ENRTE TO LAS; B737-300 FO CHANGES FMS ARR RTE WITHOUT ADVISING CAPT AND IS CHALLENGED BY L30 ON APCH.

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BEFORE PUSH; THE FO LOADED THE CORRECT RTE IN THE FMS. THE RTE WAS CHKED AND BRIEFED. AT SOME POINT IN THE FLT; THE FO CHANGED THE ARR FROM THE GRNPA TO THE KSINO. I DID NOT NOTICE HIM MAKE THE CHANGE. DISCOVERED: AT LUXOR; THE APCH CTLR CLRED US DIRECT GRNPA. AS WE DID NOT HAVE GRNPA IN OUR RTE; WE COULD NOT UNDERSTAND WHY WE WERE BEING CLRED THERE. THE CTLR ASKED WHAT ARR WE WERE FLYING. HE THEN GAVE US A VECTOR OFF THE ARR TO INTERCEPT THE RWY 25R LOC. CONTRIBUTING FACTORS: I HAVE HAD NO TRAINING ON THE LNAV SYS. THERE ARE TOO MANY ARRS INTO LAS THAT ARE VERY CLOSE TO EACH OTHER. THEY LOOK THE SAME. AT NO TIME DID THE CTR OR APCH SAY WHAT ARR WE WERE TO FLY AFTER THEY TOOK US OFF THE FILED RTE AND GAVE US DIRECT TO A FIX (LAST FIX WAS LUXOR). IT DOES NOT HELP TO HAVE THE SAME FIXES ON DIFFERENT ARRS. LUXOR IS ON 3 ARRS AS IS KSINO. THERE ARE 18 ARRS. PREVENTION: THE SAME FIX ON DIFFERENT ARRS SHOULD NOT BE USED. IT IS ASKING FOR CONFUSION BTWN THE ARRS. FLTS SHOULD BE CLRED ONTO THE ARR TO BE USED BY THE CTLR WHO IS IN CONTACT WITH THAT FLT JUST PRIOR TO STARTING THE ARR; THE SAME AS BEING CLRED FOR AN APCH. CTLRS DON'T JUST LET US FLY AN APCH. WHY SHOULD AN ARR BE DIFFERENT? THE PROGRAMMING OF OUR FLT PLANS BY THE COMPANY IN THE FMC IS NOT VERY GOOD. WE HAVE TO MAKE A LOT OF CORRECTIONS; SO IT IS NOT UNUSUAL FOR AN FO TO HAVE TO MAKE A LOT OF CHANGES TO THE RTE. WHEN MAKING CHANGES IS COMMON; IT IS EASY TO MAKE MISTAKES OR MISS SOMETHING. THE COMPANY NEEDS TO DO A BETTER JOB IN THIS AREA. THE LNAV SYS IS A SINGLE SYS. IT IS PROGRAMMED BY 1 PERSON. IF EACH PLT HAD AN INDEPENDENT LNAV SYS AND PROGRAMMED IT; DISCREPANCIES IN THE RTE WOULD SHOW UP. WITH A SINGLE SYS; THERE IS NO BACKUP. 'GARBAGE IN; GARBAGE OUT.' SUPPLEMENTAL INFO FROM ACN 602530: WE WERE CLRED BY SLC CLRNC DELIVERY TO FLY THE GRNPA RNAV ARR INTO LAS. THIS IS THE ARR THAT WAS PROGRAMMED INTO THE FMS. WHEN AT CRUISE; I WENT TO CHK THE ARR AGAINST THE LEGS PAGE; I GRABBED THE KSINO TWO RNAV. WHERE I MADE MY MISTAKE WAS AFTER LUXOR I DELETED THE INTXNS ON THE GRNPA. ARR AND TYPED IN THE INTXNS ON THE KSINO. ARR. PRIOR TO REACHING MLF INTXN; WE WERE CLRED DIRECT KSINO THEN DIRECT LUXOR THEN DIRECT GRNPA. THE CTLR NEVER STATED AT ANY TIME THAT WE WERE CLRED VIA THE 'GRNPA. ARR TO LAS' LIKE THEY NORMALLY DO. IF HE HAD; WE MAY HAVE CAUGHT OUR MISTAKE.