AN A300 CREW DEPARTING LAS EXPECTING THE HOOVR2 PGS RECEIVED A PDC REVISION OF COWBY2 INW; BOTH CONTAINING COWBY INTXN. THE CREW FLEW THE INCORRECT DEP.

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OUR FLT PLAN SHOWED THE LAS HOOVR2 PGS. PER COMPANY PROC; I LOADED THE RWY AND FILED SID IN THE FMS. UPON RECEIPT OF THE PDC; IT HAD A RTE CHANGE NOTED WITH LAS COWBY2 INW. I DID NOT CATCH THE '2' ON THE END OF COWBY. WHICH AFTER THE INCIDENT WAS CLR THAT IT CHANGED OUR DEP. ONE PROB THAT I SEE WAS THE NAME COWBY AND THE FIX INW WERE BOTH ON OUR RTE AND IT APPEARED THAT ATC WAS JUST MODIFYING OUR DEP VERSUS CHANGING IT COMPLETELY. ON DEP; ATC CLRED US TO FL190 WITH THE COMMENT 'COMPLY WITH RESTRS.' THE RESTR WE NOTED WAS TO CROSS COWBY AT/ABOVE 10000 FT; ON THE HOOVR2 WHICH WE THOUGHT WAS OUR CLRNC. IN RETROSPECT THEY HAD US ON THE COWBY 2 DEP WITH A 7000 FT HOLD DOWN. I HAVE NEVER MADE AN ERROR LIKE THIS AND I BELIEVE IN THIS 'SILENT PAPER COM METHOD' THAT SOMETHING AS SIGNIFICANT AS HAVING A DEP CHANGED SHOULD HAVE A HIGHLIGHTED NOTE; IE; 'DEP CHANGED.' WHILE THE RTE CHANGE WAS SOMEWHAT MISLEADING WITH THE FIX NAME; IE; COWBY ON BOTH DEP PLATES PLUS BEING THE NAME FOR ANOTHER DEP WAS MISLEADING. THE PROB AROSE FROM A NEW COMPANY PROC TO LOAD AND CHK THE EXPECTED FILED RTE. FOLLOWED BY REVIEW AND ADJUSTMENT AFTER THE PDC ARRIVES. CONTRIBUTING FACTORS: 1) COMMON NAMES OF FIXES AND DEP NAMES. 2) A FAILURE IN THE SILENT PAPER CLRNC METHOD TO HIGHLIGHT SIGNIFICANT CHANGES. 3) A FAILURE OF ATC TO CONFIRM A CHANGE IN A SILENT CLRNC. 4) NO VERBAL CONFIRMATION BY ATC; TO CONFIRM; PRIOR TO DEP OF A DEP CHANGE. 5) FORMAT OF PDC WITH RTE VERSUS DEP CHANGES. 6) DISTRS AND INTERRUPTIONS BY GND CREW/LOADERS. THE INCIDENT WAS ONLY DISCOVERED AFTER AIRBORNE WHEN ASKED BY ATC WHAT ALT WE WERE AT. CORRECTIVE ACTION: 1) A POSITIVE STATEMENT ON THE PDC THAT INDICATES A CHANGE IN ASSIGNED DEP. 2) A VERBAL CONFIRMATION WITH ATC AS TO THE DEP PROC TO BE USED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HIS ACR FILED A NON RNAV FLT PLAN BUT ATC RE-FILED HIS FLT AS RNAV AND ISSUED AN RNAV PDC WITH THE SAME NAVAIDS IN THE FLT PLAN. THAT RE-FILING ACTION LED THIS CREW TO MISTAKENLY NOT COMPLETELY RECHK THE FMC ENTERED CLRNC AND THEY COMPLETELY MISSED THE PROC. THE RPTR STATED THAT ATC DOES NOT ASK FOR THE FIRST DEP FIX PRIOR TO TKOF AS OTHER ARPTS DO WITH FMS PROCS. RPTR BELIEVES THAT SIMPLE ACT WOULD HAVE ALLEVIATED THE ERROR HE MADE IN THIS EVENT.