BE35 PLT LEAVES ASSIGNED ALT WITHOUT ATC CLRNC BELIEVING THAT IT WAS NECESSARY TO COMPLY WITH PUBLISHED STAR ALT.

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I HAD FILED IFR FOR A FLT TO VAN NUYS; CA (VNY). WX WAS CAVU OVER THE ENTIRE RTE. THE FLT PLAN RTE FILED DID NOT INCLUDE A STAR; BUT I DID NOT INCLUDE 'NO STAR' IN THE REMARKS. ABOUT 30 MI N OF EHF WE WERE GIVEN A REVISED RTE; DIRECT LHS AND THE LYNXX 7 ARR; AND MAINTAIN 9000 FT. I STUDIED THE PUBLISHED LYNXX 7; AND NOTED THAT IT CALLED FOR DEPARTING LHS ON THE 150 DEG RADIAL. AS LHS IS ONLY 27 NM FROM VAN NUYS; I KNEW THAT A STEEP DSCNT WOULD BE NECESSARY. THE STAR SHOWS STEPDOWN ALTS FROM LHS; 7800 FT FOR THE FIRST 5 MI FROM LHS; THEN 7000 FT. I HAVE MUCH EXPERIENCE FLYING IFR; BUT I HAD NOT HAD OCCASION TO USE A STAR FOR SEVERAL YRS; THERE ARE FEW IN THE AREA I NORMALLY FLY IFR NOW. I MISTAKENLY THOUGHT THAT THE ALTS SHOWN ON THE STAR RTE WERE MANDATORY. UPON XING LHS VORTAC I TURNED TO 150 DEGS AND CALLED CTR TO ADVISE I WAS DEPARTING 9000 FT FOR THE PUBLISHED 7800 FT. I LOWERED THE GEAR AS A SPD BRAKE AND STARTED THE DSCNT. THE CTLR DID NOT RESPOND TO THE FIRST XMISSION; SO I CALLED AGAIN. HE REPLIED; 'ACFT ENDING IN X; SAY AGAIN.' I REPEATED MY XMISSION AGAIN. THE CTLR RESPONDED; 'NEGATIVE.' DON'T LEAVE THE ASSIGNED ALT UNTIL THE CTLR TELLS YOU TO. THOSE ALTS ARE FOR PLANNING PURPOSES ONLY. I NEED YOU BACK UP TO 9000 FT WITHIN 20 SECONDS OR I'LL HAVE TO SPIN YOU AROUND.' I RETURNED TO 9000 FT AND NOTHING FURTHER WAS SAID. I WAS HANDED OFF TO SOCAL APCH AND COMPLETED THE ILS APCH TO VNY WITHOUT INCIDENT. UPON RETURNING HOME I CONSULTED AIM AND NOTED THE SECTION THAT SAYS THAT ON A STAR THE LAST ASSIGNED ALT SHOULD BE MAINTAINED; AND THAT THE PUBLISHED ALTS ARE ONLY FOR PLANNING.