ACR MLG ALT DEVIATION EXCURSION FROM CLRNC ALT IN RESPONSE TO WRONG CALL SIGN.

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COMPANY AFCE WAS A REGULARLY SCHEDULED FLT FROM LAX TO SMF; 6/88. CRUISING ON AUTOPLT AT FL310 IN THE VICINITY OF CZQ; WE WERE GIVEN A CLRNC TO DSND TO FL240 AND NOT TO EXCEED 300 KTS. I SELECTED FL240 ON THE MODE CONTROL PANEL (ALT ALERT); ADJUSTED THE SPD TO 300 KTS; AND INITIATED A DSCNT AFTER THE F/O READ BACK THE CLRNC AND IDENTED US AS COMPANY AFCE. VERY SHORTLY THEREAFTER; OAK CENTER CALLED SAYING; 'COMPANY AFCR; YOU'RE DSNDING.' WE RESPONDED VERIFYING THE DSCNT CLRNC. THE CTLR THEN TOLD US THE CLRNC WAS MEANT FOR SOMEONE ELSE. COMPANY AFEI WAS ALSO ON THE FREQ AND ALSO GOING TO SMF. ALREADY IN THE DSCNT; THE CTLR THEN TOLD US TO DSND TO FL290; WHICH WE DID. HUMAN PERFORMANCE FACTORS: THE CAPT AND F/O WERE BOTH NEW GUYS ON THE SMF RUN; AND WERE CONSEQUENTLY BEING EXTRA VIGILANT RE ROUTING; CLRNCS AND SO FORTH RELEVANT TO AN UNFAMILIAR ARPT. PERHAPS WE WERE SPRING LOADED TO TAKING THE CLRNC AND WE BOTH HEARD IT INCORRECTLY (IE; SIMILAR CALL SIGNS AND SAME DEST). WITH DEFENSE MECHANISMS FULLY ACTIVATED; HOWEVER; I'D LIKE TO THINK NOT! ANOTHER FACTOR TO BE CONSIDERED IS THAT IT WAS EARLY IN THE MORNING PACIFIC TIME. PERHAPS THE CTLR WAS A BIT FATIGUED AND MEANT TO GIVE THE CLRNC TO AFEI; BUT SAID AFCE ON THE INITIAL CALL BE MISTAKE. AGAIN; SIMILAR CALL SIGNS AND SAME DEST. IT SHOULD BE NOTED THAT CLR AND CORRECT PHRASEOLOGY WAS USED BY BOTH PARTIES IN ALL XMISSIONS; AND THE PROB APPEARS TO BE THE ISSUANCE (OR ACCEPTANCE) OF AN INCORRECT CLRNC. AS A MATTER OF CONSCIENCE; I WONDER IF IT WOULD BE POSSIBLE TO FIND OUT THROUGH A REPLAY OF THE TAPE IF: A) IT WAS AIR CREW OR CTLR ERROR; AND B) IF IT WAS AIR CREW ERROR; WHY DID WE NOT GET A CHALLENGING XMISSION TO CORRECT OUR READBACK OF 'DSND TO FL240; DO NOT EXCEED 300 KTS; AFCE.' EPILOG: IF THERE IS ANY WAY GRIEF CAN COME DOWN ON THE CTLR RE THIS INCIDENT; EITHER FOR ISSUING AN INCORRECT CLRNC OR FAILING TO CATCH OUR READBACK OF AFEI CLRNC (WHICHEVER THE CASE MAY BE); I WOULD RATHER THIS MATTER NOT BE PURSUED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: THE ARTCC RADAR CTLR SAW THE ACFT START TO DSND AND GAVE A REVISED CLRNC WHEN THE ACFT WAS ONLY 400' BELOW CRUISE ALT. REPORTER WAS ASSURED THAT WE WOULD NOT PURSUE THIS INCIDENT WITH ARTCC. THE REPORTER ALSO SAID HE CONTACTED THE SUPVR ON THE GND AND WAS TOLD THE INCIDENT WOULD NOT BE DOCUMENTED BY THE CTLR FOR ACTION.