DSNDING INTO HOU; AN MD80 CREW MAY HAVE CONFUSED ADING INTXN WITH HEADING AND INCORRECTLY STARTED A TURN EARLY FOR A VECTOR.

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APCH CTLR SAID 'COME R TO HDG 220 DEGS;' WHICH I READ BACK. AFTER PROCEEDING ON 220 DEGS FOR 4-5 MINS; THE CTLR CAME BACK AND SAID 'RETURN TO HDG 090 DEGS TO INTERCEPT THE STRUK 1; AND TURN TO 220 DEGS AT ADING INTXN.' THE MARIT INTXN ON THE STRUK 1 WAS MISSING FROM DATABASE AND I WAS DISTR PUTTING THAT IN THE GFMS; BUT I READ BACK THE CLRNC AND WAS NOT CHALLENGED; SO WE TOOK THE HDG VECTOR PRIOR TO ADDING THE WORD HEADING AND ADING WERE SIMILAR AND THIS MAY HAVE BEEN THE PROBABLE CAUSE. A RPT FOR THE MISSING DATABASE INTXN AT MARIT WILL BE SUBMITTED; AS THIS IS AN ALT AND A SPD RESTR POINT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR BELIEVES THE SECOND INSTRUCTION ISSUED BY THE CTLR TO TURN TO A 220 DEG HDG MAY HAVE BEEN PERFORMED PREMATURELY. HE SAID THE CTLR'S XMISSION SOUNDED AS IF IT HAD BEEN CLIPPED BUT WAS REPEATED AS HEARD AND NOT CORRECTED BY CTLR. HE NOTED THE INSTRUCTION WAS NEAR 'ADING' INTXN; WHICH IS PHONETICALLY SIMILAR TO 'HEADING.' THE RPTR SUGGESTS ADING INTXN BE CHANGED TO AVOID CONFUSION.