AN ACR WDB FAILED TO MAKE ITS XING RESTRICTION.

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DEPARTED HONG KONG ON ASSIGNED SID; ELATO 1 ALPHA; FLT PLAN RTE. APPROX 10 MI FROM ARPT RECEIVED RADAR VECTORS AND A CLRNC TO FILED CRUISE ALT. AT APPROX 27000 FT; WE WERE THEN CLRED DIRECT ELATO INTXN WHICH WAS THE FIR BOUNDARY. SINCE THERE WAS NO VERBAL XING RESTRICTIONS GIVEN TO US; AND THE FACT THAT WE WERE ON RADAR VECTORS; LED US TO BELIEVE THAT THERE WAS NO REQUIREMENT TO BE AT FL330 (CRUISE ALT) BY THE FIR. OUR ALT XING ELATO (FIR) WAS FL310 DUE TO THE ACFT BEING HVY AND OUTSIDE AIR TEMP BEING VERY WARM. WE WERE CLBING THE BEST WE COULD UNDER THE CIRCUMSTANCES. ATC INQUIRED AS TO WHAT OUR ALT WAS XING ELATO AND THAT WE WERE SUPPOSED TO CONTACT THEM IF UNABLE TO REACH CRUISE ALT BY ELATO INTXN. ON CLOSER INSPECTION; THE CAPT AND I DISCOVERED FROM THE SID THIS TO BE THE CASE; EVEN THOUGH WE WERE BEING RADAR VECTORED WHICH WOULD NORMALLY NEGATE PREVIOUS CLRNCS; IN THIS CASE; THE SID. ALSO; AS PREVIOUSLY MENTIONED; WITH NO XING RESTRICTIONS MENTIONED AND BEING RADAR VECTORED; WE FELT THAT THIS REQUIREMENT WAS NOT IN EFFECT. I BELIEVE THAT THIS REQUIREMENT; IF IT IS IMPORTANT; SHOULD BE PRESENTED IN A MORE VISIBLE AND NOTICEABLE FASHION AS IN OTHER SIDS; FOR EXAMPLE IN THE PLAN VIEW DIAGRAM; ADJACENT TO THE FIR.