; AND NEEDS TO BE FIXED. SUPPLEMENTAL INFO FROM ACN 384198: ON OCT/MON/97; OUR FLT ENCOUNTERED A POSSIBLE VIOLATION OF AIRSPACE P-56 IN THE CLOSE PROX OF THE WASHINGTON; DCA ARPT AREA.